Articles de revues : « Forest-Atmosphere exchanges »

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Serra-Neto, Edivaldo M., Hardiney S. Martins, Cléo Q. Dias-Júnior, Raoni A. Santana, Daiane V. Brondani, Antônio O. Manzi, Alessandro C. de Araújo, Paulo R. Teixeira, Matthias Sörgel et Luca Mortarini. « Simulation of the Scalar Transport above and within the Amazon Forest Canopy ». Atmosphere 12, n^o 12 (7 décembre 2021) : 1631. http://dx.doi.org/10.3390/atmos12121631.

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The parallelized large-eddy simulation model (PALM) was used to understand better the turbulent exchanges of a passive scalar above and within a forested region located in the central Amazon. Weak (2 ms−1) and strong (6 ms−1) wind conditions were simulated. A passive scalar source was introduced to the forest floor for both simulations. The simulations reproduced the main characteristics of the turbulent flow and of the passive scalar transport between the forest and the atmosphere. Noteworthily, strong and weak wind conditions presented different turbulence structures that drove different patterns of scalar exchange both within and above the forest. These results show how passive scalar concentration is influenced by the wind speed at the canopy top. Additionally, higher wind speeds are related to stronger sweep and ejection regimes, generating more intense plumes that are able to reduce the passive scalar concentration inside the forest canopy. This work was the first that used PALM to investigate scalar transport between the Amazon rainforest and the atmosphere.

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Wiedinmyer, Christine, Michael Barlage, Mukul Tewari et Fei Chen. « Meteorological Impacts of Forest Mortality due to Insect Infestation in Colorado ». Earth Interactions 16, n^o 2 (1 février 2012) : 1–11. http://dx.doi.org/10.1175/2011ei419.1.

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Abstract Physical characteristics of forests and other ecosystems control land–atmosphere exchanges of water and energy and partly dictate local and regional meteorology. Insect infestation and resulting forest dieback can alter these characteristics and, further, modify land–atmosphere exchanges. In the past decade, insect infestation has led to large-scale forest mortality in western North America. This study uses a high-resolution mesoscale meteorological model coupled with a detailed land surface model to investigate the sensitivity of near-surface variables to insect-related forest mortality. The inclusion of this land surface disturbance in the model increased in simulated skin temperature by as much as 2.1 K. The modeled 2-m temperature increased an average of 1 K relative to the default simulations. A latent to sensible heat flux shift with a magnitude of 10%–15% of the available energy in the forested ecosystem was predicted after the inclusion of insect infestation and forest dieback. Although results were consistent across multiple model configurations, the characteristics of forests affected by insect infestations must be better constrained to more accurately predict their impacts. Despite the limited duration of the simulations (one week), these initial results suggest the importance of including large-scale forest mortality due to insect infestation in meteorological models and highlight the need for better observations of the characteristics and exchanges of these disturbed landscapes.

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Pinheiro, Di Angelo Matos, Cléo Quaresma Dias-Júnior, Leonardo Deane de Abreu Sá et Antonio Ocimar Manzi. « Usando a altura do ponto de inflexão no perfil do vento para a obtenção de perfis adimensionais acima da floresta amazônica ». Ciência e Natura 42 (28 août 2020) : e24. http://dx.doi.org/10.5902/2179460x53225.

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The most turbulent vortices that populate the forest-atmosphere interface have canopy height length scales. These vortices are mainly responsible for turbulent exchanges between inside and above canopy region. Thus, we used the vertical wind profiles obtained by 10 anemometers installed inside and above the forest canopy of the Rebio-Jarú experimental site, in the Amazon Rainforest. A third degree polynomial function was developed to better fit the wind profile and therefore estimate the inflection point height of the vertical wind profile (zi) a length scale associated with wind shear (Ls), and the wind speed at height zi. These length and velocity scales were used to obtain better fits for the dimensional wind profiles and turbulence statistical moments. Three dimensionless profile models were compared using friction velocity, wind velocity in zi and wind velocity at canopy height. It was observed that the dimensionless profiles using the velocity and shear calculated at zi provided support for the elaboration of more realistic parameterization of the turbulent exchange processes that occur both at the forest-atmosphere interface and inside the canopy.

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Smallman, T. L., J. B. Moncrieff et M. Williams. « WRFv3.2-SPAv2 : development and validation of a coupled ecosystem–atmosphere model, scaling from surface fluxes of CO2 ; and energy to atmospheric profiles ». Geoscientific Model Development 6, n^o 4 (29 juillet 2013) : 1079–93. http://dx.doi.org/10.5194/gmd-6-1079-2013.

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Abstract. The Weather Research and Forecasting meteorological (WRF) model has been coupled to the Soil–Plant–Atmosphere (SPA) terrestrial ecosystem model, to produce WRF-SPA. SPA generates realistic land–atmosphere exchanges through fully coupled hydrological, carbon and energy cycles. The addition of a~land surface model (SPA) capable of modelling biospheric CO2 exchange allows WRF-SPA to be used for investigating the feedbacks between biosphere carbon balance, meteorology, and land use and land cover change. We have extensively validated WRF-SPA using multi-annual observations of air temperature, turbulent fluxes, net radiation and net ecosystem exchange of CO2 at three sites, representing the dominant vegetation types in Scotland (forest, managed grassland and arable agriculture). For example air temperature is well simulated across all sites (forest R2 = 0.92, RMSE = 1.7 °C, bias = 0.88 °C; managed grassland R2 = 0.73, RMSE = 2.7 °C, bias = −0.30 °C; arable agriculture R2 = 0.82, RMSE = 2.2 °C, bias = 0.46 °C; RMSE, root mean square error). WRF-SPA generates more realistic seasonal behaviour at the site level compared to an unmodified version of WRF, such as improved simulation of seasonal transitions in latent heat flux in arable systems. WRF-SPA also generates realistic seasonal CO2 exchanges across all sites. WRF-SPA is also able to realistically model atmospheric profiles of CO2 over Scotland, spanning a 3 yr period (2004–2006), capturing both profile structure, indicating realistic transport, and magnitude (model–data residual

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Smallman, T. L., J. B. Moncrieff et M. Williams. « WRFv3.2-SPAv2 : development and validation of a coupled ecosystem-atmosphere model, scaling from surface fluxes of CO2 ; and energy to atmospheric profiles ». Geoscientific Model Development Discussions 6, n^o 1 (4 mars 2013) : 1559–98. http://dx.doi.org/10.5194/gmdd-6-1559-2013.

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Abstract. The Weather Research & Forecasting meteorological (WRF) model has been coupled to the Soil Plant Atmosphere (SPA) terrestrial ecosystem model, to produce WRF-SPA. SPA generates realistic land-atmosphere exchanges through fully coupled hydrological, carbon and energy cycles. The addition of a land surface model (SPA) capable of modelling biospheric CO2 exchange allows WRF-SPA to be used for investigating the feedbacks between biosphere carbon balance, meteorology and land management/land use change. We have extensively validated WRF-SPA using multi-annual observations of air temperature, turbulent fluxes, net radiation and net ecosystem exchange of CO2 at three sites, representing the dominant vegetation types in Scotland (forest, managed grassland and arable agriculture). WRF-SPA generates more realistic seasonal behaviour at the site level compared to an unmodified version of WRF, and produces realistic CO2 exchanges. WRF-SPA is also able to realistically model atmospheric profiles of CO2 over Scotland, spanning a 3 yr period (2004–2006), capturing both profile structure, indicating realistic transport, and magnitude indicating appropriate source sink distribution and CO2 exchange. WRF-SPA makes use of CO2 tracer pools and can therefore identify and quantify land surface contributions to the modelled atmospheric CO2 signal at a specified location.

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Barr, Jordan G., Vic Engel, José D. Fuentes, Joseph C. Zieman, Thomas L. O'Halloran, Thomas J. Smith et Gordon H. Anderson. « Controls on mangrove forest-atmosphere carbon dioxide exchanges in western Everglades National Park ». Journal of Geophysical Research : Biogeosciences 115, G2 (juin 2010) : n/a. http://dx.doi.org/10.1029/2009jg001186.

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Savage, K., T. R. Moore et P. M. Crill. « Methane and carbon dioxide exchanges between the atmosphere and northern boreal forest soils ». Journal of Geophysical Research : Atmospheres 102, n^o D24 (1 décembre 1997) : 29279–88. http://dx.doi.org/10.1029/97jd02233.

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Lamaux, E., A. Labatut, J. Fontan, A. Lopez, A. Druilhet et Y. Brunet. « Biosphere atmosphere exchanges : Ozone and aerosol dry deposition velocities over a pine forest ». Environmental Monitoring and Assessment 31-31, n^o 1-2 (mai 1994) : 175–81. http://dx.doi.org/10.1007/bf00547194.

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Abril, Adriana B., Patricia A. Torres et Enrique H. Bucher. « The importance of phyllosphere microbial populations in nitrogen cycling in the Chaco semi-arid woodland ». Journal of Tropical Ecology 21, n^o 1 (janvier 2005) : 103–7. http://dx.doi.org/10.1017/s0266467404001981.

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In tropical rain forest, the interface between leaf surfaces and the atmosphere is a fundamental pathway for nutrient cycling (particulary nitrogen), possibly even more important than the soil–plant interface (Parker 1994, Silver et al. 1996). Most important nutrient exchanges in the phyllosphere–atmosphere interface are mediated by microbial populations. For example, some authors have considered that nitrogen fixation in the phyllosphere is the main mechanism for nitrogen gain in humid tropical ecosystems, because of the substantial nutrient demand resulting from a high plant productivity and the constraint imposed by the generally low nitrogen availability in soil (Ruinen 1974, Salati et al. 1982, Silver et al. 1996).

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King, Gary M., et M. Hungria. « Soil-Atmosphere CO Exchanges and Microbial Biogeochemistry of CO Transformations in a Brazilian Agricultural Ecosystem ». Applied and Environmental Microbiology 68, n^o 9 (septembre 2002) : 4480–85. http://dx.doi.org/10.1128/aem.68.9.4480-4485.2002.

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ABSTRACT Although anthropogenic land use has major impacts on the exchange of soil and atmosphere gas in general, relatively little is known about its impacts on carbon monoxide. We compared soil-atmosphere CO exchanges as a function of land use, crop type, and tillage treatment on an experimental farm in Parãna, Brazil, that is representative of regionally important agricultural ecosystems. Our results showed that cultivated soils consumed CO at rates between 3 and 6 mg of CO m−2 day−1, with no statistically significant effect of tillage method or crop. However, CO exchange for a pasture soil was near zero, and an unmanaged woodlot emitted CO at a rate of 9 mg of CO m−2 day−1. Neither nitrite, aluminum sulfate, nor methyl fluoride additions affected CO consumption by tilled or untilled soils from soybean plots, indicating that CO oxidation did not depend on ammonia oxidizers and that CO oxidation patterns differed in part from patterns reported for forest soils. The apparent Km for CO uptake, 5 to 11 ppm, was similar to values reported for temperate forest soils; V max values, approximately 1 μg of CO g (dry weight)−1 h−1, were comparable for woodlot and cultivated soils in spite of the fact that the latter consumed CO under ambient conditions. Short-term (24-h) exposure to elevated levels of CO (10% CO) partially inhibited uptake at lower concentrations (i.e., 100 ppm), suggesting that the sensitivity to CO of microbial populations that are active in situ differs from that of known carboxydotrophs. Soil-free soybean and corn roots consumed CO when they were incubated with 100-ppm concentrations and produced CO when they were incubated with ambient concentrations. These results document for the first time a role for cultivated plant roots in the dynamics of CO in an agricultural ecosystem.

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Lamaud, E., Y. Brunet, A. Labatut, A. Lopez, J. Fontan et A. Druilhet. « The Landes experiment : Biosphere-atmosphere exchanges of ozone and aerosol particles above a pine forest ». Journal of Geophysical Research 99, n^o D8 (1994) : 16511. http://dx.doi.org/10.1029/94jd00668.

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Eerdekens, G., L. Ganzeveld, J. Vilà-Guerau de Arellano, T. Klüpfel, V. Sinha, N. Yassaa, J. Williams et al. « Flux estimates of isoprene, methanol and acetone from airborne PTR-MS measurements over the tropical rainforest during the GABRIEL 2005 campaign ». Atmospheric Chemistry and Physics Discussions 8, n^o 4 (8 juillet 2008) : 12903–69. http://dx.doi.org/10.5194/acpd-8-12903-2008.

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Abstract. Tropical forests are a strong source of biogenic volatile organic compounds (BVOCs) to the atmosphere and such emissions can impact the atmospheric oxidation capacity. Here we present airborne and ground-based BVOC measurements performed during the long dry season in October 2005 during the GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) project, which covered a large area of the northern Amazonian rainforest (6–3° N, 50–59° W). The vertical (35 m to 10 km) and diurnal (09:00–16:00) profiles of selected BVOCs like isoprene, its oxidation products methacrolein and methyl vinyl ketone, methanol and acetone, measured by PTRMS (Proton Transfer Reaction Mass Spectrometry), have been used to empirically estimate their emission fluxes from the forest canopy on a regional scale. The mixed layer isoprene emission flux, inferred from the airborne measurements above 300 m, is 4.1 mg isoprene m−2 h−1 whereas the surface flux is 7.3 mg isoprene m−2 h−1 after compensating for chemistry. This surface flux is in general agreement with previous tropical forest studies. Mixed layer fluxes of 0.8 mg methanol m−2 h−1 and 0.35 mg acetone m−2 h−1 were found. The BVOC measurements were compared with fluxes and mixing ratios simulated with a single-column model (SCM). The isoprene flux inferred from the measurements is substantially smaller than that simulated with an SCM implementation of MEGAN (Model of the Exchange of Gases between the Atmosphere and Nature) though consistent with global emission estimates. The exchanges of methanol and acetone can be reasonably well described using a compensation point approach.

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Pastorelli, Roberta, Isabella De Meo et Alessandra Lagomarsino. « The Necrobiome of Deadwood : The Life after Death ». Ecologies 4, n^o 1 (22 décembre 2022) : 20–38. http://dx.doi.org/10.3390/ecologies4010003.

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In recent decades, sustainable forest management has been increasingly recognized, promoting the diffusion of silvicultural practices aimed at considering all components of the forest system. Deadwood is an important component of the forest ecosystem. It plays a fundamental role in providing nutrients and habitats for a wide variety of saprotrophic and heterotrophic organisms and significantly contributes to soil formation and carbon storage. Deadwood is inhabited by a plethora of organisms from various kingdoms that have evolved the ability to utilize decaying organic matter. This community, consisting of both eukaryotic and prokaryotic species, can be defined as “necrobiome”. Through the interactions between its various members, the necrobiome influences the decay rates of deadwood and plays a crucial role in the balance between organic matter decomposition, carbon sequestration, and gas exchanges (e.g., CO2) with the atmosphere. The present work aims to provide an overview of the biodiversity and role of the microbial communities that inhabit deadwood and their possible involvement in greenhouse gas (CO2, N2O, and CH4) emissions.

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Moreaux, Virginie, Simon Martel, Alexandre Bosc, Delphine Picart, David Achat, Christophe Moisy, Raphael Aussenac et al. « Energy, water and carbon exchanges in managed forest ecosystems : description, sensitivity analysis and evaluation of the INRAE GO+ model, version 3.0 ». Geoscientific Model Development 13, n^o 12 (1 décembre 2020) : 5973–6009. http://dx.doi.org/10.5194/gmd-13-5973-2020.

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Abstract. The mechanistic model GO+ describes the functioning and growth of managed forests based upon biophysical and biogeochemical processes. The biophysical and biogeochemical processes included are modelled using standard formulations of radiative transfer, convective heat exchange, evapotranspiration, photosynthesis, respiration, plant phenology, growth and mortality, biomass nutrient content, and soil carbon dynamics. The forest ecosystem is modelled as three layers, namely the tree overstorey, understorey and soil. The vegetation layers include stems, branches and foliage and are partitioned dynamically between sunlit and shaded fractions. The soil carbon submodel is an adaption of the Roth-C model to simulate the impact of forest operations. The model runs at an hourly time step. It represents a forest stand covering typically 1 ha and can be straightforwardly upscaled across gridded data at regional, country or continental levels. GO+ accounts for both the immediate and long-term impacts of forest operations on energy, water and carbon exchanges within the soil–vegetation–atmosphere continuum. It includes exhaustive and versatile descriptions of management operations (soil preparation, regeneration, vegetation control, selective thinning, clear-cutting, coppicing, etc.), thus permitting the effects of a wide variety of forest management strategies to be estimated: from close to nature to intensive. This paper examines the sensitivity of the model to its main parameters and estimates how errors in parameter values are propagated into the predicted values of its main output variables.The sensitivity analysis demonstrates an interaction between the sensitivity of variables, with the climate and soil hydraulic properties being dominant under dry conditions but the leaf biochemical properties being most influential with wet soil. The sensitivity profile of the model changes from short to long timescales due to the cumulative effects of the fluxes of carbon, energy and water on the stand growth and canopy structure. Apart from a few specific cases, the model simulations are close to the values of the observations of atmospheric exchanges, tree growth, and soil carbon and water stock changes monitored over Douglas fir, European beech and pine forests of different ages. We also illustrate the capacity of the GO+ model to simulate the provision of key ecosystem services, such as the long-term storage of carbon in biomass and soil under various management and climate scenarios.

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Fang, H., G. Yu, S. Cheng, S. Li, Y. Wang, J. Yan, M. Wang, M. Cao et M. Zhou. « Effects of multiple environmental factors on CO2 ; emission and CH4 ; uptake from old-growth forest soils ». Biogeosciences Discussions 6, n^o 4 (31 juillet 2009) : 7821–52. http://dx.doi.org/10.5194/bgd-6-7821-2009.

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Abstract. To assess contribution of multiple environmental factors to actual carbon exchanges between the atmosphere and forest soils, four old-growth forests referred to as boreal coniferous forest, temperate needle-broadleaved mixed forest, subtropical evergreen broadleaved forest and tropical seasonal rain forest were selected along the eastern China. In each old-growth forest, soil CO2 and CH4 fluxes were measured for three years using the static chamber and gas chromatography technique. Soil temperature and moisture at the 10 cm depth were measured simultaneously with the greenhouse gas measurements. Inorganic N (NH4+-N and NO3--N) in the 0–10 cm was determined monthly. From north to south, annual mean CO2 flux ranged from 18.09±0.22 to 35.40±2.24 Mg CO2 ha−1 yr−1 and annual mean CH4 flux ranged from -0.04±0.11 to -5.15±0.96 kg CH4 ha−1 yr−1. Soil CO2 fluxes in the old-growth forests were mainly driven by soil temperature, followed by soil moisture and NO3--N. Based on the gradient theory of exchange of time and space, increase in air temperature in the future would promote soil CO2 emission in the old-growth forests. The responses of soil CH4 uptake to warming were dependent upon the critical temperature in forest. In addition, the NO3--N promotion to CO2 emission could partially attribute to the compound effects of high nitrate stimulation on soil microbe activities and increased decomposability of organic materials. The mechanism of NH4+ inhibition to CH4 uptake included both a competitive inhibition of CH4 mono-oxygenase enzyme and a toxic inhibition by hydroxylamine or nitrite produced via NH4+ oxidation. Overall, increasing in precipitation and nitrogen deposition in eastern China would increase soil CO2 emission, but decrease soil CH4 uptake in the old-growth forests.

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Arain, M. A., T. A. Black, A. G. Barr, P. G. Jarvis, J. M. Massheder, D. L. Verseghy et Z. Nesic. « Effects of seasonal and interannual climate variability on net ecosystem productivity of boreal deciduous and conifer forests ». Canadian Journal of Forest Research 32, n^o 5 (1 mai 2002) : 878–91. http://dx.doi.org/10.1139/x01-228.

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The response of net ecosystem productivity (NEP) and evaporation in a boreal aspen (Populus tremuloides Michx.) forest and a black spruce (Picea mariana (Mill.) BSP) forest in Canada was compared using a newly developed realistic model of surface-atmosphere exchanges of carbon dioxide (CO2), water vapor, and energy as well as eddy covariance flux measurements made over a 6-year period (1994-1999). The model was developed by incorporating a process-based two-leaf (sunlit and shaded) canopy conductance and photosynthesis submodel in the Canadian Land Surface Scheme (CLASS). A simple submodel of autotrophic and heterotrophic respiration was combined with the photosynthesis model to simulate NEP. The model performed well in simulating half-hourly, daily, and monthly mean CO2 exchange and evaporation values in both deciduous and coniferous forests. Modeled and measured results showed a linear relationship between CO2 uptake and evaporation, and for each kilogram of water transpired, approximately 3 g of carbon (C) were photosynthesized by both ecosystems. The model results confirmed that the aspen forest was a weak to moderate C sink with considerable interannual variability in C uptake. In the growing season, the C uptake capacity of the aspen forest was over twice that of the black spruce forest. Warm springs enhanced NEP in both forests; however, high mid-summer temperatures appear to have significantly reduced NEP at the black spruce forest as a result of increased respiration. The model suggests that the black spruce forest is a weak C sink in cool years and a weak C source in warm years. These results show that the C balance of these two forests is sensitive to seasonal and interannual climatic variability and stresses the importance of continuous long-term flux measurement to confirm modeling results.

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Ruiz-Pérez, Guiomar, Samuli Launiainen et Giulia Vico. « Role of Plant Traits in Photosynthesis and Thermal Damage Avoidance under Warmer and Drier Climates in Boreal Forests ». Forests 10, n^o 5 (8 mai 2019) : 398. http://dx.doi.org/10.3390/f10050398.

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In the future, boreal forests will face warmer and in some cases drier conditions, potentially resulting in extreme leaf temperatures and reduced photosynthesis. One potential and still partially unexplored avenue to prepare boreal forest for future climates is the identification of plant traits that may support photosynthetic rates under a changing climate. However, the interplay among plant traits, soil water depletion and the occurrence of heat stress has been seldom explored in boreal forests. Here, a mechanistic model describing energy and mass exchanges among the soil, plant and atmosphere is employed to identify which combinations of growing conditions and plant traits allow trees to simultaneously keep high photosynthetic rates and prevent thermal damage under current and future growing conditions. Our results show that the simultaneous lack of precipitation and warm temperatures is the main trigger of thermal damage and reduction of photosynthesis. Traits that facilitate the coupling of leaves to the atmosphere are key to avoid thermal damage and guarantee the maintenance of assimilation rates in the future. Nevertheless, the same set of traits may not maximize forest productivity over current growing conditions. As such, an effective trait selection needs to explicitly consider the expected changes in the growing conditions, both in terms of averages and extremes.

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Horemans, Joanna A., Alexandra Henrot, Christine Delire, Chris Kollas, Petra Lasch-Born, Christopher Reyer, Felicitas Suckow, Louis François et Reinhart Ceulemans. « Combining multiple statistical methods to evaluate the performance of process-based vegetation models across three forest stands ». Central European Forestry Journal 63, n^o 4 (26 septembre 2017) : 153–72. http://dx.doi.org/10.1515/forj-2017-0025.

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AbstractProcess-based vegetation models are crucial tools to better understand biosphere-atmosphere exchanges and ecophysiological responses to climate change. In this contribution the performance of two global dynamic vegetation models, i.e. CARAIB and ISBACC, and one stand-scale forest model, i.e. 4C, was compared to long-term observed net ecosystem carbon exchange (NEE) time series from eddy covariance monitoring stations at three old-grown European beech (Fagus sylvatica L.) forest stands. Residual analysis, wavelet analysis and singular spectrum analysis were used beside conventional scalar statistical measures to assess model performance with the aim of defining future targets for model improvement. We found that the most important errors for all three models occurred at the edges of the observed NEE distribution and the model errors were correlated with environmental variables on a daily scale. These observations point to possible projection issues under more extreme future climate conditions. Recurrent patterns in the residuals over the course of the year were linked to the approach to simulate phenology and physiological evolution during leaf development and senescence. Substantial model errors occurred on the multi-annual time scale, possibly caused by the lack of inclusion of management actions and disturbances. Other crucial processes defined were the forest structure and the vertical light partitioning through the canopy. Further, model errors were shown not to be transmitted from one time scale to another. We proved that models should be evaluated across multiple sites, preferably using multiple evaluation methods, to identify processes that request reconsideration.

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Napoly, Adrien, Aaron Boone, Patrick Samuelsson, Stefan Gollvik, Eric Martin, Roland Seferian, Dominique Carrer, Bertrand Decharme et Lionel Jarlan. « The interactions between soil–biosphere–atmosphere (ISBA) land surface model multi-energy balance (MEB) option in SURFEXv8 – Part 2 : Introduction of a litter formulation and model evaluation for local-scale forest sites ». Geoscientific Model Development 10, n^o 4 (18 avril 2017) : 1621–44. http://dx.doi.org/10.5194/gmd-10-1621-2017.

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Abstract. Land surface models (LSMs) need to balance a complicated trade-off between computational cost and complexity in order to adequately represent the exchanges of energy, water and matter with the atmosphere and the ocean. Some current generation LSMs use a simplified or composite canopy approach that generates recurrent errors in simulated soil temperature and turbulent fluxes. In response to these issues, a new version of the interactions between soil–biosphere–atmosphere (ISBA) land surface model has recently been developed that explicitly solves the transfer of energy and water from the upper canopy and the forest floor, which is characterized as a litter layer. The multi-energy balance (MEB) version of ISBA is first evaluated for three well-instrumented contrasting local-scale sites, and sensitivity tests are performed to explore the behavior of new model parameters. Second, ISBA-MEB is benchmarked against observations from 42 forested sites from the global micro-meteorological network (FLUXNET) for multiple annual cycles.It is shown that ISBA-MEB outperforms the composite version of ISBA in improving the representation of soil temperature, ground, sensible and, to a lesser extent, latent heat fluxes. Both versions of ISBA give comparable results in terms of simulated latent heat flux because of the similar formulations of the water uptake and the stomatal resistance. However, MEB produces a better agreement with the observations of sensible heat flux than the previous version of ISBA for 87.5 % of the simulated years across the 42 forested FLUXNET sites. Most of this improvement arises owing to the improved simulation of the ground conduction flux, which is greatly improved using MEB, especially owing to the forest litter parameterization. It is also shown that certain processes are also modeled more realistically (such as the partitioning of evapotranspiration into transpiration and ground evaporation), even if certain statistical performances are neutral. The analyses demonstrate that the shading effect of the vegetation, the explicit treatment of turbulent transfer for the canopy and ground, and the insulating thermal and hydrological effects of the forest floor litter turn out to be essential for simulating the exchange of energy, water and matter across a large range of forest types and climates.

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Barr, J. G., J. D. Fuentes, M. S. DeLonge, T. L. O'Halloran, D. Barr et J. C. Zieman. « Influences of tidal energy advection on the surface energy balance in a mangrove forest ». Biogeosciences Discussions 9, n^o 8 (30 août 2012) : 11739–65. http://dx.doi.org/10.5194/bgd-9-11739-2012.

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Abstract. Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL. Forest-atmosphere energy exchanges were quantified with an eddy covariance system deployed on a flux tower. The lateral energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, tidal flows reduced the impact of high radiational loads on the mangrove forest. Including tidal energy advection in the surface energy balance improved the 30-min daytime energy closure from 73% to 82% over the study period. Also, the cumulative sum of energy output improved from 79% to 91% of energy input during the study period. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem response to changing climate and regional freshwater management practices.

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Barr, J. G., J. D. Fuentes, M. S. DeLonge, T. L. O'Halloran, D. Barr et J. C. Zieman. « Summertime influences of tidal energy advection on the surface energy balance in a mangrove forest ». Biogeosciences 10, n^o 1 (25 janvier 2013) : 501–11. http://dx.doi.org/10.5194/bg-10-501-2013.

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Abstract. Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive 10-day study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL, USA. Forest–atmosphere turbulent exchanges of energy were quantified with an eddy covariance system installed on a 30-m-tall flux tower. Energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, flood waters reduced the impact of high radiational loads on the mangrove forest. Also, the regression slope of available energy versus sink terms increased from 0.730 to 0.754 and from 0.798 to 0.857, including total enthalpy change in the water column in the surface energy balance for 30-min periods and daily daytime sums, respectively. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem response to changing climate and regional freshwater management practices.

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Liu, Zelin, Changhui Peng, Louis De Grandpré, Jean-Noël Candau, Xiaolu Zhou et Daniel Kneeshaw. « Development of a New TRIPLEX-Insect Model for Simulating the Effect of Spruce Budworm on Forest Carbon Dynamics ». Forests 9, n^o 9 (24 août 2018) : 513. http://dx.doi.org/10.3390/f9090513.

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The spruce budworm (SBW) defoliates and kills conifer trees, consequently affecting carbon (C) exchanges between the land and atmosphere. Here, we developed a new TRIPLEX-Insect sub-model to quantify the impacts of insect outbreaks on forest C fluxes. We modeled annual defoliation (AD), cumulative defoliation (CD), and tree mortality. The model was validated against observed and published data at the stand level in the North Shore region of Québec and Cape Breton Island in Nova Scotia, Canada. The results suggest that TRIPLEX-Insect performs very well in capturing tree mortality following SBW outbreaks and slightly underestimates current annual volume increment (CAI). In both mature and immature forests, the simulation model suggests a larger reduction in gross primary productivity (GPP) than in autotrophic respiration (Ra) at the same defoliation level when tree mortality was low. After an SBW outbreak, the growth release of surviving trees contributes to the recovery of annual net ecosystem productivity (NEP) based on forest age if mortality is not excessive. Overall, the TRIPLEX-Insect model is capable of simulating C dynamics of balsam fir following SBW disturbances and can be used as an efficient tool in forest insect management.

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Teng, Dexiong, Xuemin He, Lu Qin et Guanghui Lv. « Energy Balance Closure in the Tugai Forest in Ebinur Lake Basin, Northwest China ». Forests 12, n^o 2 (20 février 2021) : 243. http://dx.doi.org/10.3390/f12020243.

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A persistent problem in surface flux research is that turbulent fluxes observed by eddy covariance methods tend to be lower than the available energy. Using 7 years of eddy covariance flux observations in the Ebinur Lake National Wetland Nature Reserve (ELNWNR) in Xinjiang, Northwest China, this study analyzes the surface–atmosphere energy transfer characteristics at the station to explore variation characteristics of the energy flux and the energy balance closure (EBC), and the factors that influence EBC. The results show that: (1) diurnal and seasonal variations are observed in turbulent flux, available energy, and the partitioning of sensible and latent fluxes affected by environmental factors; (2) the degree of EBC varies significantly diurnally and seasonally, with EBC during the growing season significantly higher than during the dormant season; (3) due to the surface heterogeneity, EBC exhibits significant variations with wind direction that differ between the growing and dormant seasons; (4) environmental factors (e.g., vapor pressure deficit and air temperature) are important in limiting near-surface EBC, but they play a secondary role compared with the state of atmospheric motion. This study provides a basis for accurately assessing the material and energy exchanges between the desert Tugai forest ecosystem and the atmosphere.

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Wang, Xiaofei, Guang Zheng, Zengxin Yun et L. Monika Moskal. « Characterizing Tree Spatial Distribution Patterns Using Discrete Aerial Lidar Data ». Remote Sensing 12, n^o 4 (21 février 2020) : 712. http://dx.doi.org/10.3390/rs12040712.

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Tree spatial distribution patterns such as random, regular, and clustered play a crucial role in numerical simulations of carbon and water cycles and energy exchanges between forest ecosystems and the atmosphere. An efficient approach is needed to characterize tree spatial distribution patterns quantitatively. This study aims to employ increasingly available aerial laser scanning (ALS) data to capture individual tree locations and further characterize their spatial distribution patterns at the landscape or regional levels. First, we use the pair correlation function to identify the categories (i.e., random, regular, and clustered) of tree spatial distribution patterns, and then determine the unknown parameters of statistical models used for approximating each tree spatial distribution pattern using ALS-based metrics. After applying the proposed method in both natural and urban forest sites, our results show that ALS-based tree crown radii can capture 58%–77% (p < 0.001) variations of visual-based measurements depending on forest types and densities. The root mean squared errors (RMSEs) of ALS-based tree locations increase from 1.46 m to 2.51 m as the forest densities increasing. The Poisson, soft-core, and hybrid-Gibbs point processes are determined as the optimal models to approximate random, regular, and clustered tree spatial distribution patterns, respectively. This work provides a solid foundation for improving the simulation accuracy of forest canopy bidirectional reflectance distribution function (BRDF) and further obtain a better understanding of the processes of carbon and water cycles of forest ecosystems.

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Jackson, Toby D., Sarab Sethi, Ebba Dellwik, Nikolas Angelou, Amanda Bunce, Tim van Emmerik, Marine Duperat et al. « The motion of trees in the wind : a data synthesis ». Biogeosciences 18, n^o 13 (6 juillet 2021) : 4059–72. http://dx.doi.org/10.5194/bg-18-4059-2021.

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Abstract. Interactions between wind and trees control energy exchanges between the atmosphere and forest canopies. This energy exchange can lead to the widespread damage of trees, and wind is a key disturbance agent in many of the world's forests. However, most research on this topic has focused on conifer plantations, where risk management is economically important, rather than broadleaf forests, which dominate the forest carbon cycle. This study brings together tree motion time-series data to systematically evaluate the factors influencing tree responses to wind loading, including data from both broadleaf and coniferous trees in forests and open environments. We found that the two most descriptive features of tree motion were (a) the fundamental frequency, which is a measure of the speed at which a tree sways and is strongly related to tree height, and (b) the slope of the power spectrum, which is related to the efficiency of energy transfer from wind to trees. Intriguingly, the slope of the power spectrum was found to remain constant from medium to high wind speeds for all trees in this study. This suggests that, contrary to some predictions, damping or amplification mechanisms do not change dramatically at high wind speeds, and therefore wind damage risk is related, relatively simply, to wind speed. Conifers from forests were distinct from broadleaves in terms of their response to wind loading. Specifically, the fundamental frequency of forest conifers was related to their size according to the cantilever beam model (i.e. vertically distributed mass), whereas broadleaves were better approximated by the simple pendulum model (i.e. dominated by the crown). Forest conifers also had a steeper slope of the power spectrum. We interpret these finding as being strongly related to tree architecture; i.e. conifers generally have a simple shape due to their apical dominance, whereas broadleaves exhibit a much wider range of architectures with more dominant crowns.

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Majasalmi, Titta, Stephanie Eisner, Rasmus Astrup, Jonas Fridman et Ryan M. Bright. « An enhanced forest classification scheme for modeling vegetation–climate interactions based on national forest inventory data ». Biogeosciences 15, n^o 2 (18 janvier 2018) : 399–412. http://dx.doi.org/10.5194/bg-15-399-2018.

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Abstract. Forest management affects the distribution of tree species and the age class of a forest, shaping its overall structure and functioning and in turn the surface–atmosphere exchanges of mass, energy, and momentum. In order to attribute climate effects to anthropogenic activities like forest management, good accounts of forest structure are necessary. Here, using Fennoscandia as a case study, we make use of Fennoscandic National Forest Inventory (NFI) data to systematically classify forest cover into groups of similar aboveground forest structure. An enhanced forest classification scheme and related lookup table (LUT) of key forest structural attributes (i.e., maximum growing season leaf area index (LAImax), basal-area-weighted mean tree height, tree crown length, and total stem volume) was developed, and the classification was applied for multisource NFI (MS-NFI) maps from Norway, Sweden, and Finland. To provide a complete surface representation, our product was integrated with the European Space Agency Climate Change Initiative Land Cover (ESA CCI LC) map of present day land cover (v.2.0.7). Comparison of the ESA LC and our enhanced LC products (https://doi.org/10.21350/7zZEy5w3) showed that forest extent notably (κ = 0.55, accuracy 0.64) differed between the two products. To demonstrate the potential of our enhanced LC product to improve the description of the maximum growing season LAI (LAImax) of managed forests in Fennoscandia, we compared our LAImax map with reference LAImax maps created using the ESA LC product (and related cross-walking table) and PFT-dependent LAImax values used in three leading land models. Comparison of the LAImax maps showed that our product provides a spatially more realistic description of LAImax in managed Fennoscandian forests compared to reference maps. This study presents an approach to account for the transient nature of forest structural attributes due to human intervention in different land models.

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Zhu, Huajie, Mousong Wu, Fei Jiang, Michael Vossbeck, Thomas Kaminski, Xiuli Xing, Jun Wang, Weimin Ju et Jing M. Chen. « Assimilation of carbonyl sulfide (COS) fluxes within the adjoint-based data assimilation system – Nanjing University Carbon Assimilation System (NUCAS v1.0) ». Geoscientific Model Development 17, n^o 16 (30 août 2024) : 6337–63. http://dx.doi.org/10.5194/gmd-17-6337-2024.

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Abstract. Modeling and predicting changes in the function and structure of the terrestrial biosphere and its feedbacks to climate change strongly depends on our ability to accurately represent interactions of the carbon and water cycles and energy exchange. However, carbon fluxes, hydrological status, and energy exchange simulated by process-based terrestrial ecosystem models are subject to significant uncertainties, largely due to the poorly calibrated parameters. In this work, an adjoint-based data assimilation system (Nanjing University Carbon Assimilation System; NUCAS v1.0) was developed, which is capable of assimilating multiple observations to optimize process parameters of a satellite-data-driven ecosystem model – the Biosphere–atmosphere Exchange Process Simulator (BEPS). Data assimilation experiments were conducted to investigate the robustness of NUCAS and to test the feasibility and applicability of assimilating carbonyl sulfide (COS) fluxes from seven sites to enhance our understanding of stomatal conductance and photosynthesis. Results showed that NUCAS is able to achieve a consistent fit to COS observations across various ecosystems, including evergreen needleleaf forest, deciduous broadleaf forest, C3 grass, and C3 crop. Comparing model simulations with validation datasets, we found that assimilating COS fluxes notably improves the model performance in gross primary productivity and evapotranspiration, with average root-mean-square error (RMSE) reductions of 23.54 % and 16.96 %, respectively. We also showed that NUCAS is capable of constraining parameters through assimilating observations from two sites simultaneously and achieving a good consistency with single-site assimilation. Our results demonstrate that COS can provide constraints on parameters relevant to water, energy, and carbon processes with the data assimilation system and opens new perspectives for better understanding of the ecosystem carbon, water, and energy exchanges.

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Bright, Ryan M., Clara Antón-Fernández, Rasmus Astrup et Anders H. Strømman. « Empirical models of albedo transitions in managed boreal forests : analysis of performance and transportability ». Canadian Journal of Forest Research 45, n^o 2 (février 2015) : 195–206. http://dx.doi.org/10.1139/cjfr-2014-0132.

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Managing boreal forests for effective climate change mitigation requires comprehension of the full spectrum of climate regulation services that they provide, which includes both the storage of carbon and exchanges of heat and moisture with the atmosphere. It is increasingly recognized that surface albedo is the most important biogeophysical mechanism by which the boreal forest directly influences the global energy balance. Forest management decisions that influence age class and species distributions affect not only the carbon sink capacity, but also the albedo (and hence climate services) of the forested landscape. Disregarding albedo and how it is influenced by management decisions can have profound implications for the effectiveness of any climate change mitigation policy involving active forest management. Here, we explore, analyze, and compare the albedo predicted by simple empirical models with in situ and remotely sensed albedo observations in regions outside the region in which the models were originally developed (southeastern Norway), including boreal Canada and Europe. We find that the models are robust in their ability to predict the longer term interannual trends in the mean winter–summer albedo amplitude, the rapid albedo evolution in young stands, and the timing of seasonal transitions and weak with respect to capturing interannual albedo changes linked to seasonal climate variability and phenology.

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Fang, H. J., G. R. Yu, S. L. Cheng, T. H. Zhu, Y. S. Wang, J. H. Yan, M. Wang, M. Cao et M. Zhou. « Effects of multiple environmental factors on CO2 ; emission and CH4 ; uptake from old-growth forest soils ». Biogeosciences 7, n^o 1 (29 janvier 2010) : 395–407. http://dx.doi.org/10.5194/bg-7-395-2010.

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Abstract. To assess contribution of multiple environmental factors to carbon exchanges between the atmosphere and forest soils, four old-growth forests referred to as boreal coniferous forest, temperate needle-broadleaved mixed forest, subtropical evergreen broadleaved forest and tropical monsoon rain forest were selected along eastern China. In each old-growth forest, soil CO2 and CH4 fluxes were measured from 2003 to 2005 applying the static opaque chamber and gas chromatography technique. Soil temperature and moisture at the 10 cm depth were simultaneously measured with the greenhouse gas measurements. Inorganic N (NH4+-N and NO3−-N) in the 0–10 cm was determined monthly. From north to south, annual mean CO2 emission ranged from 18.09 ± 0.22 to 35.40 ± 2.24 Mg CO2 ha−1 yr−1 and annual mean CH4 uptake ranged from 0.04 ± 0.11 to 5.15 ± 0.96 kg CH4 ha−1 yr−1 in the four old-growth forests. Soil CO2 flux in the old-growth forests was mainly driven by soil temperature, followed by soil moisture and NO3−-N. Temperature sensitivity (Q10) of soil CO2 flux was lower at lower latitudes with high temperature and more precipitation, probably because of less soil organic carbon (SOC). Soil NO3− accumulation caused by environmental change was often accompanied by an increase in soil CO2 emission. In addition, soil CH4 uptake decreased with an increase in soil moisture. The response of soil CH4 flux to temperature was dependent upon the optimal value of soil temperature in each forest. Soil NH4+-N consumption tended to promote soil CH4 uptake in the old-growth forests, whereas soil NO3−-N accumulation was not conducive to CH4 oxidation in anaerobic condition. These results indicate that soil mineral N dynamics largely affects the soil gas fluxes of CO2 and CH4 in the old-growth forests, along with climate conditions.

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Murkute, Charuta, Mostafa Sayeed, Franz Pucha-Cofrep, Galo Carrillo-Rojas, Jürgen Homeier, Oliver Limberger, Andreas Fries, Jörg Bendix et Katja Trachte. « Turbulent Energy and Carbon Fluxes in an Andean Montane Forest—Energy Balance and Heat Storage ». Forests 15, n^o 10 (20 octobre 2024) : 1828. http://dx.doi.org/10.3390/f15101828.

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High mountain rainforests are vital in the global energy and carbon cycle. Understanding the exchange of energy and carbon plays an important role in reflecting responses to climate change. In this study, an eddy covariance (EC) measurement system installed in the high Andean Mountains of southern Ecuador was used. As EC measurements are affected by heterogeneous topography and the vegetation height, the main objective was to estimate the effect of the sloped terrain and the forest on the turbulent energy and carbon fluxes considering the energy balance closure (EBC) and the heat storage. The results showed that the performance of the EBC was generally good and estimated it to be 79.5%. This could be improved when the heat storage effect was considered. Based on the variability of the residuals in the diel, modifications in the imbalances were highlighted. Particularly, during daytime, the residuals were largest (56.9 W/m2 on average), with a clear overestimation. At nighttime, mean imbalances were rather weak (6.5 W/m2) and mostly positive while strongest underestimations developed in the transition period to morning hours (down to −100 W/m2). With respect to the Monin–Obukhov stability parameter ((z − d)/L) and the friction velocity (u*), it was revealed that the largest overestimations evolved in weak unstable and very stable conditions associated with large u* values. In contrast, underestimation was related to very unstable conditions. The estimated carbon fluxes were independently modelled with a non-linear regression using a light-response relationship and reached a good performance value (R2 = 0.51). All fluxes were additionally examined in the annual course to estimate whether both the energy and carbon fluxes resembled the microclimatological conditions of the study site. This unique study demonstrated that EC measurements provide valuable insights into land-surface–atmosphere interactions and contribute to our understanding of energy and carbon exchanges. Moreover, the flux data provide an important basis to validate coupled atmosphere ecosystem models.

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Toda, Motomu, Kumiko Takata, Naoyuki Nishimura, Masahito Yamada, Naoko Miki, Taro Nakai, Yuji Kodama et al. « Simulating seasonal and inter-annual variations in energy and carbon exchanges and forest dynamics using a process-based atmosphere–vegetation dynamics model ». Ecological Research 26, n^o 1 (14 octobre 2010) : 105–21. http://dx.doi.org/10.1007/s11284-010-0763-6.

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Graveline, Vincent, Manuel Helbig, Gabriel Hould Gosselin, Haley Alcock, Matteo Detto, Branden Walker, Philip Marsh et Oliver Sonnentag. « Surface-atmosphere energy exchanges and their effects on surface climate and atmospheric boundary layer characteristics in the forest-tundra ecotone in northwestern Canada ». Agricultural and Forest Meteorology 350 (mai 2024) : 109996. http://dx.doi.org/10.1016/j.agrformet.2024.109996.

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Zhao, Y., Y. Z. Wang, Z. H. Xu et L. Fu. « Impacts of prescribed burning on soil greenhouse gas fluxes in a suburban native forest of south-eastern Queensland, Australia ». Biogeosciences 12, n^o 21 (3 novembre 2015) : 6279–90. http://dx.doi.org/10.5194/bg-12-6279-2015.

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Abstract. Prescribed burning is a forest management practice that is widely used in Australia to reduce the risk of damaging wildfires. Prescribed burning can affect both carbon (C) and nitrogen (N) cycling in the forest and thereby influence the soil-atmosphere exchange of major greenhouse gases, i.e. carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). To quantify the impact of a prescribed burning (conducted on 27 May 2014) on greenhouse gas exchange and the potential controlling mechanisms, we carried out a series of field measurements before (August 2013) and after (August 2014 and November 2014) the fire. Gas exchange rates were determined in four replicate plots which were burned during the combustion and in another four adjacent unburned plots located in green islands, using a set of static chambers. Surface soil properties including temperature, pH, moisture, soil C and N pools were also determined either by in situ measurement or by analysing surface 10 cm soil samples. All of the chamber measurements indicated a net sink of atmospheric CH4, with mean CH4 uptake ranging from 1.15 to 1.99 mg m−2 d−1. Prescribed burning significantly enhanced CH4 uptake as indicated by the significant higher CH4 uptake rates in the burned plots measured in August 2014. In the following 3 months, the CH4 uptake rate was recovered to the pre-burning level. Mean CO2 emission from the forest soils ranged from 2721.76 to 7113.49 mg m−2 d−1. The effect of prescribed burning on CO2 emission was limited within the first 3 months, as no significant difference was observed between the burned and the adjacent unburned plots in both August and November 2014. The CO2 emissions showed more seasonal variations, rather than the effects of prescribed burning. The N2O emission in the plots was quite low, and no significant impact of prescribed burning was observed. The changes in understory plants and litter layers, surface soil temperature, C and N substrate availability and microbial activities, following the prescribed burning, were the factors that controlled the greenhouse gas exchanges. Our results suggested that the low-intensity prescribed burning would decrease soil CO2 emission and increase CH4 uptake, but this effect would be present within a relatively short period. Only slight changes in the surface soil properties during the combustion and very limited impacts of prescribed burning on the mineral soils supported the rapid recovery of the greenhouse gas exchange rates.

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Zhao, Y., Y. Z. Wang, Z. H. Xu et L. Fu. « Impacts of prescribed burning on soil greenhouse gas fluxes in a suburban native forest of south-eastern Queensland, Australia ». Biogeosciences Discussions 12, n^o 13 (9 juillet 2015) : 10679–706. http://dx.doi.org/10.5194/bgd-12-10679-2015.

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Abstract. Prescribed burning is a forest management practice that is widely used in Australia to reduce the risk of damaging wildfires. It can affect both carbon (C) and nitrogen (N) cycling in the forest and thereby influence the soil–atmosphere exchange of major greenhouse gases, i.e. carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). To quantify the impact of a prescribed burning (conducted on 27 May 2014) on greenhouse gas exchange and the potential controlling mechanisms, we carried out a series of field measurements before (August 2013) and after (August 2014 and November 2014) the fire. Gas exchange rates were determined at 4 replicate sites which were burned during the combustion and another 4 adjacent unburned sites located in green islands, using a set of static chambers. Surface soil properties including temperature, pH, moisture, soil C and N pools were also determined either by in situ measurement or by analysing surface 10 cm soil samples. All of the chamber measurements indicated a net sink of atmospheric CH4, with mean CH4 uptake ranging from 1.15 to 1.99 mg m−2 day−1. The burning significantly enhanced CH4 uptake as indicated by the significant higher CH4 uptake rates at the burned sites measured in August 2014. While within the next 3 months the CH4 uptake rate was recovered to pre-burning levels. Mean CO2 emission from forest soils ranged from 2721.76 to 7113.49 mg m−2 day−1. The effect of prescribed burning on CO2 emission was limited within the first 3 months, as no significant difference was observed between the burned and the adjacent unburned sites in both August and November 2014. The temporal dynamics of the CO2 emission presented more seasonal variations, rather than burning effects. The N2O emission at the studied sites was quite low, and no significant impact of burning was observed. The changes in understory plants and litter layers, surface soil temperature, C and N substrate availability and microbial activities, resulting from the burning, were the factors that controlled the greenhouse gas exchanges. Our results suggested that the low intensity prescribed burning would decrease soil CO2 emission and increase CH4 uptake, however, this effect would be present within a relative short period. Only slight changes in the surface soil during the combustion and very limited damages in the mineral soils supported the quick recovery of the greenhouse gas exchange rates.

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Smallman, T. L., M. Williams et J. B. Moncrieff. « Can seasonal and interannual variation in landscape CO2 ; fluxes be detected by atmospheric observations of CO2 ; concentrations made at a tall tower ? » Biogeosciences Discussions 10, n^o 8 (27 août 2013) : 14301–31. http://dx.doi.org/10.5194/bgd-10-14301-2013.

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Abstract. The Weather Research and Forecasting (WRF) meteorological model has been coupled to the Soil Plant Atmosphere (SPA) terrestrial ecosystem model, hereafter known as WRF-SPA. SPA generates realistic land-atmosphere exchanges through fully coupled hydrological, carbon and energy cycles. Here we have used WRF-SPA to investigate regional scale observations of atmospheric CO2 concentrations made over a multi-annual period from a tall tower in Scotland. WRF-SPA realistically models both seasonal and daily cycles, predicting CO2 at the tall tower (R2 = 0.67, RMSE = 3.5 ppm, bias = 0.58 ppm), indicating realistic transport, and appropriate source sink distribution and magnitude of CO2 exchange. We have highlighted a consistent post harvest increase in model-observation residuals in atmospheric CO2 concentrations. This increase in model-observation residuals post harvest is likely related to a lack of an appropriate representation of uncultivated components (~ 36% of agricultural holding in Scotland) of agricultural land (e.g., hedgerows and forest patches) which continue to photosynthesise after the crop has been harvested. Through the use of ecosystem specific CO2 tracers we have shown that tall tower observations here do not detect a representative fraction of Scotland's ecosystem CO2 uptake. Cropland CO2 uptake is the dominant ecosystem signal detected at the tall tower, consistent with the dominance of cropland in the area surrounding the tower. However cropland is over-represented in the atmospheric CO2 concentrations simulated to be at the tall tower, relative to the simulated surface cropland CO2 uptake. Observations made at the tall tower were able to detect seasonal variation in ecosystem CO2 uptake, however a majority of variation was only detected for croplands. We have found evidence that interannual variation in weather has a greater impact than interannual variation of the simulated land surface CO2 exchange on tall tower observations for the simulated years. This highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude.

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Nguyen, Vinh Xuan, Carlos P. Guerra Torres, Shilpi Yadav, Marian Pavelka et Michal V. Marek. « Wind characteristics of CzeCOS’s ecosystem station Bílý Kříž ». Beskydy 10, n^o 1-2 (2017) : 33–40. http://dx.doi.org/10.11118/beskyd201710010033.

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Eddy-covariance is a direct and accurate method to measure exchanges of greenhouse gases and energy between ecosystems and the atmosphere under good turbulent mixing conditions. Calm conditions can affect the accuracy of the eddy-covariance measurements by potential gas buildup below the measurement height. This study characterizes wind patterns and calm periods at Bílý Kříž Ecosystem Research Station, using four-year (2010-2013) wind data measured on an eddy-covariance tower at the site, located in Beskids Mountains, Czech Republic. The site is covered by young, dense Norway spruce forest on a 12.5° slope facing South. The results show that the prevailing wind direction was from S to SW direction (55 % frequency of occurrence), and to a much lesser extent from N, NE and NW but including the strongest winds above 12 m s-1, possibly during gale or storm events. Calm condition (u < 1 m s-1) accounted for 34 % of year time. Summer and Spring were the calmest seasons. Occurrence frequencies of calm conditions for the six-month periods from May to October (plant growing season) were higher than those for the remaining parts of the year (on average 39 % vs 28 % respectively). One should be aware of the calm periods in May-October when processing eddy-covariance data, since it is the time period of most contribution of forest ecosystem as a sink of CO2.

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Bannister, Edward J., Mike Jesson, Nicholas J. Harper, Kris M. Hart, Giulio Curioni, Xiaoming Cai et A. Rob MacKenzie. « Residence times of air in a mature forest : observational evidence from a free-air CO₂ enrichment experiment ». Atmospheric Chemistry and Physics 23, n^o 3 (13 février 2023) : 2145–65. http://dx.doi.org/10.5194/acp-23-2145-2023.

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Abstract. In forests, the residence time of air – the inverse of first-order exchange rates – influences in-canopy chemistry and the exchanges of momentum, energy, and mass with the surrounding atmosphere. Accurate estimates are needed for chemical investigations of reactive trace species, such as volatile organic compounds, some of whose chemical lifetimes are on the order of average residence times. However, very few observational residence-time estimates have been reported. Little is known about even the basic statistics of real-world residence times or how they are influenced by meteorological variables such as turbulence or atmospheric stability. Here, we report opportunistic investigations of residence time of air in a free-air carbon dioxide enrichment (FACE) facility in a mature, broadleaf deciduous forest with canopy height of hc≈25 m. Using nearly 50 million FACE observations, we find that median daytime residence times in the tree crowns range from around 70 s when the trees are in leaf to just over 34 s when they are not. Residence times increase with increasing atmospheric stability, as does the spread around their central value. Residence times scale approximately with the reciprocal of the friction velocity, u∗. During some calm evenings in the growing season, we observe distinctly different behaviour: pooled air being sporadically and unpredictably vented – evidenced by sustained increases in CO2 concentration – when intermittent turbulence penetrates the canopy. In these conditions, the concept of a residence time is less clearly defined. Parameterisations available in the literature underestimate turbulent exchange in the upper half of forest crowns and overestimate the frequency of long residence times. Robust parameterisations of residence times (or, equivalently, fractions of emissions escaping the canopy) may be generated from inverse-gamma distributions, with the parameters 1.4≤α≤1.8 and β=hc/u∗ estimated from widely measured flow variables. In this case, the mean value for τ becomes formally defined as τ‾=β/(α-1). For species released in the canopy during the daytime, chemical transformations are unlikely unless the reaction timescale is on the order of a few minutes or less.

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Rawlins, M. A., A. D. McGuire, J. K. Kimball, P. Dass, D. Lawrence, E. Burke, X. Chen et al. « Assessment of model estimates of land–atmosphere CO2 ; exchange across Northern Eurasia ». Biogeosciences Discussions 12, n^o 3 (3 février 2015) : 2257–305. http://dx.doi.org/10.5194/bgd-12-2257-2015.

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Abstract. A warming climate is altering land–atmosphere exchanges of carbon, with a potential for increased vegetation productivity as well as the mobilization of permafrost soil carbon stores. Here we investigate land–atmosphere carbon dioxide (CO2) dynamics through analysis of net ecosystem productivity (NEP) and its component fluxes of gross primary productivity (GPP) and ecosystem respiration (ER) and soil carbon residence time, simulated by a set of land surface models (LSMs) over a region spanning the drainage basin of northern Eurasia. The retrospective simulations were conducted over the 1960–2009 record and at 0.5° resolution, which is a scale common among many global carbon and climate model simulations. Model performance benchmarks were drawn from comparisons against both observed CO2 fluxes derived from site-based eddy covariance measurements as well as regional-scale GPP estimates based on satellite remote sensing data. The site-based comparisons show the timing of peak GPP to be well simulated. Modest overestimates in model GPP and ER are also found, which are relatively higher for two boreal forest validation sites than the two tundra sites. Across the suite of model simulations, NEP increases by as little as 0.01 to as much as 0.79 g C m−2 yr−2, equivalent to 3 to 340% of the respective model means, over the analysis period. For the multimodel average the increase is 135% of the mean from the first to last ten years of record (1960–1969 vs 2000–2009), with a weakening CO2 sink over the latter decades. Vegetation net primary productivity increased by 8 to 30% from the first to last ten years, contributing to soil carbon storage gains, while model mean residence time for soil organic carbon decreased by 10% (−5 to −16%). This suggests that inputs to the soil carbon pool exceeded losses, resulting in a net gain amid a decrease in residence time. Our analysis points to improvements in model elements controlling vegetation productivity and soil respiration as being needed for reducing uncertainty in land–atmosphere CO2 exchange. These advances require collection of new field data on vegetation and soil dynamics, the development of benchmarking datasets from measurements and remote sensing observations, and investments in future model development and intercomparison studies. Resulting improvements in parameterizations and processes driving productivity and soil respiration rates will increase confidence in model estimates of net CO2 exchange, component carbon fluxes, and underlying drivers of change across the northern high latitudes.

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Soudani, Kamel, Nicolas Delpierre, Daniel Berveiller, Gabriel Hmimina, Jean-Yves Pontailler, Lou Seureau, Gaëlle Vincent et Éric Dufrêne. « A survey of proximal methods for monitoring leaf phenology in temperate deciduous forests ». Biogeosciences 18, n^o 11 (7 juin 2021) : 3391–408. http://dx.doi.org/10.5194/bg-18-3391-2021.

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Abstract. Tree phenology is a major driver of forest–atmosphere mass and energy exchanges. Yet, tree phenology has rarely been monitored in a consistent way throughout the life of a flux-tower site. Here, we used seasonal time series of ground-based NDVI (Normalized Difference Vegetation Index), RGB camera GCC (greenness chromatic coordinate), broadband NDVI, LAI (leaf area index), fAPAR (fraction of absorbed photosynthetic active radiation), CC (canopy closure), fRvis (fraction of reflected radiation) and GPP (gross primary productivity) to predict six phenological markers detecting the start, middle and end of budburst and of leaf senescence in a temperate deciduous forest using an asymmetric double sigmoid function (ADS) fitted to the time series. We compared them to observations of budburst and leaf senescence achieved by field phenologists over a 13-year period. GCC, NDVI and CC captured the interannual variability of spring phenology very well (R2>0.80) and provided the best estimates of the observed budburst dates, with a mean absolute deviation (MAD) of less than 4 d. For the CC and GCC methods, mid-amplitude (50 %) threshold dates during spring phenological transition agreed well with the observed phenological dates. For the NDVI-based method, on average, the mean observed date coincides with the date when NDVI reaches 25 % of its amplitude of annual variation. For the other methods, MAD ranges from 6 to 17 d. The ADS method used to derive the phenological markers provides the most biased estimates for the GPP and GCC. During the leaf senescence stage, NDVI- and CC-derived dates correlated significantly with observed dates (R2=0.63 and 0.80 for NDVI and CC, respectively), with an MAD of less than 7 d. Our results show that proximal-sensing methods can be used to derive robust phenological metrics. They can be used to retrieve long-term phenological series at eddy covariance (EC) flux measurement sites and help interpret the interannual variability and trends of mass and energy exchanges.

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Beringer, J., L. B. Hutley, N. J. Tapper, A. Coutts, A. Kerley et A. P. O'Grady. « Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia ». International Journal of Wildland Fire 12, n^o 4 (2003) : 333. http://dx.doi.org/10.1071/wf03023.

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Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post-fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes. These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation.

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Xin, Q., P. Gong et W. Li. « Modeling photosynthesis of discontinuous plant canopies by linking the Geometric Optical Radiative Transfer model with biochemical processes ». Biogeosciences 12, n^o 11 (5 juin 2015) : 3447–67. http://dx.doi.org/10.5194/bg-12-3447-2015.

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Abstract. Modeling vegetation photosynthesis is essential for understanding carbon exchanges between terrestrial ecosystems and the atmosphere. The radiative transfer process within plant canopies is one of the key drivers that regulate canopy photosynthesis. Most vegetation cover consists of discrete plant crowns, of which the physical observation departs from the underlying assumption of a homogenous and uniform medium in classic radiative transfer theory. Here we advance the Geometric Optical Radiative Transfer (GORT) model to simulate photosynthesis activities for discontinuous plant canopies. We separate radiation absorption into two components that are absorbed by sunlit and shaded leaves, and derive analytical solutions by integrating over the canopy layer. To model leaf-level and canopy-level photosynthesis, leaf light absorption is then linked to the biochemical process of gas diffusion through leaf stomata. The canopy gap probability derived from GORT differs from classic radiative transfer theory, especially when the leaf area index is high, due to leaf clumping effects. Tree characteristics such as tree density, crown shape, and canopy length affect leaf clumping and regulate radiation interception. Modeled gross primary production (GPP) for two deciduous forest stands could explain more than 80% of the variance of flux tower measurements at both near hourly and daily timescales. We demonstrate that ambient CO2 concentrations influence daytime vegetation photosynthesis, which needs to be considered in biogeochemical models. The proposed model is complementary to classic radiative transfer theory and shows promise in modeling the radiative transfer process and photosynthetic activities over discontinuous forest canopies.

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Strasser, Ulrich, Michael Warscher et Glen E. Liston. « Modeling Snow–Canopy Processes on an Idealized Mountain ». Journal of Hydrometeorology 12, n^o 4 (1 août 2011) : 663–77. http://dx.doi.org/10.1175/2011jhm1344.1.

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Abstract Snow interception in a coniferous forest canopy is an important hydrological feature, producing complex mass and energy exchanges with the surrounding atmosphere and the snowpack below. Subcanopy snowpack accumulation and ablation depends on the effects of canopy architecture on meteorological conditions and on interception storage by stems, branches, and needles. Mountain forests are primarily composed of evergreen conifer species that retain their needles throughout the year and hence intercept snow efficiently during winter. Canopy-intercepted snow can melt, fall to the ground, and/or sublimate into the air masses above and within the canopy. To improve the understanding of snow–canopy interception processes and the associated influences on the snowpack below, a series of model experiments using a detailed, physically based snow–canopy and snowpack evolution model [Alpine Multiscale Numerical Distributed Simulation Engine (AMUNDSEN)] driven with observed meteorological forcing was conducted. A cone-shaped idealized mountain covered with a geometrically regular pattern of coniferous forest stands and clearings was constructed. The model was applied for three winter seasons with different snowfall intensities and distributions. Results show the effects of snow–canopy processes and interactions on the pattern of ground snow cover, its duration, and the amount of meltwater release, in addition to showing under what conditions the protective effect of a forest canopy overbalances the reduced accumulation of snow on the ground. The simulations show considerable amounts of canopy-intercepted snowfall can sublimate, leading to reduced snow accumulation beneath the forest canopy. In addition, the canopy produces a shadowing effect beneath the trees that leads to reduced radiative energy reaching the ground, reduced below-canopy snowmelt rates, and increased snow-cover duration relative to nonforested areas. During snow-rich winters, the shadowing effect of the canopy dominates and snow lasts longer inside the forest than in the open, but during winters with little snow, snow sublimation losses dominate and snow lasts longer in the open areas than inside the forest. Because of the strong solar radiation influence on snowmelt rates, the details of these relationships vary for northern and southern radiation exposures and time of year. In early and high winter, the radiation protection effect of shadowing by the canopy is small. If little snow is available, an intermittent melt out of the snow cover inside the forest can occur. In late winter and spring, the shadowing effect becomes more efficient and snowmelt is delayed relative to nonforested areas.

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Xin, Q., P. Gong et W. Li. « Modeling photosynthesis of discontinuous plant canopies by linking Geometric Optical Radiative Transfer model with biochemical processes ». Biogeosciences Discussions 12, n^o 4 (27 février 2015) : 3675–729. http://dx.doi.org/10.5194/bgd-12-3675-2015.

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Abstract. Modeling vegetation photosynthesis is essential for understanding carbon exchanges between terrestrial ecosystems and the atmosphere. The radiative transfer process within plant canopies is one of the key drivers that regulate canopy photosynthesis. Most vegetation cover consists of discrete plant crowns, of which the physical observation departs from the underlying assumption of a homogenous and uniform medium in classic radiative transfer theory. Here we advance the Geometric Optical Radiative Transfer (GORT) model to simulate photosynthesis activities for discontinuous plant canopies. We separate radiation absorption into two components that are absorbed by sunlit and shaded leaves, and derive analytical solutions by integrating over the canopy layer. To model leaf-level and canopy-level photosynthesis, leaf light absorption is then linked to the biochemical process of gas diffusion through leaf stomata. The canopy gap probability derived from GORT differs from classic radiative transfer theory, especially when the leaf area index is high, due to leaf clumping effects. Tree characteristics such as tree density, crown shape, and canopy length affect leaf clumping and regulate radiation interception. Modeled gross primary production (GPP) for two deciduous forest stands could explain more than 80% of the variance of flux tower measurements at both near hourly and daily time scales. We also demonstrate that the ambient CO2 concentration influences daytime vegetation photosynthesis, which needs to be considered in state-of-the-art biogeochemical models. The proposed model is complementary to classic radiative transfer theory and shows promise in modeling the radiative transfer process and photosynthetic activities over discontinuous forest canopies.

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Gathany, Mark A., et Ingrid C. Burke. « Post-fire soil fluxes of CO2, CH4 and N2O along the Colorado Front Range ». International Journal of Wildland Fire 20, n^o 7 (2011) : 838. http://dx.doi.org/10.1071/wf09135.

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Wildfires affect Rocky Mountain ecosystems across a wide range of spatial and temporal scales. Many of the resulting changes are greatest for environmental factors, such as substrate and microclimate that control exchanges of greenhouse gases. We investigated this link to understand how time since fire influences the cycling of these gases through ponderosa pine forests. We measured and compared trace gas flux rates between recently burned sites and topographical aspects (north- and south-facing slopes). We calculated the ability of five factors (soil temperature, soil moisture, fire severity, aspect and time since fire) to describe the variability in the flux rates. Our study revealed that carbon dioxide (CO2) fluxes were significantly different between sites; however, methane (CH4) uptake was not different between sites or aspects. Nitrous oxide (N2O) fluxes had a significant interaction between site and aspect. Using a likelihood approach, we determined the strength of support in the data for model combinations of five variables. Of these, the single variable models soil moisture, time since fire and severity best described the CO2, CH4, and N2O flux data respectively. Our data show that following a forest fire in the Colorado Front Range, >98% of the global warming potential of the measured soil–atmosphere fluxes is contributed by the soil CO2 flux.

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Grant, R. F., T. A. Black, G. den Hartog, J. A. Berry, H. H. Neumann, P. D. Blanken, P. C. Yang, C. Russell et I. A. Nalder. « Diurnal and annual exchanges of mass and energy between an aspen-hazelnut forest and the atmosphere : Testing the mathematical model Ecosys with data from the BOREAS experiment ». Journal of Geophysical Research : Atmospheres 104, n^o D22 (1 novembre 1999) : 27699–717. http://dx.doi.org/10.1029/1998jd200117.

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WADA, Ryuichi, Seiichiro YONEMURA, Akira TANI et Mizuo KAJINO. « Review : Exchanges of O3, NO, and NO2 ; between forest ecosystems and the atmosphere ». Journal of Agricultural Meteorology 79, n^o 1 (10 janvier 2023) : 38–48. http://dx.doi.org/10.2480/agrmet.d-22-00023.

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Deirmendjian, Loris, Denis Loustau, Laurent Augusto, Sébastien Lafont, Christophe Chipeaux, Dominique Poirier et Gwenaël Abril. « Hydro-ecological controls on dissolved carbon dynamics in groundwater and export to streams in a temperate pine forest ». Biogeosciences 15, n^o 2 (1 février 2018) : 669–91. http://dx.doi.org/10.5194/bg-15-669-2018.

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Abstract. We studied the export of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from forested shallow groundwater to first-order streams, based on groundwater and surface water sampling and hydrological data. The selected watershed was particularly convenient for such study, with a very low slope, with pine forest growing on sandy permeable podzol and with hydrology occurring exclusively through drainage of shallow groundwater (no surface runoff). A forest plot was instrumented for continuous eddy covariance measurements of precipitation, evapotranspiration, and net ecosystem exchanges of sensible and latent heat fluxes as well as CO2 fluxes. Shallow groundwater was sampled with three piezometers located in different plots, and surface waters were sampled in six first-order streams; river discharge and drainage were modeled based on four gauging stations. On a monthly basis and on the plot scale, we found a good consistency between precipitation on the one hand and the sum of evapotranspiration, shallow groundwater storage and drainage on the other hand. DOC and DIC stocks in groundwater and exports to first-order streams varied drastically during the hydrological cycle, in relation with water table depth and amplitude. In the groundwater, DOC concentrations were maximal in winter when the water table reached the superficial organic-rich layer of the soil. In contrast, DIC (in majority excess CO2) in groundwater showed maximum concentrations at low water table during late summer, concomitant with heterotrophic conditions of the forest plot. Our data also suggest that a large part of the DOC mobilized at high water table was mineralized to DIC during the following months within the groundwater itself. In first-order streams, DOC and DIC followed an opposed seasonal trend similar to groundwater but with lower concentrations. On an annual basis, leaching of carbon to streams occurred as DIC and DOC in similar proportion, but DOC export occurred in majority during short periods of the highest water table, whereas DIC export was more constant throughout the year. Leaching of forest carbon to first-order streams represented a small portion (approximately 2 %) of the net land CO2 sink at the plot. In addition, approximately 75 % of the DIC exported from groundwater was not found in streams, as it returned very fast to the atmosphere through CO2 degassing.

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Chen, Yiying, James Ryder, Vladislav Bastrikov, Matthew J. McGrath, Kim Naudts, Juliane Otto, Catherine Ottlé et al. « Evaluating the performance of land surface model ORCHIDEE-CAN v1.0 on water and energy flux estimation with a single- and multi-layer energy budget scheme ». Geoscientific Model Development 9, n^o 9 (2 septembre 2016) : 2951–72. http://dx.doi.org/10.5194/gmd-9-2951-2016.

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Abstract. Canopy structure is one of the most important vegetation characteristics for land–atmosphere interactions, as it determines the energy and scalar exchanges between the land surface and the overlying air mass. In this study we evaluated the performance of a newly developed multi-layer energy budget in the ORCHIDEE-CAN v1.0 land surface model (Organising Carbon and Hydrology In Dynamic Ecosystems – CANopy), which simulates canopy structure and can be coupled to an atmospheric model using an implicit coupling procedure. We aim to provide a set of acceptable parameter values for a range of forest types. Top-canopy and sub-canopy flux observations from eight sites were collected in order to conduct this evaluation. The sites crossed climate zones from temperate to boreal and the vegetation types included deciduous, evergreen broad-leaved and evergreen needle-leaved forest with a maximum leaf area index (LAI; all-sided) ranging from 3.5 to 7.0. The parametrization approach proposed in this study was based on three selected physical processes – namely the diffusion, advection, and turbulent mixing within the canopy. Short-term sub-canopy observations and long-term surface fluxes were used to calibrate the parameters in the sub-canopy radiation, turbulence, and resistance modules with an automatic tuning process. The multi-layer model was found to capture the dynamics of sub-canopy turbulence, temperature, and energy fluxes. The performance of the new multi-layer model was further compared against the existing single-layer model. Although the multi-layer model simulation results showed few or no improvements to both the nighttime energy balance and energy partitioning during winter compared with a single-layer model simulation, the increased model complexity does provide a more detailed description of the canopy micrometeorology of various forest types. The multi-layer model links to potential future environmental and ecological studies such as the assessment of in-canopy species vulnerability to climate change, the climate effects of disturbance intensities and frequencies, and the consequences of biogenic volatile organic compound (BVOC) emissions from the terrestrial ecosystem.

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Tang, Senlin, Hong Wang, Yao Feng, Qinghua Liu, Tingting Wang, Wenbin Liu et Fubao Sun. « Random Forest-Based Reconstruction and Application of the GRACE Terrestrial Water Storage Estimates for the Lancang-Mekong River Basin ». Remote Sensing 13, n^o 23 (28 novembre 2021) : 4831. http://dx.doi.org/10.3390/rs13234831.

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Terrestrial water storage (TWS) is a critical variable in the global hydrological cycle. The TWS estimates derived from the Gravity Recovery and Climate Experiment (GRACE) allow us to better understand water exchanges between the atmosphere, land surface, sea, and glaciers. However, missing historical (pre-2002) GRACE data limit their further application. In this study, we developed a random forest (RF) model to reconstruct the monthly terrestrial water storage anomaly (TWSA) time series using Global Land Data Assimilation System (GLDAS) and Climatic Research Unit (CRU) data for the Lancang-Mekong River basin. The results show that the RF-built TWSA time series agrees well with the GRACE TWSA time series for 2003–2014, showing that correlation coefficients (R) of 0.97 and 0.90 at the basin and grid scales, respectively, which demonstrates the reliability of the RF model. Furthermore, this method is used to reconstruct the historical TWSA time series for 1980–2002. Moreover, the discharge can be obtained by subtracting the evapotranspiration (ET) and RF-built terrestrial water storage change (TWSC) from the precipitation. The comparison between the discharge calculated from the water balance method and the observed discharge showed significant consistency, with a correlation coefficient of 0.89 for 2003–2014 but a slightly lower correlation coefficient (0.86) for 1980–2002. The methods and findings in this study can provide an effective means of reconstructing the TWSA and discharge time series in basins with sparse hydrological data.

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Nousu, Jari-Pekka, Kersti Leppä, Hannu Marttila, Pertti Ala-aho, Giulia Mazzotti, Terhikki Manninen, Mika Korkiakoski, Mika Aurela, Annalea Lohila et Samuli Launiainen. « Multi-scale soil moisture data and process-based modeling reveal the importance of lateral groundwater flow in a subarctic catchment ». Hydrology and Earth System Sciences 28, n^o 20 (24 octobre 2024) : 4643–66. http://dx.doi.org/10.5194/hess-28-4643-2024.

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Abstract. Soil moisture plays a key role in soil nutrient and carbon cycling; plant productivity; and energy, water, and greenhouse gas exchanges between the land and the atmosphere. The knowledge on drivers of spatiotemporal soil moisture dynamics in subarctic landscapes is limited. In this study, we used the Spatial Forest Hydrology (SpaFHy) model, in situ soil moisture data, and Sentinel-1 synthetic aperture radar (SAR)-based soil moisture estimates to explore spatiotemporal controls of soil moisture in a subarctic headwater catchment in northwestern Finland. The role of groundwater dynamics and lateral flow in soil moisture was studied through three groundwater model conceptualizations: (i) omission of groundwater storage and lateral flow, (ii) conceptual TOPMODEL approach based on topographic wetness index, and (iii) explicit 2D lateral groundwater flow. The model simulations were compared against continuous point soil moisture measurements, distributed manual measurements, and novel SAR-based soil moisture estimates available at high spatial and temporal resolutions. Based on model scenarios and model–data comparisons, we assessed when and where the lateral groundwater flow shapes shallow soil moisture and under which conditions soil moisture variability is driven more by local ecohydrology, i.e., the balance of infiltration, drainage, and evapotranspiration. The choice of groundwater flow model was shown to have a strong impact on modeled soil moisture dynamics within the catchment. All model conceptualizations captured the observed soil moisture dynamics in the upland forests, but accounting for the lateral groundwater flow was necessary to reproduce the saturated conditions common in the peatlands and occasionally in lowland forest grid cells. We further highlight the potential of integrating multi-scale observations with land surface and hydrological models. The results have implications for ecohydrological and biogeochemical processes, as well as for modeling hydrology and Earth system feedbacks in subarctic and boreal environments.

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