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1
Du, Enzai, et Yang Tang. « Distinct Climate Effects on Dahurian Larch Growth at an Asian Temperate-Boreal Forest Ecotone and Nearby Boreal Sites ». Forests 13, no 1 (26 décembre 2021) : 27. http://dx.doi.org/10.3390/f13010027.
Texte intégralRésumé :
Climate change is exerting profound impacts on the structure and function of global boreal forest. Compared with their northern counterparts, trees growing at the southern boreal forest and the temperate-boreal forest ecotone likely show distinct responses to climate change. Based on annual basal areal increment (BAI) of Dahurian larch (Larix gmelinii Rupr.) plantations with similar ages, tree densities and soil nutrient conditions, we investigated the tree growth responses to inter-annual climate variations at an Asian temperate-boreal forest ecotone and nearby boreal sites in northeast China. Annual BAI changed nonlinearly with cambial age in the form of a lognormal curve. The maximum annual BAI showed no significant difference between the two bioregions, while annual BAI peaked at an elder age at the boreal-temperate forest ecotone. After eliminating the age associated trend, conditional regression analyses indicate that residual BAI at the boreal sites increased significantly with higher growing-season mean nighttime minimum temperature and non-growing-season precipitation, but decreased significantly with higher growing-season mean daytime maximum temperature during the past three decades (1985–2015). In contrast, residual BAI at the boreal-temperate forest ecotone only showed a positive and weak response to inter-annual variations of growing-season precipitation. These findings suggest distinct effects of inter-annual climate variation on the growth of boreal trees at the temperate-boreal forest ecotone in comparison to the southern boreal regions, and highlight future efforts to elucidate the key factors that regulate the growth ofthe southernmost boreal trees.
2
Frelich, Lee E., Rebecca A. Montgomery et Peter B. Reich. « Seven Ways a Warming Climate Can Kill the Southern Boreal Forest ». Forests 12, no 5 (29 avril 2021) : 560. http://dx.doi.org/10.3390/f12050560.
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The southern boreal forests of North America are susceptible to large changes in composition as temperate forests or grasslands may replace them as the climate warms. A number of mechanisms for this have been shown to occur in recent years: (1) Gradual replacement of boreal trees by temperate trees through gap dynamics; (2) Sudden replacement of boreal overstory trees after gradual understory invasion by temperate tree species; (3) Trophic cascades causing delayed invasion by temperate species, followed by moderately sudden change from boreal to temperate forest; (4) Wind and/or hail storms removing large swaths of boreal forest and suddenly releasing temperate understory trees; (4) Compound disturbances: wind and fire combination; (5) Long, warm summers and increased drought stress; (6) Insect infestation due to lack of extreme winter cold; (7) Phenological disturbance, due to early springs, that has the potential to kill enormous swaths of coniferous boreal forest within a few years. Although most models project gradual change from boreal forest to temperate forest or savanna, most of these mechanisms have the capability to transform large swaths (size range tens to millions of square kilometers) of boreal forest to other vegetation types during the 21st century. Therefore, many surprises are likely to occur in the southern boreal forest over the next century, with major impacts on forest productivity, ecosystem services, and wildlife habitat.
3
McCarthy, J. « Gap dynamics of forest trees : A review with particular attention to boreal forests ». Environmental Reviews 9, no 1 (1 janvier 2001) : 1–59. http://dx.doi.org/10.1139/a00-012.
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Small-scale gap disturbance in forests is reviewed. Caused by the death of individual or multiple trees with subsequent fall from the canopy, gaps have been extensively studied in temperate deciduous and tropical forests for the past 20 years. This review considers much of this research with a view to assessing the importance of gap disturbance in boreal forests. Because of the ubiquity of large-scale, stand-initiating disturbances such as landscape-level fires, epidemic insect outbreaks, and periodic extensive windthrow events, gap processes in boreal forests have received little attention. Research in the Scandinavian and Russian boreal forest, as well as in high-altitude boreal "outliers" found in Japan and the United States, is showing that gap disturbance determines forest structure and processes to a greater extent than previously assumed. Boreal forests dominated by the shade-tolerant fir (Abies) spruce (Picea) complex are particularly well-adapted to the development of long-term, old-growth continuity in the absence of large-scale disturbance. Key words: gap dynamics, disturbance, boreal forests, temperate forests, tropical forests, silviculture.
4
Reich, Peter B., Kerrie M. Sendall, Artur Stefanski, Xiaorong Wei, Roy L. Rich et Rebecca A. Montgomery. « Boreal and temperate trees show strong acclimation of respiration to warming ». Nature 531, no 7596 (mars 2016) : 633–36. http://dx.doi.org/10.1038/nature17142.
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Bugmann, Harald. « Functional types of trees in temperate and boreal forests : classification and testing ». Journal of Vegetation Science 7, no 3 (juin 1996) : 359–70. http://dx.doi.org/10.2307/3236279.
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Machar, Ivo, Martin Schlossarek, Vilem Pechanec, Lubos Uradnicek, Ludek Praus et Ahmet Sıvacıoğlu. « Retention Forestry Supports Bird Diversity in Managed, Temperate Hardwood Floodplain Forests ». Forests 10, no 4 (1 avril 2019) : 300. http://dx.doi.org/10.3390/f10040300.
Texte intégralRésumé :
The retention forestry approach is considered as one of the potentially effective tools for sustainable forest management for conservation of biodiversity in managed temperate and boreal forests. Retention of old-growth forest structures (e.g., very large old living trees) in forest stands during clear-cutting provides maintenance of key habitats for many old-growth forest interior-species. Most of ecological studies on green tree retention (GTR) consequences for biodiversity have been focused on birds. However, the long-term studies of GTR impacts on forest birds are very poor. In this paper, we focused on assessment of the long-term consequences of leaving legacy oak trees on the cut areas for bird diversity 18–22 years after clear-cutting in managed temperate European hardwood floodplain forests. Results based on bird counting using mapping of bird nesting territories revealed a key importance of legacy oak trees for maintaining bird diversity in the study area. These results are widely applicable for managed temperate hardwood forests with serious dominance of oak (Quercus sp.) in forest stands. Legacy oak trees in this habitat type are keystone structures for bird diversity. Retention approach focused on these trees is potentially an important conservation tool for preserving forest bird diversity and other associated species in temperate hardwood forests managed by clear-cutting.
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Baas, Pieter, et Fritz H. Schweingruber. « Ecological Trends in the Wood Anatomy of Trees, Shrubs and Climbers from Europe ». IAWA Journal 8, no 3 (1987) : 245–74. http://dx.doi.org/10.1163/22941932-90001053.
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Ecological trends for occurrence of certain vessel, tracheid and fibre characteristics. have been analysed for 505 species (belonging to 221 genera and 71 families) from Europe, Cyprus, and Madeira. Macroclimatic gradients from boreal, via temperate to mediterranean are strongly related with a decreasing incidence of scalariform perforations, (almost) exclusively solitary vessels, and fibre-tracheids (i. e., fibres with distinctly bordered pits). In this sequence the incidence of different vessel size classes (vessel dimorphism) and vascular tracheids increases. Ring-porous tendencies and spiral vessei thickenings have their peaks in the temperate zone. The subtropical flora of Madeira shows low values for the percentage of species with any of the above attributes.
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Burton, Julia I., Eric K. Zenner et Lee E. Frelich. « Frost Crack Incidence in Northern Hardwood Forests of the Southern Boreal–North Temperate Transition Zone ». Northern Journal of Applied Forestry 25, no 3 (1 septembre 2008) : 133–38. http://dx.doi.org/10.1093/njaf/25.3.133.
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Abstract Frost cracks are common in northern hardwood stands near their northern range limits. Although they have long been attributed to the regional climate, temperature fluctuations result in surface cracks largely when internal wounds are present. We examined the relationship between the proportion of trees with frost cracks and both tree-level diameter class and stand structural characteristics in primary stands with a history of minimal logging (n = 4) and 67- to 97-year-old second-growth stands subjected to past heavy partial cuts and high grading (n = 8). We hypothesized that frost crack incidence would (1) be greater in the second-growth stands and (2) be associated with differences in structural attributes between the two stand types. High levels of frost cracking in primary stands indicated that cracks are not completely avoidable. However, the proportion of trees with frost cracks was significantly higher in second-growth than primary stands, particularly on small-diameter trees. For example, the odds for frost cracking were 1.66–3.74 times greater in second-growth than in primary stands in the 15-cm diameter class, but were not different in the 45+-cm diameter class. Frost cracking was positively associated with increasing diameter in both stand types. Structural characteristics reflecting tree size, stand basal area, and basal area of hardwoods were positively associated with the proportion of trees with frost cracks in second-growth stands but not in primary stands. Although the basal area of conifers was negatively associated with frost cracking, the effect was likely due to a reduction in hardwood basal area in the vicinity of conifers. We suggest that greater frost crack incidence in second-growth stands is likely a consequence of injuries to residual trees during selective logging.
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Gauci, Vincent, Sunitha Rao Pangala, Alexander Shenkin, Josep Barba, David Bastviken, Viviane Figueiredo, Carla Gomez et al. « Global atmospheric methane uptake by upland tree woody surfaces ». Nature 631, no 8022 (24 juillet 2024) : 796–800. http://dx.doi.org/10.1038/s41586-024-07592-w.
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AbstractMethane is an important greenhouse gas1, but the role of trees in the methane budget remains uncertain2. Although it has been shown that wetland and some upland trees can emit soil-derived methane at the stem base3,4, it has also been suggested that upland trees can serve as a net sink for atmospheric methane5,6. Here we examine in situ woody surface methane exchange of upland tropical, temperate and boreal forest trees. We find that methane uptake on woody surfaces, in particular at and above about 2 m above the forest floor, can dominate the net ecosystem contribution of trees, resulting in a net tree methane sink. Stable carbon isotope measurement of methane in woody surface chamber air and process-level investigations on extracted wood cores are consistent with methanotrophy, suggesting a microbially mediated drawdown of methane on and in tree woody surfaces and tissues. By applying terrestrial laser scanning-derived allometry to quantify global forest tree woody surface area, a preliminary first estimate suggests that trees may contribute 24.6–49.9 Tg of atmospheric methane uptake globally. Our findings indicate that the climate benefits of tropical and temperate forest protection and reforestation may be greater than previously assumed.
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Loehle, C. « Predicting Pleistocene climate from vegetation ». Climate of the Past Discussions 2, no 5 (23 octobre 2006) : 979–1000. http://dx.doi.org/10.5194/cpd-2-979-2006.
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Abstract. Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder than those produced by climate simulations. Biogeographic evidence also argues against these inferred cold climates. The recolonization of glaciated zones in eastern North America following the last ice age produced distinct biogeographic patterns. It has been assumed that a wide zone south of the ice was tundra or boreal parkland (Boreal-Parkland Zone or BPZ), which would have been recolonized from southern refugia as the ice melted, but the patterns in this zone differ from those in the glaciated zone, which creates a major biogeographic anomaly. In the glacial zone, there are few endemics but in the BPZ there are many across multiple taxa. In the glacial zone, there are the expected gradients of genetic diversity with distance from the ice-free zone, but no evidence of this is found in the BPZ. Many races and related species exist in the BPZ which would have merged or hybridized if confined to the same refugia. Evidence for distinct southern refugia for most temperate species is lacking. Extinctions of temperate flora were rare. The interpretation of spruce as a boreal climate indicator may be mistaken over much of the region if the spruce was actually an extinct temperate species. All of these anomalies call into question the concept that climates in the zone south of the ice were very cold or that temperate species had to migrate far to the south. Similar anomalies exist in Europe and on tropical mountains. An alternate hypothesis is that low CO2 levels gave an advantage to pine and spruce, which are the dominant trees in the BPZ, and to herbaceous species over trees, which also fits the observed pattern. Most temperate species could have survived across their current ranges at lower abundance by retreating to moist microsites. These would be microrefugia not easily detected by pollen records, especially if most species became rare. These results mean that climate reconstruction based on terrestrial plant indicators will not be valid for periods with markedly different CO2 levels.
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Zohner, Constantin M., Lidong Mo, Thomas A. M. Pugh, Jean‐Francois Bastin et Thomas W. Crowther. « Interactive climate factors restrict future increases in spring productivity of temperate and boreal trees ». Global Change Biology 26, no 7 (29 avril 2020) : 4042–55. http://dx.doi.org/10.1111/gcb.15098.
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Nilsson, Sven G., Mats Niklasson, Jonas Hedin, Gillis Aronsson, Jerzy M. Gutowski, Per Linder, Håkan Ljungberg, Grzegorz Mikusiński et Thomas Ranius. « Densities of large living and dead trees in old-growth temperate and boreal forests ». Forest Ecology and Management 161, no 1-3 (mai 2002) : 189–204. http://dx.doi.org/10.1016/s0378-1127(01)00480-7.
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Linkosalo, T., R. Hakkinen et H. Hanninen. « Models of the spring phenology of boreal and temperate trees : is there something missing ? » Tree Physiology 26, no 9 (1 septembre 2006) : 1165–72. http://dx.doi.org/10.1093/treephys/26.9.1165.
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Loehle, C. « Predicting Pleistocene climate from vegetation in North America ». Climate of the Past 3, no 1 (12 février 2007) : 109–18. http://dx.doi.org/10.5194/cp-3-109-2007.
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Abstract. Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder for eastern North America than those produced by climate simulations. It has been suggested that low CO2 levels could account for this discrepancy. In this study biogeographic evidence is used to test the CO2 effect model. The recolonization of glaciated zones in eastern North America following the last ice age produced distinct biogeographic patterns. It has been assumed that a wide zone south of the ice was tundra or boreal parkland (Boreal-Parkland Zone or BPZ), which would have been recolonized from southern refugia as the ice melted, but the patterns in this zone differ from those in the glaciated zone, which creates a major biogeographic anomaly. In the glacial zone, there are few endemics but in the BPZ there are many across multiple taxa. In the glacial zone, there are the expected gradients of genetic diversity with distance from the ice-free zone, but no evidence of this is found in the BPZ. Many races and related species exist in the BPZ which would have merged or hybridized if confined to the same refugia. Evidence for distinct southern refugia for most temperate species is lacking. Extinctions of temperate flora were rare. The interpretation of spruce as a boreal climate indicator may be mistaken over much of the region if the spruce was actually an extinct temperate species. All of these anomalies call into question the concept that climates in the zone south of the ice were extremely cold or that temperate species had to migrate far to the south. An alternate hypothesis is that low CO2 levels gave an advantage to pine and spruce, which are the dominant trees in the BPZ, and to herbaceous species over trees, which also fits the observed pattern. Thus climate reconstruction from pollen data is probably biased and needs to incorporate CO2 effects. Most temperate species could have survived across their current ranges at lower abundance by retreating to moist microsites. These would be microrefugia not easily detected by pollen records, especially if most species became rare. These results mean that climate reconstructions based on terrestrial plant indicators will not be valid for periods with markedly different CO2 levels.
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Watanabe, Sadamoto, et Satohiko Sasaki. « The Silvicultural Management System in temperate and boreal forests : A case history of the Hokkaido Tokyo University Forest ». Canadian Journal of Forest Research 24, no 6 (1 juin 1994) : 1176–85. http://dx.doi.org/10.1139/x94-155.
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Forest managers need new approaches for maintaining high stand volumes while keeping forests continuously productive and economically profitable. The Silvicultural Management System (SMS) accomplishes these objectives by increasing large-sized trees for periodic harvest, and continuously maintaining stand volumes at their highest possible levels. This system takes advantage of the diversity in growth, vigor, and longevity of dominant trees from a wide range of tree species found in natural forest ecosystems. Under the SMS developed at the Tokyo University Forest in Hokkaido, 13–17% of the stand volume is harvested at a cutting cycle of 8–10 years by removing the oldest mature trees. Residual stand volumes are maintained at about 70–80% of the levels found in natural old-growth stands. This removal of the oldest trees keeps the stands in a continuously healthy and productive state. The cutting level is planned to ensure a sufficient harvest to cover the construction costs of a necessary high-density forest road network that provides the great logging efficiency and limited maximum yarding distances. This form of selection cutting has proven to be highly productive, surpassing even the production realized under clear cutting. Well-managed cuttings under SMS improve the quality and quantity of the timber resource, with particular emphasis upon premium-quality hardwoods. Guidelines are given for individual tree selection cutting to produce premium-quality hardwoods, and based upon a high-density forest road network. The value of this high-quality timber makes such low-volume logging operations profitable. The SMS also maintains a favorable forest ecosystem for diverse wildlife and flora, and several endangered or threatened wildlife species that depend upon less dense mature forests occur in SMS forests. Managed forests with high-volume stocking also serve as an effective carbon dioxide sink.
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Lin, Jianhong, Daniel Berveiller, Christophe François, Heikki Hänninen, Alexandre Morfin, Gaëlle Vincent, Rui Zhang, Cyrille Rathgeber et Nicolas Delpierre. « A model of the within-population variability of budburst in forest trees ». Geoscientific Model Development 17, no 2 (31 janvier 2024) : 865–79. http://dx.doi.org/10.5194/gmd-17-865-2024.
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Abstract. Spring phenology is a key indicator of temperate and boreal ecosystems' response to climate change. To date, most phenological studies have analyzed the mean date of budburst in tree populations while overlooking the large variability of budburst among individual trees. The consequences of neglecting the within-population variability (WPV) of budburst when projecting the dynamics of tree communities are unknown. Here, we develop the first model designed to simulate the WPV of budburst in tree populations. We calibrated and evaluated the model on 48 442 budburst observations collected between 2000 and 2022 in three major temperate deciduous trees, namely, hornbeam (Carpinus betulus), oak (Quercus petraea) and chestnut (Castanea sativa). The WPV model received support for all three species, with a root mean square error of 5.7 ± 0.5 d for the prediction of unknown data. Retrospective simulations over 1961–2022 indicated earlier budburst as a consequence of ongoing climate warming. However, simulations revealed no significant change for the duration of budburst (DurBB, i.e., the time interval from BP20 to BP80 (with BP representing budburst percent), which respectively represent the date when 20 % and 80 % of trees in a population have reached budburst), due to a lack of significant temperature increase during DurBB in the past. This work can serve as a basis for the development of models targeting intra-population variability of other functional traits, which is of increasing interest in the context of climate change.
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Zohner, Constantin M., Lidong Mo, Susanne S. Renner, Jens-Christian Svenning, Yann Vitasse, Blas M. Benito, Alejandro Ordonez et al. « Late-spring frost risk between 1959 and 2017 decreased in North America but increased in Europe and Asia ». Proceedings of the National Academy of Sciences 117, no 22 (11 mai 2020) : 12192–200. http://dx.doi.org/10.1073/pnas.1920816117.
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Late-spring frosts (LSFs) affect the performance of plants and animals across the world’s temperate and boreal zones, but despite their ecological and economic impact on agriculture and forestry, the geographic distribution and evolutionary impact of these frost events are poorly understood. Here, we analyze LSFs between 1959 and 2017 and the resistance strategies of Northern Hemisphere woody species to infer trees’ adaptations for minimizing frost damage to their leaves and to forecast forest vulnerability under the ongoing changes in frost frequencies. Trait values on leaf-out and leaf-freezing resistance come from up to 1,500 temperate and boreal woody species cultivated in common gardens. We find that areas in which LSFs are common, such as eastern North America, harbor tree species with cautious (late-leafing) leaf-out strategies. Areas in which LSFs used to be unlikely, such as broad-leaved forests and shrublands in Europe and Asia, instead harbor opportunistic tree species (quickly reacting to warming air temperatures). LSFs in the latter regions are currently increasing, and given species’ innate resistance strategies, we estimate that ∼35% of the European and ∼26% of the Asian temperate forest area, but only ∼10% of the North American, will experience increasing late-frost damage in the future. Our findings reveal region-specific changes in the spring-frost risk that can inform decision-making in land management, forestry, agriculture, and insurance policy.
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Morin, Xavier, et Isabelle Chuine. « Will tree species experience increased frost damage due to climate change because of changes in leaf phenology ? » Canadian Journal of Forest Research 44, no 12 (décembre 2014) : 1555–65. http://dx.doi.org/10.1139/cjfr-2014-0282.
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In temperate zones, trees tend to unfold their leaves earlier due to climate warming. However, changes in the timing of the bud development also affect the dynamics of the cold-hardening process, which may increase frost injuries endured by trees because new leaves unfold at a period when frost events can still occur. This possible increase in frost damage in response to climate change is known as the “frost-damage hypothesis”. In this study, we have tested this hypothesis by forcing a process-based frost-injury model with process-based phenological models for 22 North American species with two Intergovernmental Panel on Climate Change storylines. Using a simplified parameterization of the frost-injury model, we found that risk of frost injury changed with climate change for all species. In fact, frost injury decreased for the vast majority of the species, but this trend varied across species and throughout each species’ distribution. We further explored the variability of response among species using their phenological and geographic characteristics. The interspecific trends depicted here show what could be the implications of climate change on the ecophysiology of boreal and temperate trees and highlight the importance of process-based models in studying the complexity of long-term impacts of climate change on species biology.
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Martinez, Jean-Jacques Itzhak, Reut Raz et Nyembezi Mgocheki. « Differential spatial distribution of arthropods under epiphytic lichens on trees ». Journal of Insect Biodiversity 2, no 15 (1 août 2014) : 1. http://dx.doi.org/10.12976/jib/2014.2.15.
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Epiphytic lichen thalli on trees may protect arthropods - herbivores or their natural enemies. Although the relationships between lichens on the forest floor to arthropods have been widely studied in boreal regions, those between epiphytic lichens and the arboreal arthropod fauna in temperate and Mediterranean climates are poorly investigated. In particular it is unknown if the animals use lichens differently located on different part of the trees. Our results indicate that numerous arthropods, herbivores and predators, may live in epiphytic lichen cover, and that more of them are found on the trunk than on old or young branches: an average of 2000 individuals were found under each meter square of the thallus covering the trunk of 20 trees, but fewer on branches. In particular more insects from more Orders were detected on trunks than on branches. We propose that this issue should be investigated further to clarify the exact status of epiphytic lichens in arthropod biodiversity conservation.
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Fedrowitz, Katja, et Lena Gustafsson. « Does the amount of trees retained at clearfelling of temperate and boreal forests influence biodiversity response ? » Environmental Evidence 1, no 1 (2012) : 5. http://dx.doi.org/10.1186/2047-2382-1-5.
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Nilsson, Sven G., Mats Niklasson, Jonas Hedin, Gillis Aronsson, Jerzy M. Gutowski, Per Linder, Håkan Ljungberg, Grzegorz Mikusiński et Thomas Ranius. « Erratum to “Densities of large living and dead trees in old-growth temperate and boreal forests” ». Forest Ecology and Management 178, no 3 (juin 2003) : 355–70. http://dx.doi.org/10.1016/s0378-1127(03)00084-7.
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Riedel, Jon L., Alice Telka, Andy Bunn et John J. Clague. « Reconstruction of climate and ecology of Skagit Valley, Washington, from 27.7 to 19.8 ka based on plant and beetle macrofossils ». Quaternary Research 106 (27 octobre 2021) : 94–112. http://dx.doi.org/10.1017/qua.2021.50.
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AbstractGlacial lake sediments exposed at two sites in Skagit Valley, Washington, encase abundant macrofossils dating from 27.7 to 19.8 cal ka BP. At the last glacial maximum (LGM) most of the valley floor was part of a regionally extensive arid boreal (subalpine) forest that periodically included montane and temperate trees and open boreal species such as dwarf birch, northern spikemoss, and heath. We used the modern distribution and climate of 14 species in 12 macrofossil assemblages and a probability density function approach to reconstruct the LGM climate. Median annual precipitation (MAP) at glacial Lake Concrete (GLC) was ~50% lower than today. In comparison, MAP at glacial Lake Skymo (GLS) was only ~10% lower, which eliminated the steep climate gradient observed today. Median January air temperature at GLC was up to 10.8°C lower than today at 23.5 cal ka BP and 8.7°C lower at GLS at 25.1 cal ka BP. Median July air temperature declines were smaller at GLC (3.4°C–5.0°C) and GLS (4.2°C–6.3°C). Warmer winters (+2°C to +4°C) and increases in MAP (+200 mm) occurred at 27.7, 25.9, 24.4, and 21.2–20.7 cal ka BP. These changes accord with other regional proxies and Dansgaard–Oeschger interstades in the North Atlantic.
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Fréchette, Bianca, et Anne de Vernal. « Evidence for large-amplitude biome and climate changes in Atlantic Canada during the last interglacial and mid-Wisconsinan periods ». Quaternary Research 79, no 2 (mars 2013) : 242–55. http://dx.doi.org/10.1016/j.yqres.2012.11.011.
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AbstractLast interglacial and mid Wisconsinan pollen data from sedimentary sequences of Cape Breton Island in Atlantic Canada were analyzed to reconstruct biome and climate conditions. Our results show warm and humid climate with mean annual temperature 6–7°C higher than today, up to 15–20% more sunshine and significantly longer growing season that fostered growth of temperate trees during the optimum of the last interglacial. The northern limit of the deciduous forest biome was then about 500 km north of its modern limit. Towards the end of the interglacial the deciduous forest was replaced by conifer/hardwood forest and boreal forest. Climate was then similar to modern. The transition from interglacial to glacial was marked by a change towards coniferous forest related to colder and dryer conditions. During the mid Wisconsinan, the development of forest tundra to boreal forest reflects migration of the Arctic Front and significant cooling with mean annual temperature anomalies of − 8 to − 12°C. The overall time series reflect large amplitude climate changes that point to high sensitivity of the southeastern Canadian margins, likely as a response to latitudinal shifts of the Gulf Stream and variable strength of the Labrador Current together with changes in large-scale atmospheric circulation pattern.
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Camm, E. L., D. C. Goetze, S. N. Silim et D. P. Lavender. « Cold storage of conifer seedlings : An update from the British Columbia perspective ». Forestry Chronicle 70, no 3 (1 juin 1994) : 311–16. http://dx.doi.org/10.5558/tfc70311-3.
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In both the temperate and boreal regions of North America and Scandinavia, conifer seedlings are routinely cold stored for several months in order to accommodate the schedules of nurseries and tree planters alike. It is critical to the success of the practice to understand the biology of the seedlings, in particular the influence of environmental factors such as temperature and light on their yearly cycle. Since Hocking and Nyland's important 1971 review, research has characterized the effects of different methodoligical parameters of the cold storage process (lift date, storage temperature, moisture, etc.) on a number of physiological aspects of the trees (root growth potential, photosynthesis, stress resistance). This has led to better guidelines and awareness on the manipulation of seedlings for cold storage. This article will review some of that research, concentrating on the Western experience. Key words: conifer seedlings, nurseries, cold storage, physiology, stress resistance
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Babst, Flurin, Olivier Bouriaud, Benjamin Poulter, Valerie Trouet, Martin P. Girardin et David C. Frank. « Twentieth century redistribution in climatic drivers of global tree growth ». Science Advances 5, no 1 (janvier 2019) : eaat4313. http://dx.doi.org/10.1126/sciadv.aat4313.
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Energy and water limitations of tree growth remain insufficiently understood at large spatiotemporal scales, hindering model representation of interannual or longer-term ecosystem processes. By assessing and statistically scaling the climatic drivers from 2710 tree-ring sites, we identified the boreal and temperate land areas where tree growth during 1930–1960 CE responded positively to temperature (20.8 ± 3.7 Mio km2; 25.9 ± 4.6%), precipitation (77.5 ± 3.3 Mio km2; 96.4 ± 4.1%), and other parameters. The spatial manifestation of this climate response is determined by latitudinal and altitudinal temperature gradients, indicating that warming leads to geographic shifts in growth limitations. We observed a significant (P< 0.001) decrease in temperature response at cold-dry sites between 1930–1960 and 1960–1990 CE, and the total temperature-limited area shrunk by −8.7 ± 0.6 Mio km2. Simultaneously, trees became more limited by atmospheric water demand almost worldwide. These changes occurred under mild warming, and we expect that continued climate change will trigger a major redistribution in growth responses to climate.
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Richard, Pierre JH, Serge Occhietti, Martine Clet et Alayn C. Larouche. « Paléophytogéographie de la formation de Scarborough : nouvelles données et implications ». Canadian Journal of Earth Sciences 36, no 10 (1 octobre 1999) : 1589–602. http://dx.doi.org/10.1139/e99-066.
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Palynological study of the upper part of the Don Formation, in the Toronto area, confirms the progressive change from a mixed forest with numerous thermophilous trees (Quercus, Ulmus, Carya) to a cold balsam fir forest (Abies balsamea, Picea mariana, Pinus banksiana) towards the end of the Sangamonian climatic optimum. The Scarborough Formation pollen content indicates a forest-tundra or treed tundra environment similar to modern subarctic conditions. Macrofossil content also points to harsh climatic conditions. Mean annual temperature could then have been 10°C lower than the present in the Toronto area. Our data refute the reconstruction of a climatic cycle (cold-warmer-cold) within the Scarborough Formation. To explain the simultaneous presence of floristic elements typical of presently contrasted climatic regions (cold boreal, warm temperate), we propose that Lake Scarborough acted as a climatic buffer for riverine plants: thermophilous species survived in an englaciation context in remote regions. The upper part of the Don Formation corresponds with the end of the Sangamonian climatic optimum (end of isotopic substage 5e). After a sedimentary gap of unknown duration, the Scarborough Formation is apparently correlative to the Lévrard Till in the Middle St. Lawrence River Valley (isotopic stage 5b).
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Aikio, Sami, Kari Taulavuori, Sonja Hurskainen, Erja Taulavuori et Juha Tuomi. « Contributions of day length, temperature and individual variability on the rate and timing of leaf senescence in the common lilac Syringa vulgaris ». Tree Physiology 39, no 6 (29 avril 2019) : 961–70. http://dx.doi.org/10.1093/treephys/tpz013.
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Abstract Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.
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Garighan, Julio, Etienne Dvorak, Joan Estevan, Karine Loridon, Bruno Huettel, Gautier Sarah, Isabelle Farrera et al. « The Identification of Small RNAs Differentially Expressed in Apple Buds Reveals a Potential Role of the Mir159-MYB Regulatory Module during Dormancy ». Plants 10, no 12 (3 décembre 2021) : 2665. http://dx.doi.org/10.3390/plants10122665.
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Winter dormancy is an adaptative mechanism that temperate and boreal trees have developed to protect their meristems against low temperatures. In apple trees (Malus domestica), cold temperatures induce bud dormancy at the end of summer/beginning of the fall. Apple buds stay dormant during winter until they are exposed to a period of cold, after which they can resume growth (budbreak) and initiate flowering in response to warmer temperatures in spring. It is well-known that small RNAs modulate temperature responses in many plant species, but however, how small RNAs are involved in genetic networks of temperature-mediated dormancy control in fruit tree species remains unclear. Here, we have made use of a recently developed ARGONAUTE (AGO)-purification technique to isolate small RNAs from apple buds. A small RNA-seq experiment resulted in the identification of 17 micro RNAs (miRNAs) that change their pattern of expression in apple buds during dormancy. Furthermore, the functional analysis of their predicted target genes suggests a main role of the 17 miRNAs in phenylpropanoid biosynthesis, gene regulation, plant development and growth, and response to stimulus. Finally, we studied the conservation of the Arabidopsis thaliana regulatory miR159-MYB module in apple in the context of the plant hormone abscisic acid homeostasis.
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Quinzin, Maud C., Signe Normand, Simon Dellicour, Jens-Christian Svenning et Patrick Mardulyn. « Glacial survival of trophically linked boreal species in northern Europe ». Proceedings of the Royal Society B : Biological Sciences 284, no 1856 (7 juin 2017) : 20162799. http://dx.doi.org/10.1098/rspb.2016.2799.
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Whether non-arctic species persisted in northern Europe during the Last Glacial Maximum (LGM) is highly debated. Until now, the debate has mostly focused on plants, with little consideration for other groups of organisms, e.g. the numerous plant-dependent insect species. Here, we study the late-Quaternary evolution of the European range of a boreo-montane leaf beetle, Gonioctena intermedia , which feeds exclusively on the boreal and temperate trees Prunus padus and Sorbus aucuparia . Using species distribution models, we estimated the congruence between areas of past and present suitable climate for this beetle and its host plants. Then we derived historical hypotheses from the congruent range estimates, and evaluated their compatibility with observed DNA sequence variation at five independent loci. We investigated compatibility using computer simulations of population evolution under various coalescence models. We find strong evidence for range modifications in response to late-Quaternary climate changes, and support for the presence of populations of G. intermedia in northern Europe since the beginning of the last glaciation. The presence of a co-dependent insect in the region through the LGM provides new evidence supporting the glacial survival of cold-tolerant tree species in northern Europe.
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Strong, Wayne L. « Divergent Growth and Changing Climate Relationships of Boreal and Subalpine Spruce in Southern Yukon, Canada ». ARCTIC 74, no 4 (18 janvier 2022) : 456–68. http://dx.doi.org/10.14430/arctic74289.
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Tree-ring data for 1942 – 2013 were used to determine if boreal and subalpine Picea albertiana S. Brown emend. Strong & Hills radial growth rates changed after 1950 in southern Yukon, northwest Canada. The latter year represented the beginning of accelerated atmospheric greenhouse gas accumulation, which has subsequently caused global climate changes. Ring-width chronologies for both boreal and subalpine trees were constructed using 80 trees. Individual ring-width sequences were crossdated, age-detrended, and converted to tree ring-width indices (RWI). In 2013, boreal and subalpine RWI were 41% and 169% greater than in 1950, respectively. In contrast, elevational treeline chronologies in the region typically decreased 20% – 70%. During 1942 – 2013, boreal and subalpine chronologies were significantly, at best modestly (r < |0.36|), and exclusively correlated with either moisture or temperature variables, respectively. Within this same time frame, RWI-climate variable correlates differed between the early and late phases of each chronology. Average pre-1969 or early-phase boreal correlations based on a 19-year moving window reached a maximum of – 0.56. Late-phase chronology correlations typically shifted towards weaker associations with climate variables (typically +0.04 to +0.30). For boreal RWI, 25 of 68 tested climate variables shifted as much as 0.40 – 0.88 correlation coefficient units between the early and late phases of the chronologies. Subalpine RWI were correlated only with July – August precipitation during the early phase of its chronology. These changes suggest responses by spruce to climate have shifted since 1970. The modest 1942 – 2013 RWI-climate variable correlations likely reflect the result of these changing ecological relationships.
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Leithead, Mark D., Madhur Anand et Lucas C. R. Silva. « Northward migrating trees establish in treefall gaps at the northern limit of the temperate–boreal ecotone, Ontario, Canada ». Oecologia 164, no 4 (22 septembre 2010) : 1095–106. http://dx.doi.org/10.1007/s00442-010-1769-z.
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Maurya, Jay P., Pal C. Miskolczi, Sanatkumar Mishra, Rajesh Kumar Singh et Rishikesh P. Bhalerao. « A genetic framework for regulation and seasonal adaptation of shoot architecture in hybrid aspen ». Proceedings of the National Academy of Sciences 117, no 21 (11 mai 2020) : 11523–30. http://dx.doi.org/10.1073/pnas.2004705117.
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Shoot architecture is critical for optimizing plant adaptation and productivity. In contrast with annuals, branching in perennials native to temperate and boreal regions must be coordinated with seasonal growth cycles. How branching is coordinated with seasonal growth is poorly understood. We identified key components of the genetic network that controls branching and its regulation by seasonal cues in the model tree hybrid aspen. Our results demonstrate that branching and its control by seasonal cues is mediated by mutually antagonistic action of aspen orthologs of the flowering regulatorsTERMINAL FLOWER 1(TFL1) andAPETALA1(LIKE APETALA 1/LAP1).LAP1promotes branching through local action in axillary buds.LAP1acts in a cytokinin-dependent manner, stimulating expression of the cell-cycle regulatorAIL1and suppressingBRANCHED1expression to promote branching. Short photoperiod and low temperature, the major seasonal cues heralding winter, suppress branching by simultaneous activation ofTFL1and repression of theLAP1pathway. Our results thus reveal the genetic network mediating control of branching and its regulation by environmental cues facilitating integration of branching with seasonal growth control in perennial trees.
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Howe, Glenn T., Sally N. Aitken, David B. Neale, Kathleen D. Jermstad, Nicholas C. Wheeler et Tony HH Chen. « From genotype to phenotype : unraveling the complexities of cold adaptation in forest trees ». Canadian Journal of Botany 81, no 12 (1 décembre 2003) : 1247–66. http://dx.doi.org/10.1139/b03-141.
Texte intégralRésumé :
Adaptation to winter cold in temperate and boreal trees involves complex genetic, physiological, and developmental processes. Genecological studies demonstrate the existence of steep genetic clines for cold adaptation traits in relation to environmental (mostly temperature related) gradients. Population differentiation is generally stronger for cold adaptation traits than for other quantitative traits and allozymes. Therefore, these traits appear to be under strong natural selection. Nonetheless, high levels of genetic variation persist within populations. The genetic control of cold adaptation traits ranges from weak to strong, with phenological traits having the highest heritabilities. Within-population genetic correlations among traits range from negligible to moderate. Generally, bud phenology and cold hardiness in the fall are genetically uncorrelated with bud phenology and cold hardiness in the spring. Analyses of quantitative trait loci indicate that cold adaptation traits are mostly controlled by multiple genes with small effects and that quantitative trait loci × environment interactions are common. Given this inherent complexity, we suggest that future research should focus on identifying and developing markers for cold adaptation candidate genes, then using multilocus, multi allelic analytical techniques to uncover the relationships between genotype and phenotype at both the individual and population levels. Ultimately, these methods may be useful for predicting the performance of genotypes in breeding programs and for better understanding the evolutionary ecology of forest trees.Key words: association genetics, cold hardiness, dormancy, genecology, bud phenology, quantitative trait loci.
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Mossop, Brent, et Michael J. Bradford. « Importance of large woody debris for juvenile chinook salmon habitat in small boreal forest streams in the upper Yukon River basin, Canada ». Canadian Journal of Forest Research 34, no 9 (1 septembre 2004) : 1955–66. http://dx.doi.org/10.1139/x04-066.
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The importance of large woody debris (LWD) in forested stream ecosystems is well documented. However, little is known about LWD in northern boreal forest streams. We investigated the abundance, characteristics, and function of LWD in 13 small tributary streams of the upper Yukon River basin, Yukon Territory, Canada. LWD abundance was similar to values reported from temperate regions, whereas LWD size and total volume were well below values for the Pacific Northwest. LWD formed 28% of the pools, which provide important habitat for juvenile chinook salmon (Oncorhynchus tshawytscha Walbaum). The median diameter of pool-forming pieces was 17 cm, and ring counts on fallen riparian trees indicated that pool-forming pieces were likely 70200 years old when downed. Juvenile chinook salmon density was correlated with LWD abundance in our study reaches. We conclude that despite differences in climate and forest type, LWD in Yukon streams and LWD in temperate regions appear to perform a similar function in creating fish habitat. Resource managers should consider the relatively slow tree growth and thus potentially long recovery times following human disturbances in these watersheds.
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CHEBAKOVA, N. M., E. V. BAZHINA, E. I. PARFENOVA et V. A. SENASHOVA. « IN SEARCH OF AN X FACTOR : A REVIEW OF PUBLICATIONS ON THE ISSUE OF DARK-NEEDLED FOREST DECLINE/DIEBACK IN NORTHERN EURASIA ». Meteorologiya i Gidrologiya, no 5 (mai 2022) : 123–40. http://dx.doi.org/10.52002/0130-2906-2022-5-123-140.
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A critical review of contemporary publications searching for the causes of the decline/dieback of dark-needled forests in the boreal and temperate zones over Northern Eurasia with an emphasis on the southern Siberian mountains is presented. Three groups of factors were considered: primary abiotic factors that weaken the tree defense mechanism (climate aridization, total ozone column, ultraviolet radiation (UV-B), dimming), anthropogenic factors (air pollution), and secondary biotic factors (invasive insect pests and phytopatogens that inhabit weakened trees, which finally leads to their decline/dieback). As there is no irrefutable evidence of the fatal impact of one particular factor, a synergic effect of some of them is possible against a certain climatic background. Further investigations are necessary to find out causes for the dark-needled forest decline/dieback in Northern Eurasia.
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Carpenter, Joshua, Jinha Jung, Sungchan Oh, Brady Hardiman et Songlin Fei. « An Unsupervised Canopy-to-Root Pathing (UCRP) Tree Segmentation Algorithm for Automatic Forest Mapping ». Remote Sensing 14, no 17 (30 août 2022) : 4274. http://dx.doi.org/10.3390/rs14174274.
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Terrestrial laser scanners, unmanned aerial LiDAR, and unmanned aerial photogrammetry are increasingly becoming the go-to methods for forest analysis and mapping. The three-dimensionality of the point clouds generated by these technologies is ideal for capturing the structural features of trees such as trunk diameter, canopy volume, and biomass. A prerequisite for extracting these features from point clouds is tree segmentation. This paper introduces an unsupervised method for segmenting individual trees from point clouds. Our novel, canopy-to-root, least-cost routing method segments trees in a single routine, accomplishing stem location and tree segmentation simultaneously without needing prior knowledge of tree stem locations. Testing on benchmark terrestrial-laser-scanned datasets shows that we achieve state-of-the-art performances in individual tree segmentation and stem-mapping accuracy on boreal and temperate hardwood forests regardless of forest complexity. To support mapping at scale, we test on unmanned aerial photogrammetric and LiDAR point clouds and achieve similar results. The proposed algorithm’s independence from a specific data modality, along with its robust performance in simple and complex forest environments and accurate segmentation results, make it a promising step towards achieving reliable stem-mapping capabilities and, ultimately, towards building automatic forest inventory procedures.
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Montgomery, Rebecca A., Karen E. Rice, Artur Stefanski, Roy L. Rich et Peter B. Reich. « Phenological responses of temperate and boreal trees to warming depend on ambient spring temperatures, leaf habit, and geographic range ». Proceedings of the National Academy of Sciences 117, no 19 (27 avril 2020) : 10397–405. http://dx.doi.org/10.1073/pnas.1917508117.
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Changes in plant phenology associated with climate change have been observed globally. What is poorly known is whether and how phenological responses to climate warming will differ from year to year, season to season, habitat to habitat, or species to species. Here, we present 5 y of phenological responses to experimental warming for 10 subboreal tree species. Research took place in the open-air B4WarmED experiment in Minnesota. The design is a two habitat (understory and open) × three warming treatments (ambient, +1.7 °C, +3.4 °C) factorial at two sites. Phenology was measured twice weekly during the growing seasons of 2009 through 2013. We found significant interannual variation in the effect of warming and differences among species in response to warming that relate to geographic origin and plant functional group. Moreover, responses to experimental temperature variation were similar to responses to natural temperature variation. Warming advanced the date of budburst more in early compared to late springs, suggesting that to simulate interannual variability in climate sensitivity of phenology, models should employ process-based or continuous development approaches. Differences among species in timing of budburst were also greater in early compared to late springs. Our results suggest that climate change—which will make most springs relatively “early”—could lead to a future with more variable phenology among years and among species, with consequences including greater risk of inappropriately early leafing and altered interactions among species.
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Griffin, Kevin L., et Case M. Prager. « Where does the carbon go ? Thermal acclimation of respiration and increased photosynthesis in trees at the temperate-boreal ecotone ». Tree Physiology 37, no 3 (15 février 2017) : 281–84. http://dx.doi.org/10.1093/treephys/tpw133.
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Drouin, Mélanie, Robert Bradley, Line Lapointe et Joann Whalen. « Non-native anecic earthworms (Lumbricus terrestris L.) reduce seed germination and seedling survival of temperate and boreal trees species ». Applied Soil Ecology 75 (mars 2014) : 145–49. http://dx.doi.org/10.1016/j.apsoil.2013.11.006.
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Lupi, Carlo, Hubert Morin, Annie Deslauriers, Sergio Rossi et Daniel Houle. « Increasing nitrogen availability and soil temperature : effects on xylem phenology and anatomy of mature black spruce1This article is one of a selection of papers from the 7th International Conference on Disturbance Dynamics in Boreal Forests. » Canadian Journal of Forest Research 42, no 7 (juillet 2012) : 1277–88. http://dx.doi.org/10.1139/x2012-055.
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Since plant growth in the boreal forest is often considered to be limited by low temperatures and low N availability and these variables are projected to increase due to climate warming and increased anthropogenic activities, it is important to understand whether and to what extent these disturbances may affect the growth of boreal trees. In this study, the hypotheses that wood phenology and anatomy were affected by increased soil temperatures and N depositions have been tested in two mature black spruce ( Picea mariana (Mill.) BSP) stands at different altitudes in Quebec, Canada. For 3 years, soil temperature was increased by 4 °C during the first part of the growing season and precipitations containing three times the current N concentration were added in the field by frequent canopy applications. Soil warming resulted in earlier onsets of xylogenesis and interacted with N addition producing longer durations of xylogenesis for the treated trees. The effect of warming was especially marked in the phenology of roots, while wood production, in terms of number of tracheids, was not affected by the treatment. Xylem anatomy and soil and needle chemistry showed no effect of the treatments, except for an increase of cell wall thickness in earlywood of treated trees. This short-term experiment with black spruce suggested that previous fertilization studies that used large and unrealistic rates of N addition may have overestimated the impact of N depositions on boreal forest productivity.
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van Leeuwen, T. T., G. R. van der Werf, A. A. Hoffmann, R. G. Detmers, G. Rücker, N. H. F. French, S. Archibald et al. « Biomass burning fuel consumption rates : a field measurement database ». Biogeosciences Discussions 11, no 6 (5 juin 2014) : 8115–80. http://dx.doi.org/10.5194/bgd-11-8115-2014.
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Abstract. Landscape fires show large variability in the amount of biomass or fuel consumed per unit area burned. These fuel consumption (FC) rates depend on the biomass available to burn and the fraction of the biomass that is actually combusted, and can be combined with estimates of area burned to assess emissions. While burned area can be detected from space and estimates are becoming more reliable due to improved algorithms and sensors, FC rates are either modeled or taken selectively from the literature. We compiled the peer-reviewed literature on FC rates for various biomes and fuel categories to better understand FC rates and variability, and to provide a~database that can be used to constrain biogeochemical models with fire modules. We compiled in total 76 studies covering 10 biomes including savanna (15 studies, average FC of 4.6 t DM (dry matter) ha−1), tropical forest (n = 19, FC = 126), temperate forest (n = 11, FC = 93), boreal forest (n = 16, FC = 39), pasture (n = 6, FC = 28), crop residue (n = 4, FC = 6.5), chaparral (n = 2, FC = 32), tropical peatland (n = 4, FC = 314), boreal peatland (n = 2, FC = 42), and tundra (n = 1, FC = 40). Within biomes the regional variability in the number of measurements was sometimes large, with e.g. only 3 measurement locations in boreal Russia and 35 sites in North America. Substantial regional differences were found within the defined biomes: for example FC rates of temperate pine forests in the USA were 38% higher than Australian forests dominated by eucalypt trees. Besides showing the differences between biomes, FC estimates were also grouped into different fuel classes. Our results highlight the large variability in FC rates, not only between biomes but also within biomes and fuel classes. This implies that care should be taken with using averaged values, and our comparison with FC rates from GFED3 indicates that also modeling studies have difficulty in representing the dynamics governing FC.
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Danks, H. V., et R. G. Foottit. « INSECTS OF THE BOREAL ZONE OF CANADA ». Canadian Entomologist 121, no 8 (août 1989) : 625–90. http://dx.doi.org/10.4039/ent121625-8.
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AbstractThe boreal zone of Canada extends across the continent over millions of square kilometres. Characterizing the insects of this cool temperate zone is especially important for an understanding of the Canadian fauna in general, and for northern forestry. The boreal zone supports simple coniferous forests with some deciduous trees and an understory of a few common vascular plants, mosses, and lichens. This enormous area of apparently similar vegetation nevertheless shows very great spatial and temporal heterogeneity, with a wide range of subhabitats. Aquatic habitats of many different kinds are especially well represented in the zone. The diversity of terrestrial habitats is maintained chiefly by disturbance, especially fire and seasonal flooding, and contributes greatly to faunal diversity.About 22 000 insect species are estimated to occur in the zone, far fewer than in more southern zones. Northern taxa, notably Diptera, are relatively well represented. The distributions and patterns of variation of the species are summarized. About half have transcontinental ranges, and many occur also in forested habitats in the western mountains south of the boreal zone. About 8% of the species appear to be holarctic. Few species that occur in the boreal zone are strictly confined to it, however. Generalist species in fresh water and other widespread habitats are conspicuous. Many species are centred farther south, and extend northward into the zone to varying degrees.Adaptations to northern conditions have been reported in many boreal insects. For example, the short growing season is reflected by the prevalence of univoltine species. Insects survive the long cold winters by cold-hardiness and dormancies. Species from disturbed habitats disperse widely. The limited diversity of resources is confirmed by the fact that the food range of some groups of herbivores is wider than in their southern relatives.Boreal ecosystem relationships are complex, especially relative to the arctic. Numerous associations among insects, and between insects and other organisms, have been demonstrated. However, some evidence suggests that the structure of northern biotic communities might depend more on the tolerances of individual species than on interactions among the species.The population dynamics of boreal forest insects, notably the spruce budworm, are discussed. In view of the spatial and temporal complexity of the boreal zone, the diversity of interactions with abiotic and biotic factors, and the prevalence of data that correlate with rather than explain population changes, our current failure to understand “outbreaks” of certain boreal insects is not surprising, because many factors probably combine to determine the population of a given species at a given lime and place.Information on most aspects of the composition and biology of the boreal fauna is incomplete. Data on boreal species have been collected chiefly in southern transitional ecosystems adjacent to boreal zones, rather than in truly boreal systems. Basic taxonomic information on several important taxa, as well as detailed taxonomic and morphometric information about individual species, is especially scanty. However, substantial and coordinated studies of boreal faunas will yield information of great interest and value. Some approaches relevant to further work in taxonomic and ecological arenas are suggested.
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Bell, F. Wayne, Maureen Kershaw, Isabelle Aubin, Nelson Thiffault, Jennifer Dacosta et Alan Wiensczyk. « Ecology and Traits of Plant Species that Compete with Boreal and Temperate Forest Conifers : An Overview of Available Information and its Use in Forest Management in Canada ». Forestry Chronicle 87, no 02 (avril 2011) : 161–74. http://dx.doi.org/10.5558/tfc2011-006.
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In boreal and temperate forests in Canada, at least 71 plant species, including trees, shrubs, herbs, grasses, and ferns, have the potential to significantly reduce the growth of conifer regeneration. A thorough understanding of the autecology of these plants—their response to their environment—can help resource managers to improve their approaches to vegetation management, thereby maximizing crop tree growth and survival. In this paper, we highlight key sources of information about the autecology of the major species that compete with forest conifers, including books and field guides, journal series, Web sites, and plant trait databases. We suggest ways that this information can be applied in resource management, recommend approaches for maintaining and updating this information, and underline the needs for developing a single, consolidated, comprehensive source of such information for use by resource managers and researchers. Information gaps are also briefly discussed.
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Man, Rongzhou, et Pengxin Lu. « Effects of thermal model and base temperature on estimates of thermal time to bud break in white spruce seedlings ». Canadian Journal of Forest Research 40, no 9 (septembre 2010) : 1815–20. http://dx.doi.org/10.1139/x10-129.
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To improve the predictability of bud burst and growth of boreal trees under varying climate, the thermal time for bud break in white spruce ( Picea glauca (Moench) Voss) seedlings was evaluated under a range of temperature conditions in controlled environment chambers. Thermal time requirements were calculated as the sum of growing degree days or growing degree hours above base temperatures ranging from –1 to 5 °C. The results indicated that the common modeling approach, which uses a high base temperature of 5 °C and growing degree days, may not be appropriate for future climatic conditions. Estimates of thermal time requirements using a base temperature of 5 °C varied considerably among temperature treatments and thus would reduce the predictability of bud burst under changing climate. In contrast, estimates of thermal time requirements with lower temperatures closer to 1 °C were relatively consistent among treatments. Growing degree hour models were less sensitive to base temperature than degree day models. These results should help in the selection of appropriate base temperatures and thermal time models in quantification of thermal time for bud burst modeling in other boreal trees.
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Locosselli, Giuliano Maselli, Roel J. W. Brienen, Melina de Souza Leite, Manuel Gloor, Stefan Krottenthaler, Alexandre A. de Oliveira, Jonathan Barichivich et al. « Global tree-ring analysis reveals rapid decrease in tropical tree longevity with temperature ». Proceedings of the National Academy of Sciences 117, no 52 (14 décembre 2020) : 33358–64. http://dx.doi.org/10.1073/pnas.2003873117.
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Forests are the largest terrestrial biomass pool, with over half of this biomass stored in the highly productive tropical lowland forests. The future evolution of forest biomass depends critically on the response of tree longevity and growth rates to future climate. We present an analysis of the variation in tree longevity and growth rate using tree-ring data of 3,343 populations and 438 tree species and assess how climate controls growth and tree longevity across world biomes. Tropical trees grow, on average, two times faster compared to trees from temperate and boreal biomes and live significantly shorter, on average (186 ± 138 y compared to 322 ± 201 y outside the tropics). At the global scale, growth rates and longevity covary strongly with temperature. Within the warm tropical lowlands, where broadleaf species dominate the vegetation, we find consistent decreases in tree longevity with increasing aridity, as well as a pronounced reduction in longevity above mean annual temperatures of 25.4 °C. These independent effects of temperature and water availability on tree longevity in the tropics are consistent with theoretical predictions of increases in evaporative demands at the leaf level under a warmer and drier climate and could explain observed increases in tree mortality in tropical forests, including the Amazon, and shifts in forest composition in western Africa. Our results suggest that conditions supporting only lower tree longevity in the tropical lowlands are likely to expand under future drier and especially warmer climates.
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Coulombe, David, Luc Sirois et David Paré. « Effect of harvest gap formation and thinning on soil nitrogen cycling at the boreal–temperate interface ». Canadian Journal of Forest Research 47, no 3 (mars 2017) : 308–18. http://dx.doi.org/10.1139/cjfr-2016-0301.
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In mixedwood forest, different types of commercial thinning that generate different gap sizes are being tested as alternatives to clearcutting to create forest stands with an irregular structure that would emulate the pre-industrial forests. The main goal of this study was to investigate the soil nitrogen (N) dynamics in response to two partial harvesting treatments, used alone or in combination: commercial thinning creating tree-size canopy gaps and harvest gaps creating 0.05 ha gaps. In a 30 year old balsam fir (Abies balsamea (L.) Mill.) stand, both treatments, alone or in combination, as well as unharvested controls were compared on replicated 0.75 ha plots. The most noticeable changes following treatments were observed in gaps, while commercial thinning did not significantly influence any of the parameters assessed. In gaps, increases in N mineralization rates and mineral N concentrations and proportions (NO3−-N and NH4+-N) relative to dissolved organic N were observed. Our results suggest that these changes are caused by the increase in soil temperature and water content. In these forests, the response threshold of the N cycling regarding the size of the intervention would therefore be located between the removal of one or a few trees (one to three stems, 6–12 m2) and a gap of 500 m2. Other studies conducted in different climate and forest types have shown that this threshold could be of equivalent or of a smaller size. These findings will contribute to optimizing our management strategies regarding partial cuts or small-scale clearcuts.
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Rey, Fabian, Erika Gobet, Christoph Schwörer, Albert Hafner, Sönke Szidat et Willy Tinner. « Climate impacts on vegetation and fire dynamics since the last deglaciation at Moossee (Switzerland) ». Climate of the Past 16, no 4 (28 juillet 2020) : 1347–67. http://dx.doi.org/10.5194/cp-16-1347-2020.
Texte intégralRésumé :
Abstract. Since the Last Glacial Maximum (LGM; end ca. 19 000 cal BP) central European plant communities have been shaped by changing climatic and anthropogenic disturbances. Understanding long-term ecosystem reorganizations in response to past environmental changes is crucial to draw conclusions about the impact of future climate change. So far, it has been difficult to address the post-deglaciation timing and ecosystem dynamics due to a lack of well-dated and continuous sediment sequences covering the entire period after the LGM. Here, we present a new paleoecological study with exceptional chronological time control using pollen, spores and microscopic charcoal from Moossee (Swiss Plateau, 521 m a.s.l.) to reconstruct the vegetation and fire history over the last ca. 19 000 years. After lake formation in response to deglaciation, five major pollen-inferred ecosystem rearrangements occurred at ca. 18 800 cal BP (establishment of steppe tundra), 16 000 cal BP (spread of shrub tundra), 14 600 cal BP (expansion of boreal forests), 11 600 cal BP (establishment of the first temperate deciduous tree stands composed of, e.g., Quercus, Ulmus, Alnus) and 8200 cal BP (first occurrence of mesophilous Fagus sylvatica trees). These vegetation shifts were caused by climate changes at ca. 19 000, 16 000, 14 700, 11 700 and 8200 cal BP. Vegetation responses occurred with no apparent time lag to climate change when the mutual chronological uncertainties are considered. This finding is in agreement with further evidence from southern and central Europe and might be explained by the proximity to the refugia of boreal and temperate trees (<400 km) and rapid species spreads. Our palynological record sets the beginning of millennial-scale land use with periodically increased fire and agricultural activities of the Neolithic period at ca. 7000 cal BP. Subsequently, humans rather than climate triggered changes in vegetation composition and structure. We conclude that Fagus sylvatica forests were resilient to long-term anthropogenic and climatic impacts of the Mid and the Late Holocene. However, future climate warming and in particular declining moisture availability may cause unprecedented reorganizations of central European beech-dominated forest ecosystems.
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van Leeuwen, T. T., G. R. van der Werf, A. A. Hoffmann, R. G. Detmers, G. Rücker, N. H. F. French, S. Archibald et al. « Biomass burning fuel consumption rates : a field measurement database ». Biogeosciences 11, no 24 (19 décembre 2014) : 7305–29. http://dx.doi.org/10.5194/bg-11-7305-2014.
Texte intégralRésumé :
Abstract. Landscape fires show large variability in the amount of biomass or fuel consumed per unit area burned. Fuel consumption (FC) depends on the biomass available to burn and the fraction of the biomass that is actually combusted, and can be combined with estimates of area burned to assess emissions. While burned area can be detected from space and estimates are becoming more reliable due to improved algorithms and sensors, FC is usually modeled or taken selectively from the literature. We compiled the peer-reviewed literature on FC for various biomes and fuel categories to understand FC and its variability better, and to provide a database that can be used to constrain biogeochemical models with fire modules. We compiled in total 77 studies covering 11 biomes including savanna (15 studies, average FC of 4.6 t DM (dry matter) ha−1 with a standard deviation of 2.2), tropical forest (n = 19, FC = 126 ± 77), temperate forest (n = 12, FC = 58 ± 72), boreal forest (n = 16, FC = 35 ± 24), pasture (n = 4, FC = 28 ± 9.3), shifting cultivation (n = 2, FC = 23, with a range of 4.0–43), crop residue (n = 4, FC = 6.5 ± 9.0), chaparral (n = 3, FC = 27 ± 19), tropical peatland (n = 4, FC = 314 ± 196), boreal peatland (n = 2, FC = 42 [42–43]), and tundra (n = 1, FC = 40). Within biomes the regional variability in the number of measurements was sometimes large, with e.g. only three measurement locations in boreal Russia and 35 sites in North America. Substantial regional differences in FC were found within the defined biomes: for example, FC of temperate pine forests in the USA was 37% lower than Australian forests dominated by eucalypt trees. Besides showing the differences between biomes, FC estimates were also grouped into different fuel classes. Our results highlight the large variability in FC, not only between biomes but also within biomes and fuel classes. This implies that substantial uncertainties are associated with using biome-averaged values to represent FC for whole biomes. Comparing the compiled FC values with co-located Global Fire Emissions Database version 3 (GFED3) FC indicates that modeling studies that aim to represent variability in FC also within biomes, still require improvements as they have difficulty in representing the dynamics governing FC.
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Cienciala, Emil, Per-Erik Mellander, Jiří Kučera, Magda Oplutilová, Mikaell Ottosson-Löfvenius et Kevin Bishop. « The effect of a north-facing forest edge on tree water use in a boreal Scots pine stand ». Canadian Journal of Forest Research 32, no 4 (1 avril 2002) : 693–702. http://dx.doi.org/10.1139/x02-013.
Texte intégralRésumé :
Tree water use and growth increment were studied in a north-facing forest edge of a 70-year-old monospecific Scots pine (Pinus sylvestris L.) stand growing on poor sandy soils in the northern boreal zone of Sweden. The forest edge in this study bordered a 20-year-old clearcut. There were differences in water use and growth increment during the growing season between trees growing at the forest edge and trees growing in the forest interior. These differences were likely related to soil conditions, such as access to soil moisture, soil temperature, and soil frost conditions, whereas an effect of aboveground microclimate was not found. The estimated tree water use and growth increment over one growing season tended to be greater for trees at the edge zone relative to those from the interior. The variability of the measured tree water fluxes was high, especially for the edge-zone trees. There were also structural differences between the two groups of trees, most notably in the radial profile of conductive xylem, in tree height, and in green crown length, but these differences were on the limits of statistical significance. The estimated seasonal transpiration was low, about 70 mm when estimated exclusively for trees in the forest interior and 107 mm when estimated exclusively for trees at the forest edge. This illustrates the likely magnitude of water use enhancement resulting from the conditions specific to the forest edge.
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Oogathoo, Shalini, Louis Duchesne, Daniel Houle et Daniel Kneeshaw. « Characterizing Seasonal Radial Growth Dynamics of Balsam Fir in a Cold Environment Using Continuous Dendrometric Data : A Case Study in a 12-Year Soil Warming Experiment ». Sensors 22, no 14 (9 juillet 2022) : 5155. http://dx.doi.org/10.3390/s22145155.
Texte intégralRésumé :
Historical temperature records reveal that the boreal forest has been subjected to a significant lengthening of the thermal growing season since the middle of the last century, and climate models predict that this lengthening will continue in the future. Nevertheless, the potential phenological response of trees to changes in growing season length remains relatively undocumented, particularly for evergreen boreal tree species growing in cold environments. Here, we used the recently defined zero growth (ZG) concept to extract and characterize the metrics of seasonal radial growth dynamics for 12 balsam fir trees subjected to a 12-year soil warming experiment using high resolution radius dendrometer measurements. The ZG concept provides an accurate determination of growth seasonality (onset, cessation, duration, growth rates, and total growth) for these slow-growing trees characterized by significant shrinkage in tree diameter due to dehydration in the winter. Our analysis revealed that, on average, growth onset starts at day 152 ± 7 (±1 SE, 31 May–1 June) and ceases at day 244 ± 27 (31 August–1 September), for a growing season duration of about 3 months (93 ± 26 days) over a 12-year period. Growing season duration is mainly determined by growth cessation, while growth onset varies little between years. A large part (80%) of the total growth occurs in the first 50 days of the growing season. Given the dynamics of growth, early growth cessation (shorter growing season) results in a higher average seasonal growth rate, meaning that longer growing seasons are not necessarily associated with greater tree growth. Soil warming induces earlier growth cessation, but increases the mean tree growth rate by 18.1% and the total annual growth by 9.1%, on average, as compared to the control trees. Our results suggest that a higher soil temperature for warmed trees contributes to providing better growth conditions and higher growth rates in the early growing season, when the soil temperature is low and the soil water content is elevated because of snowmelt. Attaining a critical soil temperature earlier, coupled with lower soil water content, may have contributed to the earlier growth cessation and shorter growing season of warmed trees.