Segui questo link per vedere altri tipi di pubblicazioni sul tema: Defoliation Measurement.
Articoli di riviste sul tema "Defoliation Measurement"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Defoliation Measurement".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.
1
Hunt, Thomas E., Fikru J. Haile, W. Wyatt Hoback e Leon G. Higley. "Indirect Measurement of Insect Defoliation". Environmental Entomology 28, n. 6 (1 dicembre 1999): 1136–39. http://dx.doi.org/10.1093/ee/28.6.1136.
Testo completo
2
Taylor, Sarah L., e David A. MacLean. "Validation of Spruce Budworm Outbreak History Developed from Aerial Sketch Mapping of Defoliation in New Brunswick". Northern Journal of Applied Forestry 25, n. 3 (1 settembre 2008): 139–45. http://dx.doi.org/10.1093/njaf/25.3.139.
Testo completoAbstract (sommario):
Abstract Aerial sketch mapping (ASM) of annual defoliation provides a means to quantify spruce budworm (Choristoneura fumiferana Clem.) outbreak histories, but accuracy is affected by factors such as navigation and weather conditions. We used ground-based defoliation estimates from 123 permanent sample plots (PSP) in New Brunswick and increment core growth data from a subset of PSPs, to validate ASM estimates of defoliation. From 1985 to 1993, 85% of 332 cases were correctly classified by aerial estimates as nil–light (0–30%) or moderate–severe (31–100%), with the proportion correct varying by measurement year, defoliation severity, and host species. Growth indices generated from 81 visually cross-dated and verified balsam fir (Abies balsamea [L.] Mill.) tree-ring series in 23 PSPs were significantly negatively correlated with aerial-derived cumulative defoliation for 87% of the PSPs, and correlation increased when aerial estimates were combined with ground survey data. We conclude that aerial surveys provide a reasonable estimate of defoliation history to estimate growth reduction.
3
Zeide, Boris, e Lynne C. Thompson. "Impact of Spring Sawfly Defoliation on Growth of Loblolly Pine Stands". Southern Journal of Applied Forestry 29, n. 1 (1 febbraio 2005): 33–39. http://dx.doi.org/10.1093/sjaf/29.1.33.
Testo completoAbstract (sommario):
Abstract To estimate the impact of a single spring defoliation by loblolly pine sawfly (Neodiprion taedae linearis Ross), diameters of 3,006 loblolly pines from five locations in southeastern Arkansas were measured immediately after defoliation and two more times at 1-year intervals.The proportion of defoliation was assessed at each measurement. An insecticide was used in an attempt to prevent defoliation in subsequent years. Because tree growth depends on many factors, a multivariate multiple regression model was used to separate these effects. The model predicts thata single defoliation reduces annual diameter and volume increment by 17.4, 8.4, and 2.8% for the first, second, and third years after defoliation, respectively (the actual loss was 18.9 and 8.9% for the first 2 years). It was found that trees defoliated 20–40% actuallygrew faster than undefoliated trees. This response, called overcompensation, is a common reaction of plants to moderate stress. Potential losses from defoliation are greatest in sawtimber-sized stands between the ages of 25 and 35 years. The decision to control sawflies should take into accountstand age and time to final harvest. South. J. Appl. For. 29(1):33–39.
4
Rast, Everette D., e Robert L. Brisbin. "Six-Year Effects of Two Late Spring Frosts on Appalachian Hardwoods". Northern Journal of Applied Forestry 4, n. 1 (1 marzo 1987): 26–28. http://dx.doi.org/10.1093/njaf/4.1.26.
Testo completoAbstract (sommario):
Abstract Severe late spring frosts can kill new shoots and leaves on commercial tree species at higher elevations. A previous short-term study has shown that the resulting defoliation and dieback does not seriously affect the radial growth or mortality of most species except American beech. In this study we found that defoliation, dieback, and radial growth increment were related to species and crown class. The radial growth increment of American beech was reduced to 70% of the previous 6-yr growth during the first year after the frost. The annual growth then increased consistently over the measurement period. Black cherry and sugar maple radial increment was only reduced to 88% of the previous 6-yr growth, but subsequent increments were much more variable. Epicormic branching on the lower bole of black cherry and beech increased significantly after defoliation occurred. At elevations above 3,200 ft, managers should discourage beech regeneration if timber production is the primary management objective. The potential for higher value products may be reduced because of increased variability in growth rate. North. J. Appl. For. 4:26-28, March 1987.
5
Nowakowska, Justyna Anna, Marcin Stocki, Natalia Stocka, Sławomir Ślusarski, Miłosz Tkaczyk, João Maria Caetano, Mirela Tulik, Tom Hsiang e Tomasz Oszako. "Interactions between Phytophthora cactorum, Armillaria gallica and Betula pendula Roth. Seedlings Subjected to Defoliation". Forests 11, n. 10 (19 ottobre 2020): 1107. http://dx.doi.org/10.3390/f11101107.
Testo completoAbstract (sommario):
The purpose of this study was to better understand the interactive impact of two soil-borne pathogens, Phytophthora cactorum and Armillaria gallica, on seedlings of silver birch (Betula pendula Roth.) subjected to stress caused by mechanical defoliation, simulating primary insect feeding. This is the first experimental confirmation of silver birch seedling root damage (and in consequence shoot mortality) caused by the additive effect of defoliation stress and P. cactorum inoculation via soil. However, the most severe damage to roots occurred after A. gallica inoculation. One year after treatments, chlorophyll fluorescence measurement, and gas chromatography coupled with mass spectrometry (GC-MS) were used to analyze the photosynthetic activity in leaves, the volatile organic compounds (VOCs) emitted by the birch leaves, and chemical compounds from the roots. The cumulative effect of the two pathogens and partial defoliation reduced photosynthetic activity, suggesting dysfunction of photosystem PSII due to the applied stresses. In summary, it seems that the main differences in photosynthetic performance could be attributed to Armillaria infection. The birch leaves in seedlings exposed to 50% defoliation, and inoculation with P.cactorum and A. gallica, emitted more aromatic carbonyls and alcohols, as well as half as much aliphatic esters, compared to controls. In infected birch roots, the production of phenols, triterpenes, and fatty alcohols increased, but fatty acids decreased. Higher levels of aromatic carbonyls and alcohols in leaves, as well as phenolic compounds in the roots of stressed birches (compared to control) suggest an activation of plant systemic acquired resistance (SAR).
6
Buonaccorsi, John P. "Prediction in the Presence of Measurement Error: General Discussion and an Example Predicting Defoliation". Biometrics 51, n. 4 (dicembre 1995): 1562. http://dx.doi.org/10.2307/2533288.
Testo completo
7
MacKinnon, Wayne E., e David A. MacLean. "Effects of surrounding forest and site conditions on growth reduction of balsam fir and spruce caused by spruce budworm defoliation". Canadian Journal of Forest Research 34, n. 11 (1 novembre 2004): 2351–62. http://dx.doi.org/10.1139/x04-115.
Testo completoAbstract (sommario):
The species composition of surrounding forest and site characteristics have been postulated to influence growth loss caused by eastern spruce budworm (Choristoneura fumiferana Clem.) defoliation. Forty spruce (Picea spp.) and balsam fir (Abies balsamea (L.) Mill.) stands located in north-central New Brunswick, Canada, were measured for defoliation and tree growth and used to determine the effects of surrounding forest (softwood, mixedwood), site (wet soil nutrient poor; moist soil nutrient rich), and species group (balsam fir, spruce) on growth reduction caused by spruce budworm. Stem analysis of six trees per stand (total 240 trees) determined mean specific volume increment (SVI) per year in 19731993. There was relatively little defoliation during the 19891993 measurement period, and regression analyses showed that SVI was significantly (p = 0.0299) related to mean defoliation for only one of eight treatment classes: balsam fir on moistrich sites in mixedwood forests. However, two periods of earlier growth reduction were evident, and analysis of variance showed that balsam fir on wetpoor sites sustained 12% greater (p = 0.0071) reduction in SVI from 1987 to 1990 than balsam fir on moistrich sites. White spruce (Picea glauca (Moench) Voss) sustained 13% greater (p = 0.0198) reduction in SVI from 1973 to 1978 than red spruce (Picea rubens Sarg.) black spruce (Picea mariana (Mill.) BSP). Surrounding forest type did not significantly affect SVI reduction from 1973 to 1978 or from 1987 to 1990, but from 1973 to 1978 stands in softwood forest sustained 5%8% more growth reduction than those in mixedwood forest.
8
Johnson, Lee F., e Lars L. Pierce. "Indirect Measurement of Leaf Area Index in California North Coast Vineyards". HortScience 39, n. 2 (aprile 2004): 236–38. http://dx.doi.org/10.21273/hortsci.39.2.236.
Testo completoAbstract (sommario):
The performance of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) for indirect measurement of leaf area index (LAI) was evaluated in vineyards of California's North Coast region. Twelve plots were established, representing vineyards of differing trellis, cultivar, and planting density. Mean LAI ranged from 0.5- to 2.25-m2 leaf area per m2 ground area by direct measurement (defoliation). Indirect LAI derived by a standard two-azimuth, diagonal-transect measurement protocol was significantly related to direct LAI (r2 = 0.78, P ≤ 0.001). However, the PCA underestimated direct LAI by about a factor of two. Narrowing the instrument's conical field of view from 148° to 56° increased indirect LAI by 13% to 60% in vertically trained plots, but still resulted in substantial underestimation of direct values. Use of this PCA protocol in vineyards should therefore be accompanied by direct measurement for calibration purposes.
9
Pethybridge, Sarah J., Frank Hay, Paul Esker, Calum Wilson e Forrest W. Nutter. "Use of a Multispectral Radiometer for Noninvasive Assessments of Foliar Disease Caused by Ray Blight in Pyrethrum". Plant Disease 91, n. 11 (novembre 2007): 1397–406. http://dx.doi.org/10.1094/pdis-91-11-1397.
Testo completoAbstract (sommario):
Foliar disease due to ray blight (Phoma ligulicola) in pyrethrum was quantified at three locations over 2 years in Tasmania, Australia. To obtain a range of ray blight disease intensities, replicated plots were treated with fungicides that varied in efficacy to control ray blight. Visual disease assessments and measurement of canopy reflectance were made at least once during spring (September through December). Visual assessments involved removal of flowering stems at ground level from which measurements of defoliation severity and the incidence of stems with ray blight were obtained. Reflectance of sunlight from pyrethrum canopies was measured at 485, 560, 660, 830, and 1,650 nm using a handheld multispectral radiometer. Measurements from these wavelengths also were used to calculate all possible reflectance ratios, as well as four vegetative indices. Relationships between wavelength bands, reflectance ratios, vegetative indices, and disease intensity measures were described by linear regression analyses. Several wavelength bands, ratios, and vegetative indices were significantly related in a linear fashion to visual measures of disease intensity. The most consistent relationships, with high R2 and low coefficients of variation values, varied with crop growth stage over time. The ratio 830/560 was identified as the best predictor of stem height, defoliation severity, and number of flowers produced on each stem in October. However, reflectance within the near-infrared range (830 nm) and the difference vegetative index was superior in November. The use of radiometric assessment of disease was noninvasive and provided savings in disease assessment time, which is critical where visual assessment is difficult and requires destructive sampling, as with pyrethrum.
10
Varago, André Luiz, Idemir Citadin, Marcos Robson Sachet, Gener Augusto Penso e Maria do Carmo Bassols Raseira. "Heritability of peach tree resistance to bacterial leaf spot". Pesquisa Agropecuária Brasileira 52, n. 5 (maggio 2017): 366–69. http://dx.doi.org/10.1590/s0100-204x2017000500010.
Testo completoAbstract (sommario):
Abstract: The objective of this work was to evaluate the broad-sense heritability reaction to bacterial leaf spot (Xanthomonas arboricola pv. pruni), in peach tree populations obtained from directed crosses. Disease severity and defoliation of the genotypes were evaluated in field conditions, with posterior measurement of the healthy leaf area duration (HAD). The observed average heritability (0.51) indicates that the use of the evaluated genitors can be effective for the development of cultivars with higher resistance to the disease.
11
Wang, B., T. S. Zha, X. Jia, J. N. Gong, B. Wu, C. P. A. Bourque, Y. Zhang, S. G. Qin, G. P. Chen e H. Peltola. "Microtopographic variation in soil respiration and its controlling factors vary with plant phenophases in a desert–shrub ecosystem". Biogeosciences 12, n. 19 (8 ottobre 2015): 5705–14. http://dx.doi.org/10.5194/bg-12-5705-2015.
Testo completoAbstract (sommario):
Abstract. Soil respiration (Rs) and its biophysical controls were measured over a fixed sand dune in a desert–shrub ecosystem in northwest China in 2012 to explore the mechanisms controlling the spatial heterogeneity in Rs and to understand the plant effects on the spatial variation in Rs in different phenophases. The measurements were carried out on four slope orientations (i.e., windward, leeward, north- and south-facing) and three height positions on each slope (i.e., lower, upper, and top) across the phenophases of the dominant shrub species (Artemisia ordosica). Coefficient of variation (i.e., standard deviation/mean) of Rs across the 11 microsites over our measurement period was 23.5 %. Soil respiration was highest on the leeward slope, and lowest on the windward slope. Over the measurement period, plant-related factors, rather than microhydrometeorological factors, affected the microtopographic variation in Rs. During the flower-bearing phase, root biomass affected Rs most, explaining 72 % of the total variation. During the leaf coloration–defoliation phase, soil nitrogen content affected Rs the most, explaining 56 % of the total variation. Our findings highlight that spatial pattern in Rs was dependent on plant distribution over a desert sand dune, and plant-related factors largely regulated topographic variation in Rs, and such regulations varied with plant phenology.
12
Wang, B., T. S. Zha, X. Jia, J. N. Gong, B. Wu, C. P. A. Bourque, Y. Q. Zhang, S. G. Qin, G. P. Chen e H. Peltola. "Micro-topographic variation in soil respiration and its controlling factors vary with plant phenophases in a desert-shrub ecosystem". Biogeosciences Discussions 12, n. 12 (25 giugno 2015): 9465–95. http://dx.doi.org/10.5194/bgd-12-9465-2015.
Testo completoAbstract (sommario):
Abstract. Soil respiration (Rs) and its biophysical controls were measured over a fixed sand dune in a desert-shrub ecosystem in northwest China in 2012 to explore the mechanisms controlling the spatial heterogeneity in Rs and to understand the plant effects on the spatial variation in Rs in different phenophases. The measurements were carried out on four slope orientations (i.e., windward, leeward, north- and south-face) and three height positions on each slope (i.e., lower, upper, and top) across the phenophases of the dominant shrub species (Artemisia ordosica). Coefficient of variation (i.e., standard deviation/mean) of Rs across the 11 microsites over our measurement period was 23.5 %. Soil respiration was highest on the leeward slope, but lowest on the windward slope. Over the measurement period, plant-related factors, rather than micro-hydrometeorological factors, affected the topographic variation in Rs. During the flowering-bearing phase, root biomass affected Rs most, explaining 72 % of the total variation. During the leaf coloration-defoliation phase, soil nitrogen content affected Rs the most, explaining 56 % of the total variation. Our findings highlight that spatial pattern in Rs was dependent on plant distribution over a desert sand dune, and plant-related factors largely regulated topographic variation in Rs, and such regulations varied with plant phenology.
13
Singh, D. K., e P. W. G. Sale. "Defoliation frequency and the response by white clover to increasing phosphorus supply 1. Leaf dry matter yield and plant morphology responses". Australian Journal of Agricultural Research 48, n. 1 (1997): 111. http://dx.doi.org/10.1071/a96053.
Testo completoAbstract (sommario):
A glasshouse experiment was carried out to determine how an increasing P supply influences the growth and survival of white clover plants subjected to a range of defoliation frequencies. Treatments involved the factorial combination of P application rate (0, 30, 90, and 180 mg/pot) to a P-deficient Krasnozem soil and defoliation frequency (1, 2, or 4 defoliations over 36 days). The survival of P-deficient plants was threatened by the most frequent defoliation; their leaf area declined owing to a reduction in leaf number and individual leaf size with each successive defoliation. Increasing the P supply to 180 mg/pot reversed this downward trend as the high P plants were able to maintain leaf area by increasing leaf size and number. Increasing the frequency from 1 to 4 defoliations over the 36 days also changed the form of the leaf dry matter response to added P, from an asymptotic to a linear response. The P requirement of white clover for maximum leaf yield therefore increased under frequent defoliation. This effect was also apparent for a range of morphological measurements including stolon elongation rate, leaf area, root mass, leaf number, and stolon number, where the magnitude of the P response was consistently greater for frequently defoliated plants. Exceptions included stolon mass, which responded more to P addition under infrequent defoliation.
14
Anderson, M. C., W. L. Bland, J. M. Norman e G. D. Diak. "Canopy Wetness and Humidity Prediction Using Satellite and Synoptic-Scale Meteorological Observations". Plant Disease 85, n. 9 (settembre 2001): 1018–26. http://dx.doi.org/10.1094/pdis.2001.85.9.1018.
Testo completoAbstract (sommario):
A method for predicting canopy wetness and humidity from remotely-acquired meteorological and radiation data is described. This method employs a surface energy balance model to scale from the above-canopy macroclimate to in-canopy microclimate conditions. Above-canopy temperature, vapor pressure, and wind speed inputs were obtained from objective analyses of hourly measurements from the synoptic weather network, while downwelling long- and shortwave radiation forcings were estimated from standard satellite observations. Precipitation (irrigation + rainfall) was the only input acquired in-field. Model predictions compared well with measurements of nighttime dew accumulation and relative humidity made in irrigated potato crops grown in central Wisconsin. Maximum dew amount measured in full canopies over four nights was reproduced to within 0.05 to 0.1 mm. The practical utility of this method to disease management was assessed by processing modeled and measured canopy microclimate data from two weather stations over three growing seasons through the BLITECAST disease forecasting system. Given the uncertainties inherent in the measurement of humidity, the model reasonably reproduced disease severity values generated from in-situ measurements in all but one case, where the canopy had suffered partial defoliation. Because the model simulates the microclimate within a healthy, uniform canopy, it may in many cases produce more reliable regional forecasts for plant disease than would a single set of in-situ measurements.
15
Shepherd, R. F., e T. G. Gray. "A SAMPLING SYSTEM FOR EGGS OF WESTERN BLACKHEADED BUDWORM, ACLERIS GLOVERANA (WALSINGHAM) (LEPIDOPTERA: TORTRICIDAE), ON WESTERN HEMLOCK, TSUGA HETEROPHYLLA (RAF.) SARG." Canadian Entomologist 122, n. 3 (giugno 1990): 555–62. http://dx.doi.org/10.4039/ent122555-5.
Testo completoAbstract (sommario):
AbstractEggs of western blackheaded budworm, Acleris gloverana (Walsingham), are laid on the lower surface of western hemlock, Tsuga heterophylla (Raf.) Sarg., needles. A comparison was made of the following measures of sample branch size as a basis for expressing egg density: fresh branch weight, branch area, total twig length, branch volume, and number of buds. The criteria for selection of these measures were as follows: correlations of branch size with dry needle weight, variances of egg density and their relative contribution to sample size, and ease of measurement. Fresh branch weight was the best choice. A sequential sampling system was developed on this basis and was related to a scale of predicted defoliation. In addition, a transformation was provided for use in data analysis.
16
Kotlarz, Jan, Mariusz Kacprzak, Karol Rotchimmel e Miłosz Tkaczyk. "The impact of the type of undergrowth on the remote sensing defoliation measurement of Quercus robur L. in the range: 640-820 nm". Pomiary Automatyka Robotyka 22, n. 1 (14 marzo 2018): 5–10. http://dx.doi.org/10.14313/par_227/5.
Testo completo
17
Bellingham, P. J., E. V. J. Tanner, P. M. Rich e T. C. R. Goodland. "Changes in light below the canopy of a Jamaican montane rainforest after a hurricane". Journal of Tropical Ecology 12, n. 5 (settembre 1996): 699–722. http://dx.doi.org/10.1017/s0266467400009883.
Testo completoAbstract (sommario):
ABSTRACTHurricane Gilbert caused disturbance to Jamaican montane rainforests in 1988. This study provides a detailed characterization of landscape-level changes in light below the canopy of these forests after the hurricane. Hemispherical photographs were taken below the forest canopy at four sites at permanent points 1 m above the ground between 7 and 33 mo after the hurricane. For each photograph photosynthetically active radiation (PAR) was computed. PAR declined exponentially in all sites during the period of measurement. During the first 24 mo after the hurricane, PAR beneath the canopy was significantly greater in sites that had been defoliated during the hurricane than in sites where few trees had been defoliated. By 28 mo after the hurricane there was no significant difference in PAR beneath the canopy among the four sites. By 33 mo after the hurricane canopy recovery was nearly complete and PAR was only slightly higher than measurements made before the hurricane. Our results were compared with studies of changes in light environment resulting from treefall gaps and under deciduous canopies. PAR during the first 18 mo after the hurricane was similar to that recorded in small canopy gaps in other forests. Widespread defoliation caused by hurricanes can thus increase PAR beneath the canopy over large areas and consequently opportunities may arise for widespread recruitment of tree species in response to increased light levels.
18
Lowe, KF, e TM Bowdler. "Effects of height and frequency of defoliation on the productivity of irrigated oats (Avena strigosa cv. Saia) and perennial ryegrass (Lolium perenne cv. Kangaroo Valley), grown alone or with barrel medic (Medicago truncatula cv. Jemalong)". Australian Journal of Experimental Agriculture 28, n. 1 (1988): 57. http://dx.doi.org/10.1071/ea9880057.
Testo completoAbstract (sommario):
The effects of varying the height (5- 10 cm) and frequency (2-6 weeks) of defoliation on the dry matter yield, numbers of plants and tillers, and forage quality of Avena strigosa cv. Saia (oats) and Lolium perenne cv. Kangaroo Valley (perennial ryegrass), grown both in pure swards and in combination with Medicago truncatula cv. Jemalong (barrel medic) were evaluated in irrigated pastures at Gatton in southeastern Queensland in 3 experiments over 2 years. In pure swards, defoliation every 6 weeks at the lowest cutting height (5 cm) gave the highest yields of both oats (10 t DM/ha) and ryegrass (12.6 t DM/ha). There were fewer live tillers per m2 of both oats and ryegrass cut at 6-week intervals compared with more frequent defoliations. However, tiller numbers of both were unaffected by cutting height. Lengthening the regrowth period from 2 to 6 weeks reduced nitrogen concentration by 23% (from 4, 75%) for ryegrass and by 16% (from 4.22%) for oats but increased cell wall content of oats from 38 to 45% and ryegrass from 36 to 41%. In vitro digestibility of oats fell from 82.4 to 79.9%, but the digestibility of ryegrass was unaffected. Cutting height had no effect on these measurements for either forage. In mixtures, ryegrass DM yield was highest (3.6 t/ha) when cut every 3 weeks and at the lowest defoliation height (5 cm) whereas cutting at 6-week intervals gave the highest yields of oats (5.2 t/ha). Legume yield was usually highest with defoliations every 3 or 4 weeks and at the lowest cutting height (5 cm), and was higher when grown with ryegrass (4.4 t/ha) than with oats (4.0 t/ha).
19
Fernandez, R. Thomas, Robert E. Schutzki e Kelly J. Prevete. "Influence of Spring and Fall Drought Stresses on Growth and Gas Exchange during Stress and Posttransplant of Container-grown Magnoli ×soulangiana `Jane'". Journal of the American Society for Horticultural Science 127, n. 1 (gennaio 2002): 38–44. http://dx.doi.org/10.21273/jashs.127.1.38.
Testo completoAbstract (sommario):
Responses of Magnolia ×soulangiana (Soul.-Bod.) `Jane' (`Jane' saucer magnolia) to consecutive short term pretransplant drought stresses and recovery after transplanting were evaluated beginning October 1997 and June 1998. Plants were subjected to one (mild) or two (moderate) 3-day drought stress periods or a two 3-day and one 4-day (severe) drought stress period, each separated by two rewatering periods over 24 hours. One day after each stress period, plants were transplanted into the field and well watered to monitor recovery from stress. Plant response was determined by measuring whole-plant CO2 assimilation, leaf gas exchange (CO2 assimilation, transpiration, stomatal conductance) and canopy growth throughout stress and recovery periods. Whole-plant and leaf CO2 assimilation were lower for the stressed treatments for most of the measurements taken during stress in the fall and spring. After release from stress and transplanting, leaf CO2 assimilation returned to control levels for mild and moderate fall stresses within 2 to 3 d by the next measurement, while it was over 3 weeks until recovery from the severe stress. There was no difference in leaf gas exchange following release from stress and transplanting during the spring stress. More rapid defoliation occurred for the severe fall-stressed plants compared to the controls after release from stress in the fall. Flower number was reduced in spring for the fall-stressed plants. At termination of the experiment, the growth index was lower for severe fall-stressed plants but there were no differences for other fall stress treatments. There was no increase in growth for control or stressed plants for the spring experiment.
20
H�gh-Jensen, H., e J. K. Schjoerring. "Measurement of biological dinitrogen fixation in grassland: Comparison of the enriched 15N dilution and the natural 15N abundance methods at different nitrogen application rates and defoliation frequencies". Plant and Soil 166, n. 2 (ottobre 1994): 153–63. http://dx.doi.org/10.1007/bf00008328.
Testo completo
21
Wilen, Cheryl A., e Jodie S. Holt. "Spatial Growth of Kikuyugrass (Pennisetum clandestinum)". Weed Science 44, n. 2 (giugno 1996): 323–30. http://dx.doi.org/10.1017/s0043174500093954.
Testo completoAbstract (sommario):
Photographic techniques and the point-frame transect method were used to study areal growth of kikuyugrass grown in the field without competition in 1990 and 1991. The effect of cutting height on plant extension was also examined in 1991. There were no differences in sward area between eight selections planted in 1990, except on the first measurement date, but selections differed in height and number of primary and secondary stolons. Expansion was irregular in all but one selection, and the patch shape of all irregular selections was defined by the direction and number of the earliest buds to sprout from the stolons. Only two of the eight selections were planted in 1991. Cutting height affected extension from the plot center, linear plant frequency, and plant biomass. The lowest height of cut, 2.5 cm, had the least extension and frequency, the higher cut, 5 cm, was intermediate, and the unmowed plots had the highest extension and frequency. There were differences between selections in number of nodes per unit area, which resulted in differences in response to mowing. Results from a greenhouse clipping experiment showed that although root weight of stolon sections used as propagules was reduced by defoliation, starch content was not affected. The spreading ability of kikuyugrass appears to be based on its ability to branch from its stolons presumably due to reallocation of resources. Based on these results, close mowing could slow the process of kikuyugrass invasion into other turf species but is inadequate to control it.
22
Jenicek, Michal, Hana Pevna e Ondrej Matejka. "Canopy structure and topography effects on snow distribution at a catchment scale: Application of multivariate approaches". Journal of Hydrology and Hydromechanics 66, n. 1 (1 marzo 2018): 43–54. http://dx.doi.org/10.1515/johh-2017-0027.
Testo completoAbstract (sommario):
Abstract The knowledge of snowpack distribution at a catchment scale is important to predict the snowmelt runoff. The objective of this study is to select and quantify the most important factors governing the snowpack distribution, with special interest in the role of different canopy structure. We applied a simple distributed sampling design with measurement of snow depth and snow water equivalent (SWE) at a catchment scale. We selected eleven predictors related to character of specific localities (such as elevation, slope orientation and leaf area index) and to winter meteorological conditions (such as irradiance, sum of positive air temperature and sum of new snow depth). The forest canopy structure was described using parameters calculated from hemispherical photographs. A degree-day approach was used to calculate melt factors. Principal component analysis, cluster analysis and Spearman rank correlation were applied to reduce the number of predictors and to analyze measured data. The SWE in forest sites was by 40% lower than in open areas, but this value depended on the canopy structure. The snow ablation in large openings was on average almost two times faster compared to forest sites. The snow ablation in the forest was by 18% faster after forest defoliation (due to the bark beetle). The results from multivariate analyses showed that the leaf area index was a better predictor to explain the SWE distribution during accumulation period, while irradiance was better predictor during snowmelt period. Despite some uncertainty, parameters derived from hemispherical photographs may replace measured incoming solar radiation if this meteorological variable is not available.
23
Williams, M. R., e I. Abbott. "Quantifying Average Defoliation Using Leaf-Level Measurements". Ecology 72, n. 4 (agosto 1991): 1510–11. http://dx.doi.org/10.2307/1941126.
Testo completo
24
Hillabrand, Rachel M., Uwe G. Hacke e Victor J. Lieffers. "Defoliation constrains xylem and phloem functionality". Tree Physiology 39, n. 7 (17 maggio 2019): 1099–108. http://dx.doi.org/10.1093/treephys/tpz029.
Testo completoAbstract (sommario):
AbstractInsect defoliation contributes to tree mortality under drought conditions. Defoliation-induced alterations to the vascular transport structure may increase tree vulnerability to drought; however, this has been rarely studied. To evaluate the response of tree vascular function following defoliation, 2-year-old balsam poplar were manually defoliated, and both physiological and anatomical measurements were made after allowing for re-foliation. Hydraulic conductivity measurements showed that defoliated trees had both increased vulnerability to embolism and decreased water transport efficiency, likely due to misshapen xylem vessels. Anatomical measurements revealed novel insights into defoliation-induced alterations to the phloem. Phloem sieve tube diameter was reduced in the stems of defoliated trees, suggesting reduced transport capability. In addition, phloem fibers were absent, or reduced in number, in stems, shoot tips and petioles of new leaves, potentially reducing the stability of the vascular tissue. Results from this study suggest that the defoliation leads to trees with increased risk for vascular dysfunction and drought-induced mortality through alterations in the vascular structure, and highlights a route through which carbon limitation can influence hydraulic dysfunction.
25
Jarocińska, Anna, Małgorzata Białczak e Łukasz Sławik. "Application of aerial hyperspectral images in monitoring tree biophysical parameters in urban areas". Miscellanea Geographica 22, n. 1 (30 marzo 2018): 56–62. http://dx.doi.org/10.1515/mgrsd-2017-0034.
Testo completoAbstract (sommario):
Abstract Monitoring of trees in urban areas can be conducted using remote sensing, but should be supported by field measurements. The article aims to present the research method used to evaluate discolouration and defoliation of trees and tree damage in the city of Białystok in Poland. The analyses were done using AISA hyperspectral images. Field measurements encompassed determining the locations, species and levels of discolouration and defoliation of trees. Remote sensing indices of vegetation were calculated and correlated with the field-measured values of discolouration and defoliation. Based on that, values of discolouration and defoliation were calculated and evaluated against the field studies. The RMSE of the acquired data was around 16%. Using parameter values, a map of tree damage was drawn up. Based on the analysis, it can be stated that a significant number of trees is undamaged, although a large portion of the trees falls into the warning class.
26
Jordan, B. S., W. D. Branch, A. W. Coffin, C. M. Smith e A. K. Culbreath. "Comparison of Trimble GreenSeeker and Crop Circle (Model ACS-210) Reflectance Meters for Assessment of Severity of Late Leaf Spot". Peanut Science 46, n. 2 (1 luglio 2019): 110–17. http://dx.doi.org/10.3146/ps18-19.1.
Testo completoAbstract (sommario):
ABSTRACT Four field experiments conducted in 2015 were used to examine the relationships among normalized difference vegetation index (NDVI) measurements from two canopy crop sensors and visual estimates of defoliation by late leaf spot (Nothopassalora personata) of peanut (Arachis hypogaea) the predominant foliar disease in this study. For each evaluation, reflectance was measured with each the two meters, and leaf spot severity was measured visually within as short a time as possible. Linear and quadratic regression models were used to characterize the relationships between percent defoliation from late leaf spot and NDVI measured with the GreenSeeker (NDVIGS) and Crop Circle (NDVICC) instruments and the relationships between NDVIGS and NDVICC. NDVIGS decreased with increasing percent defoliation according to linear or quadratic functions in three of the four trials, NDVICC decreased with increasing percent defoliation according to linear functions in three of four trials. In two of the four trials, NDVICC increased with increasing NDVIGS according to quadratic functions, but there was no significant regression for those variables in two trials. In three of the four trials, NDVICC linear regression had a better fit for predicting percent defoliation according to the coefficient of determination (R2). There was no indication for either instrument that the same NDVI reading corresponded with the same level of defoliation across trials. Results indicated that NDVI measurements from the two instruments are not interchangeable.
27
Liebhold, Andrew M., Edward E. Simons, Alan Sior e James D. Unger. "Forecasting Defoliation Caused by the Gypsy Moth from Field Measurements". Environmental Entomology 22, n. 1 (1 febbraio 1993): 26–32. http://dx.doi.org/10.1093/ee/22.1.26.
Testo completo
28
Lyytikäinen-Saarenmaa, P., e E. Tomppo. "Impact of sawfly defoliation on growth of Scots pine Pinus sylvestris (Pinaceae) and associated economic losses". Bulletin of Entomological Research 92, n. 2 (aprile 2002): 137–40. http://dx.doi.org/10.1079/ber2002154.
Testo completoAbstract (sommario):
AbstractNeedle defoliation by diprionid sawflies decreases the increment and timber yield of Scots pine Pinus sylvestris L. The aim of this study was to provide approximate estimates of this decrease and preliminary estimates of the economic value of growth losses and tree mortality. Growth loss after needle damage by Diprion pini(Linnaeus) was studied in western Finland. Increment cores were sampled for radial growth measurements from trees subjected to slight, moderate and heavy defoliation. A literature survey was carried out to estimate radial growth losses after defoliation by Neodiprion sertifer (Geoffroy). Calculations for economic consequences were based on previous estimates and on the ongoing 9th Finnish National Forest Inventory. Moderate defoliation by N. sertifer and D. pini reduced volume growth by 21% and 86% and heavy defoliation by 38% and 94%, respectively. Tree mortality in defoliated stands was recorded as approximately 4%after an outbreak of N. sertifer and 30% after an outbreak of D. pini. The estimated average economic value of the losses due to reduced growth and tree mortality reached $40 ha−1 after a single-year outbreak of N. sertifer and $310 ha−1 in the case of D. pini. These preliminary estimates of economic losses indicate a much higher impact of pine sawflies than those revealed by the few earlier studies in Europe.
29
Lampíř, Lubomír, e Jiří Źaloudek. "Influence of summer management practices and date of harvesting on organic acids concentration and sugar concentration in grapes of Vitis vinifera L., cv. Riesling". Horticultural Science 45, No. 4 (10 dicembre 2018): 211–18. http://dx.doi.org/10.17221/213/2017-hortsci.
Testo completoAbstract (sommario):
The impact of summer canopy management was investigated in Vitis vinifera L., cv. Riesling. Sugar and organic acid concentrations were measured for the six defoliation treatments. Titratable acidity (TA) was measured twice before harvest and once at the date of harvest. The same measurements were done twice during wine ageing. The young wine was measured for concentrations of malic, tartaric and volatile acids. Treatments with appropriate defoliation, where shortened lateral shoots (up to two leaves) were retained, supported the process of wine grape ripening to the greatest extend in the cool climate of the Czech Republic, while treatments with almost no defoliation yielded the worst results. The TA decreased during fruit ripening after veraison and continued to decrease during wine maturation. The tendency of decreasing with time was shown for the malic to tartaric acid ratio as well. Concentrations of volatile acids were sufficiently low in each of the treatments.
30
Fulmer, Abraham M., Lucky K. Mehra, Robert C. Kemerait, Timothy B. Brenneman, Albert K. Culbreath, Katherine L. Stevenson e Emily G. Cantonwine. "Relating Peanut Rx Risk Factors to Epidemics of Early and Late Leaf Spot of Peanut". Plant Disease 103, n. 12 (dicembre 2019): 3226–33. http://dx.doi.org/10.1094/pdis-10-18-1782-re.
Testo completoAbstract (sommario):
Previous research has demonstrated the efficacy of prescription fungicide programs, based upon Peanut Rx, to reduce combined effects of early leaf spot (ELS), caused by Passalora arachidicola (Cercospora arachidicola), and late leaf spot (LLS), caused by Nothopassalora personata (syn. Cercosporidium personatum), but the potential of Peanut Rx to predict each disease has never been formally evaluated. From 2010 to 2016, non-fungicide-treated peanut plots in Georgia and Florida were sampled to monitor the development of ELS and LLS. This resulted in 168 cases (unique combinations of Peanut Rx risk factors) with associated total leaf spot risk points ranging from 40 to 100. Defoliation ranged from 13.9 to 100%, and increased significantly with increasing total risk points (conditional R2 = 0.56; P < 0.001). Leaf spot onset (time in days after planting [DAP] when either leaf spot reached 1% lesion incidence), ELS onset, and LLS onset ranged from 29 to 140, 29 to 142, and 50 to 143 DAP, respectively, and decreased significantly with increasing risk points. Standardized AUDPC of ELS was significantly affected by risk points (conditional R2 = 0.53, P < 0.001), but not for LLS. After removing redundant Peanut Rx factors, planting date, rotation, historical leaf spot prevalence, cultivar, and field history were used as fixed effects in mixed effect regression models to evaluate their contribution to leaf spot, ELS or LLS prediction. Results from mixed effects regression confirmed that the selected Peanut Rx risk factors contributed to the variability of at least one measurement of development of combined or separate epidemics of ELS and LLS, but not all factors affected ELS and LLS equally. Historical leaf spot prevalence, a new potential preplant risk factor, was a consistent predictor of the dominant disease(s) observed in the field. Results presented here demonstrate that Peanut Rx is a very effective tool for predicting leaf spot onset regardless of which leaf spot is predominant, but also suggest that associated risk does not reflect the same development for each disease. These data will be useful for refining thresholds for differentiating high, moderate, and low risk fields, and reevaluating the timing of fungicide applications in reduced input programs with respect to disease onset.
31
Guerra-Hincapié, Juan José, Óscar De Jesús Córdoba-Gaona, Juan Pablo Gil-Restrepo, Danilo Augusto Monsalve-García, Juan David Hernández-Arredondo e Enrique Guillermo Martínez-Bustamante. "Phenological patterns of defoliation and refoliation processes of rubber tree clones in the Colombian northwest". Revista Facultad Nacional de Agronomía Medellín 73, n. 3 (1 settembre 2020): 9293–303. http://dx.doi.org/10.15446/rfnam.v73n3.80546.
Testo completoAbstract (sommario):
The knowledge of the defoliation-refoliation process in rubber cultivation allows the development of management strategies in the production system to improve rubber yield. The objective of this study was to determine the intensity and duration of defoliation-refoliation of rubber clones FX 3864, IAN 710 and IAN 873 in the municipality of Tarazá and the FX 3864 and IAN 873 clones in the municipality of Nechí (northwestern Colombia). From October 2015 to June 2016, the measurements of the necromass were carried out in each location for each clone. The light environment was quantified, employing the hemispheric photographs technique to estimate canopy openness percentage (CO) and leaf area index. The assessed weeks were grouped by Principal Component Analysis (PCA) based on the original phenology and climatic variables. The defoliation-refoliation process was analyzed descriptively using graphical representations of the trend for the phenological variables that best described this process. The relationship between climatic and phenological variables in the period evaluated was evidenced; the rainfall was the most critical climatic characteristic in the induction of the defoliation process. The leaf area index was reduced to a minimum value in February, with values of 0.52 for IAN 710 clone in Tarazá, and 0.64 for the IAN 873 clone in Nechí, which corresponded to the highest defoliation stage in both locations. The refoliation period was short (4 to 6 weeks) and occurred during the dry season for all the clones in both places.
32
Clark, K. L., N. S. Skowronski, M. R. Gallagher, H. Renninger e K. V. R. Schäfer. "Contrasting effects of invasive insects and fire on ecosystem water use efficiency". Biogeosciences Discussions 11, n. 6 (20 giugno 2014): 9565–600. http://dx.doi.org/10.5194/bgd-11-9565-2014.
Testo completoAbstract (sommario):
Abstract. We used eddy covariance and meteorological measurements to estimate net ecosystem exchange of CO2 (NEEc), gross ecosystem production (GEP), evapotranspiration (Et), and ecosystem water use efficiency (WUEe) in three upland forests in the New Jersey Pinelands that were defoliated by Gypsy moth (Lymantria dispar L.) or burned using prescribed fire. Before disturbance daytime NEEc, daily GEP and daily WUEe during the summer were greater at an oak-dominated stand than at mixed or pine-dominated stands. Both defoliation and prescribed burning reduced stand leaf area and canopy nitrogen content. At the oak stand, daily GEP during the summer was only 35% of pre-disturbance values during complete defoliation in 2007, and then averaged 71% and 78% of pre-defoliation values one and two years following complete defoliation. Prescribed fires conducted in the dormant season at the mixed and pine-dominated stands reduced daily GEP during the summer to 79 and 82% of pre-disturbance periods during the following growing season. Daily GEP during the summer was a strong function of N content in foliage at the oak and mixed stands, but a weaker function at the pine-dominated stand. Ecosystem WUEe, calculated as GEP/Et during dry canopy conditions in the summer, was reduced to 60% and 46% of pre-disturbance values at the oak and mixed stands during defoliation, while prescribed fire had little effect on WUEe. Overall, our results indicate that WUEe during recovery is dependent on both the type and time since disturbance.
33
Cripps, M. G., C. A. Dowsett, S. D. Jackman, A. D. L. Noble e G. J. Houliston. "Genetic variation for tolerance to defoliation in Cirsium arvense (Californian thistle)". New Zealand Plant Protection 70 (31 luglio 2017): 324. http://dx.doi.org/10.30843/nzpp.2017.70.91.
Testo completoAbstract (sommario):
The pasture weed, Cirsium arvense (Californian thistle), is notorious for its ability to tolerate defoliation by herbivores, mowing, or herbicides, which is facilitated by the growth of adventitious shoots from its extensive clonal underground root system. In an outdoor potted-plant experiment, we examined the tolerance of 36 unique genotypes of C. arvense to defoliation by establishing pairs of clonal replicates that were assigned to a clipped, or unclipped treatment. Three clipping treatments were applied, and the final height, number of shoots, and biomass, were measured to compare the fitness between the clipped and unclipped clones. The majority of genotypes were negatively affected by clipping and showed a reduction in most final fitness measurements. However, some genotypes were equivalent or even greater than their unclipped counterparts indicating a large genetic range for tolerance to defoliation. The mean range in tolerance ratios (clipped/ unclipped) was 0.17 to 1.3 for shoot height, 0.26 to 1.2 for shoot density, and 0.6 to 1.2 for biomass (where a ratio of 1 indicates equivalence to the unclipped state). Since repeated defoliation is recommended for control of this weed, selection for more tolerant genotypes is possible, which may have management implications.
34
Hall, R. J., S. J. Titus e W. J. A. Volney. "Estimating top-kill volumes with large-scale photos on trees defoliated by the jack pine budworm". Canadian Journal of Forest Research 23, n. 7 (1 luglio 1993): 1337–46. http://dx.doi.org/10.1139/x93-171.
Testo completoAbstract (sommario):
The estimation of tree top-kill volumes is an important component of quantifying defoliation impact of severe budworm (Choristoneurapinus Freeman) defoliation on jack pine (Pinusbanksiana Lamb.) trees. Field survey is the only method by which this assessment is currently undertaken. This study evaluated an alternative methodology based on large-scale aerial photo (1:900) measurements and a taper model fitted for jack pine. This included generating linear models for the prediction of actual top-kill length from photo-measured top-kill length, the prediction of DBH from photo-measured tree height and crown area, and the estimation of top-kill volumes from a jack pine taper model. The set of three linear equations fitted with ordinary least squares resulted in top-kill volume estimates that showed no bias. The volume of damaged trees not visible on photographs was less than 1% of the volume of all damaged trees, and therefore adjustment for missed trees was not considered necessary. The methodology is convenient to implement, and if combined with forest sampling procedures, the projection of tree top-kill volumes to the stand level can provide an estimate of defoliation impact. The methodology is also potentially suitable for assessing other insect defoliation impacts that cause top kill.
35
Coffelt, Mark A., e Peter B. Schultz. "Relationship Among Orangestriped Oakworm (Lepidoptera: Saturniidae) Frass Length, Frass Production, Host Plant, and Defoliation". Journal of Entomological Science 28, n. 3 (1 luglio 1993): 291–98. http://dx.doi.org/10.18474/0749-8004-28.3.291.
Testo completoAbstract (sommario):
Defoliation of urban oak trees by the orangestriped oakworm, Anisota senatoria (J. E. Smith), and associated frass has become a significant problem in southeastern Virginia. Measurements of frass length and production provided a decision-making guideline for A. senatoria management. Frass length was used to differentiate A. senatoria instars reared on Q. palustris (Muenchhausen), pin oak. Host plants significantly affected A. senatoria frass length and production per larva and host plants should be considered when determining instars. Frass length was longer and frass production higher when larvae were reared on Q. nigra (water oak), Q. phellos (willow oak), Q. coccinea (scarlet oak), and Q. palustris compared with six other species. Frass length was shorter in second, fourth, and fifth instars when larvae were reared on Q. alba (white oak) compared with six, eight, and five other species, respectively. Landscape fabrics were used to collect frass and recovered 90% of all frass deposited. Frass production on small pin oaks (mean ht = 2.1 m, mean diameter at breast ht = 6.3 cm) was significantly correlated with defoliation. An aesthetic injury level of 25% defoliation resulted in frass collections of 2.2 g per tree.
36
Etgen, Robert J., e Ray R. Hicks. "Impact of Looper Defoliation: A Case Study in West Virginia". Northern Journal of Applied Forestry 4, n. 4 (1 dicembre 1987): 201–4. http://dx.doi.org/10.1093/njaf/4.4.201.
Testo completoAbstract (sommario):
Abstract In 1984, measurements of site and stand conditions and tree mortality were taken from 141 tenth-acre plots located within stands defoliated by loopers from 1981-1983, including 35 undefoliated control plots. Mortality due to loopers was expanded to the total defoliation area (1 million ac in 1981, 100 thousand in 1982, and 35 thousand in 1983). Loss due to mortality amounted to 2.3 billion board feet (bbf) of sawtimber and 4.2 million cords (cd) of pulpwood, with a total estimated stumpage value of about 345 million dollars. North. J. Appl. For. 4:201-204, December 1987.
37
Tyburski, Łukasz, e Paweł Przybylski. "Evaluation of the Loss of Assimilation Apparatus and Its Causes in Scots Pine Stands (Pinus Sylvestris L.) of the Kampinos National Park". Folia Forestalia Polonica 60, n. 3 (1 settembre 2018): 173–82. http://dx.doi.org/10.2478/ffp-2018-0017.
Testo completoAbstract (sommario):
Abstract The Kampinos National Park (KNP), in terms of ecology, is an exceptionally valuable place in the Polish lowland region. Until the 20th century, as a result of limited human influence on the natural resources of the Kampinos Forest, it can be presumed that the 100-year-old tree stands were shaped by natural ecological processes. This study contains a detailed assessment of crown conditions, dendrometric measurements and visible disease symptoms in the oldest fragments of the KNP, as well as statistical evaluation of the relationships between these factors. Results were correlated with ecological factors such as precipitation and temperature. For the purpose of the study, five tree stands, each over 130 years old, were selected. In each stand, the level of defoliation was assessed, based on the forest monitoring methodology performed in Poland for the State Environmental Monitoring. Tree height, circumference, and diameter at breast height measurements were performed for all the trees, and any visible disease symptoms were described. Defoliation data were used to classify 93.6% of the trees as the second level of stand damage (the so-called ‘warning’ level) according to the monitoring methodology. Observed disease factors confirm the physiological weakening of the trees. The populations studied exhibited a range of mean height and stem volume, and these were not significantly related to the level of defoliation or visible disease symptoms. Ecological factors, especially the drought in 2015, probably did not have a negative impact on the examined stands. The analysed pine populations demonstrate physiological weakness, but this appears to be related to their age and natural ecological processes.
38
Lorenz, Martin, e Volker Mues. "Forest Health Status in Europe". Scientific World JOURNAL 7 (2007): 22–27. http://dx.doi.org/10.1100/tsw.2007.17.
Testo completoAbstract (sommario):
Forest health status in Europe is assessed by the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). Established by the Convention on Long-Range Transboundary Air Pollution (CLRTAP) under the United Nations Economic Commission for Europe (UNECE), the ICP Forests has been monitoring forest condition in close cooperation with the European Commission (EC) for 20 years. The present paper describes the latest results of the deposition measurements on permanent monitoring plots and of the extensive defoliation sample survey. The findings reveal marked spatial patterns in bulk and throughfall depositions of nitrate (N-NO3-), ammonium (N-NH4+), and sulfate (S-SO42-), as well as an obvious decrease in bulk and throughfall deposition of sulfate. Latest analyses of defoliation data confirm previous results, indicating a high correlation with weather extremes.
39
Clark, K. L., N. S. Skowronski, M. R. Gallagher, H. Renninger e K. V. R. Schäfer. "Contrasting effects of invasive insects and fire on ecosystem water use efficiency". Biogeosciences 11, n. 23 (1 dicembre 2014): 6509–23. http://dx.doi.org/10.5194/bg-11-6509-2014.
Testo completoAbstract (sommario):
Abstract. We used eddy covariance and meteorological measurements to estimate net ecosystem exchange of CO2 (NEE), gross ecosystem production (GEP), evapotranspiration (Et), and ecosystem water use efficiency (WUEe; calculated as GEP / Et during dry canopy conditions) in three upland forests in the New Jersey Pinelands, USA, that were defoliated by gypsy moth (Lymantria dispar L.) or burned using prescribed fire. Before disturbance, half-hourly daytime NEE during full sunlight conditions, daily GEP, and daily WUEe during the summer months were greater at the oak-dominated stand compared to the mixed or pine-dominated stands. Both defoliation by gypsy moth and prescribed burning reduced stand leaf area and nitrogen mass in foliage. During complete defoliation in 2007 at the oak stand, NEE during full sunlight conditions and daily GEP during the summer averaged only 14 and 35% of pre-disturbance values. Midday NEE and daily GEP then averaged 58 and 85%, and 71 and 78% of pre-defoliation values 1 and 2 years following complete defoliation, respectively. Prescribed fires conducted in the dormant season at the mixed and pine-dominated stands reduced NEE during full sunlight conditions and daily GEP during the following summer to 57 and 68%, and 79 and 82% of pre-disturbance values, respectively. Daily GEP during the summer was a strong function of N mass in foliage at the oak and mixed stands, but a weaker function of N in foliage at the pine-dominated stand. Ecosystem WUEe during the summer at the oak and mixed stands during defoliation by gypsy moth averaged 1.6 and 1.1 g C kg H2O−1, representing 60 and 46% of pre-disturbance values. In contrast, prescribed fires at the mixed and pine-dominated stands had little effect on WUEe. Two years following complete defoliation by gypsy moth, WUEe during the summer averaged 2.1 g C kg H2O−1, 80% of pre-disturbance values. WUEe was correlated with canopy N content only at the oak-dominated stand. Overall, our results indicate that WUEe during and following non-stand replacing disturbance is dependent on both the type and time since disturbance.
40
Poff, Jonathan A., Oscar A. Balocchi e Ignacio F. López. "Sward and tiller growth dynamics of Lolium perenne L. as affected by defoliation frequency during autumn". Crop and Pasture Science 62, n. 4 (2011): 346. http://dx.doi.org/10.1071/cp10229.
Testo completoAbstract (sommario):
A mini-sward study was undertaken between January and September 2008 in Valdivia, Chile, to quantify and compare changes in the herbage production, growth dynamics and nutritive quality of a Lolium perenne sward during autumn in response to different nitrogen (N) application regimes and defoliation frequencies. The N levels used in the present study corresponded to the equivalent of an autumnal application of 0, 25 or 75 kg N/ha. The defoliation frequency was based on leaf regrowth stage, and corresponded to the time taken for 1.5, 2.5 or 3.5 leaves per tiller to expand. The growth dynamic measurements were also related to temperature. The results showed that the level of N had no effect on the studied variables. Plants defoliated at the 3.5-leaf stage showed a higher herbage production, higher tillering and a more balanced nutritional profile than plants cut at the 1.5-leaf stage. The defoliation interval had no effect on leaf elongation or leaf appearance. The leaf elongation rate was linearly related to the mean daily temperature (P < 0.01), and the accumulated leaf and tiller number showed a significant linear relationship (P < 0.01) with the thermal time expressed as growing degree days. From the defoliation frequencies tested here, we can conclude that the best time for grazing L. perenne swards during autumn is at the 3.5-leaf stage due to a higher herbage production, higher tillering rate, more balanced nutritive quality and higher reserve levels of the plant, which provide a more favourable background for subsequent growth.
41
Jakovljević, Tamara, Aldo Marchetto, Lucija Lovreškov, Nenad Potočić, Ivan Seletković, Krunoslav Indir, Goran Jelić et al. "Assessment of Atmospheric Deposition and Vitality Indicators in Mediterranean Forest Ecosystems". Sustainability 11, n. 23 (30 novembre 2019): 6805. http://dx.doi.org/10.3390/su11236805.
Testo completoAbstract (sommario):
Considering the fragility of the Mediterranean environment, there is an increasing need to improve the knowledge of this forest environment. The aim of this study was to examine the effects of air pollution on the forest ecosystem’s condition by analyzing tree vitality. The study area was chosen to represent the most important and the most common species in Mediterranean forest ecosystems of the Eastern Adriatic coast. Quercus pubescens, Quercus ilex, Pinus halepensis, and Pinus nigra plots were equipped with rain collectors and dendrometer bands. Sampling, measurements, and analyses of atmospheric deposition, foliar nutrient, defoliation, and growth were all carried out. Results showed that actual N deposition loads were the lowest in Aleppo pine forest and the highest in holm oak forests. This, however, did not have an effect on the concentrations of N in foliage. Most elements’ concentrations were in the plausible range. No relevant differences in mean defoliation between the plots were observed. The plots with a lower percentage of basal area increment (BAI%) were found to have lower defoliation. The research was conducted to bridge the gap in the knowledge of air pollutants and vitality indicators in different forest types. These findings are a valuable contribution to the sustainable forest management of Mediterranean forest.
42
Lawson, A. R., P. W. G. Sale e K. B. Kelly. "Effect of defoliation frequency on an irrigated perennial pasture in northern Victoria 2*Part 1, Aust. J. Agric. Res., 1997, 48, 811 - 17.. Individual plant morphology". Australian Journal of Agricultural Research 48, n. 6 (1997): 819. http://dx.doi.org/10.1071/a96089.
Testo completoAbstract (sommario):
The effect of 5 winter and 2 post-winter defoliation frequencies on the morphology of medium-leafed and large-leafed white clover and perennial ryegrass plants in an irrigated perennial pasture in northern Victoria was investigated. Measurements included leaf appearance rates, axillary bud development and survival, stolon elongation and survival, and tiller production and survival. White clover leaf appearance rate was affected little by either defoliation frequency or cultivar, ranging from 0·4 leaves/week in July to 1·1 leaves/week in February. In contrast, perennial ryegrass leaf appearance rate in the same period ranged from 0·35 to 0·7 leaves/week. Axillary bud production on clover stolons was highest in winter and spring and lowest through summer, and was usually greater in the medium-leafed than in the large-leafed cultivars. When the swards were not defoliated through winter, the rate of bud production was reduced in late winter; this was followed by a high rate of bud production in early spring, resulting in little treatment difference in the number of buds per stolon by mid spring. Bud survival was greater when initiated in winter than in summer. The rate of stolon death in spring was higher in the swards not defoliated during winter and higher in the large-leafed than in the medium-leafed cultivar. These effects were associated with the stolon elongation rate in late winter; the medium-leafed cultivar was unaffected by defoliation frequency, whereas in the large-leafed cultivars the rate of stolon elongation increased as the defoliation interval lengthened and canopy shading increased. Perennial ryegrass tiller production was greater with frequent than infrequent winter or post-winter defoliation, but never exceeded 1·2 daughter tillers/tiller, with 44% of the reproductive tillers failing to replace themselves. The low leaf appearance rate and tiller production of the perennial ryegrass may contribute to its poor competitiveness and persistence in this environment.
43
MacDougall, R. Glenn, David A. MacLean e Robert G. Thompson. "The use of electrical capacitance to determine growth and vigor of spruce and fir trees and stands in New Brunswick". Canadian Journal of Forest Research 18, n. 5 (1 maggio 1988): 587–94. http://dx.doi.org/10.1139/x88-085.
Testo completoAbstract (sommario):
A capacitance meter based on an integrating operational amplifier design was used to measure electrical capacitance of over 3400 trees in 90 spruce–fir stands in New Brunswick. Trends of capacitance were compared with trends of tree growth, tree characteristics, and defoliation by spruce budworm (Choristoneurafumiferana (Clem.)). Capacitance differed among tree species, with balsam fir (Abiesbalsamea (L.) Mill.) and white spruce (Piceaglauca (Moench) Voss) having generally higher values than red spruce (Picearubens Sarg.) and black spruce (Piceamariana (Mill.) B.S.P.). Capacitance also decreased with crown class and with increasing cumulative defoliation. Correlations between tree growth and capacitance ranged from about 0.6 to 0.7 for tree data, and 0.6 to 0.9 for stand data. Regressions between mean growth per stand and mean capacitance explained about 40 to 70% of the variability in growth. These results indicate that it is practical to use electrical capacitance measurements to assess tree growth and vigor.
44
Peters, Richard L., Jose Carlos Miranda, Leonie Schönbeck, Daniel Nievergelt, Marina V. Fonti, Matthias Saurer, Ana Stritih et al. "Tree physiological monitoring of the 2018 larch budmoth outbreak: preference for leaf recovery and carbon storage over stem wood formation in Larix decidua". Tree Physiology 40, n. 12 (27 luglio 2020): 1697–711. http://dx.doi.org/10.1093/treephys/tpaa087.
Testo completoAbstract (sommario):
Abstract Insect defoliation impacts forest productivity worldwide, highlighting the relevance of plant–insect interactions. The larch budmoth (Zeiraphera griseana Hübner) is one of the most extensively studied defoliators, where numerous tree ring-based analyses on its host (Larix decidua Mill.) have aided in identifying outbreak dynamics over the past millennia. Yet, outbreaks have been widely absent after the early 1980s, and little is known about the in situ tree physiological responses and the allocation of carbon resources during and after defoliation. In summer 2018, we tracked an ongoing larch budmoth outbreak in a well-studied larch forest in the Swiss Alps. We performed biweekly monitoring on an affected and unaffected site using a unique combination of xylogenesis observations, measurements of non-structural carbohydrates, isotopic analysis of needle assimilates and ground-based and remote-sensed leaf trait observations. The budmoth induced a defoliation that lasted 40 days and could be detected by satellite observations. Soluble sugars significantly decreased in needles and stem phloem of the defoliated trees, while starch levels remained stable in the stem and root xylem compared to the control. Carbon and oxygen isotope ratios in needle assimilates indicated that neither photosynthetic assimilation rates nor stomatal conductance was different between sites before, during and after the outbreak. Defoliated trees ceased cell wall thickening 17 days earlier than unaffected trees, showing the earliest halt of ring formation recorded from 2007 untill 2013 and causing significant thinner cell walls, particularly in the latewood. No significant differences were found for cell enlargement rates and ring width. Our study revealed that an outbreak causes a downregulation of cell wall thickening first, while no starch is mobilized or leaf physiology is adjusted to compensate for the reduced carbon source due to defoliation. Our observations suggest that affected larch trees prioritize leaf recovery and carbon storage over wood biomass development.
45
Dobbertin, Matthias, Christian Hug e Lorenz Walthert. "Waldzustand in der Schweiz: Erfassung, Entwicklung und Einflussfaktoren". Schweizerische Zeitschrift fur Forstwesen 163, n. 9 (1 settembre 2012): 331–42. http://dx.doi.org/10.3188/szf.2012.0331.
Testo completoAbstract (sommario):
Forest condition in Switzerland: assessment, development and influencing factors In the early 1980s it was feared that air pollution would cause a widespread forest decline and a reduction in forest productivity. In Switzerland as in most European countries crown defoliation and foliage discoloration were selected as the most important indicators of forest condition. The Sanasilva inventory on a systematic network of plots showed an increase in the proportion of trees with high defoliation until 1995. Since then no trend has been detected. However, large annual fluctuations were often observed following years with large-scale climatic events, such as the storms Vivian and Lothar and the heat summer of 2003. Although highly variable, neither mortality nor removal rates have shown any time trend since 1985. The annual differences in crown defoliation, mortality and tree growth are mainly related to climatic factors. In addition to the climatic conditions, nutrient availability, soil water holding capacity and to a lesser extent air pollution determine the degree of crown defoliation at a given site and for a given species. Although several studies have found a negative effect of nitrogen deposition or ozone concentrations on tree foliation, others have shown that up to now nitrogen deposition has increased tree growth on nitrogen-limited sites. It can thus be concluded that presently air pollution does not pose a direct threat to tree conditions in Switzerland. However, the assessment of crown condition alone is not a suitable tool to detect the effects of air pollution on forests. This requires more detailed measurements on long-term research sites. However, as crown condition is strongly affected by site conditions and climate, it should be further monitored, particularly with regard to the predicted climate change.
46
Krause, Cornelia, Hubert Morin e Pierre-Y. Plourde. "Juvenile growth of black spruce (Picea mariana [Mill.] BSP) stands established during endemic and epidemic attacks by spruce budworm (Choristoneura fumiferana [Clemens]) in the boreal forest of Quebec, Canada". Forestry Chronicle 85, n. 2 (1 marzo 2009): 267–76. http://dx.doi.org/10.5558/tfc85267-2.
Testo completoAbstract (sommario):
In the boreal forest of Quebec, 80% of harvested black spruce (Picea mariana [Mill.] BSP) stands regenerate naturally. In the remaining 20%, forest regeneration is ensured by planting seedlings and these plantations are expected to increase future forest yields. However, predictions of future yields using the information from very young plantations in this ecosystem may have low accuracy. To compare juvenile growth in plantations versus naturally regenerated stands, and also to evaluate the impacts of spruce budworm Choristoneura fumiferana (Clemens) defoliation periods during the juvenile phase, annual height and volume growth were calculated from measurements on nine black spruce stands. The nine sites consisted of two plantations and seven post-fire, naturally regenerated stands. Of the seven naturally regenerated sites, four were epidemic and 3 endemic. The term “epidemic” refers to stands regenerated during known spruce budworm defoliation periods. The term “endemic” refers to stands regenerated during periods without severe defoliation. For height and volume growth, 5 different methods were used and compared. The annual height and volume growth of all black spruce showed a sigmoid trend, characterized by low values in the first years after germination, followed by an exponential acceleration and finally oscillation around a horizontal asymptote. The black spruce stands established during endemic periods were more productive than those established during epidemic periods, but plantations were the most productive. Key words: black spruce, juvenile growth, plantation, post-fire stands, spruce budworm outbreak, volume, yield
47
Boschma, S. P., e J. M. Scott. "Measuring and predicting the consequences of drought for a range of perennial grasses on the Northern Tablelands of New South Wales". Australian Journal of Experimental Agriculture 40, n. 2 (2000): 285. http://dx.doi.org/10.1071/ea98014.
Testo completoAbstract (sommario):
An experiment was conducted at Armidale, New South Wales to evaluate the persistence and productivity of 6 perennial grasses under 2 defoliation severities and a range of moisture/drought conditions created using a rain-out shelter. Defoliation was either moderate or severe whilst the moisture/drought conditions imposed included a non-stressed moisture treatment, and seasonal droughts simulated as 40-percentile (40-P) and 10-percentile rainfall (10-P). The treatments were applied over 2 experimental seasons; spring–summer and summer–autumn. A range of measurements was taken including plant mortality, basal area, foliage greenness, herbage mass, growth rate and digestibility. Some of these results were then used as inputs to the GrazFeed decision support system to predict liveweight gain and wool growth rate from pastures growing under such conditions. Plant mortality of over 40% was observed in Dactylis glomerata and Lolium perenne under moderate (40-P) drought conditions during spring–summer. In contrast, under severe drought conditions (10-P), less than 20% of plants died, suggesting that, when combined with defoliation stress, a more common drought can present a greater hazard to plant persistence than a severe drought during spring–summer. Plant mortality was reduced and non-significant when subjected to the summer–autumn drought treatments. Plant growth and predictions of animal productivity varied widely among the species challenged with drought and defoliation stresses. Predicted liveweight gains of weaner sheep under severe drought conditions (10-P) varied between species ranging from 20 to 110 g/day. Under the same conditions, predicted wool growth rates varied between species from 5 to 11 g/wether. day, while pasture growth rates varied from a low of 0 to more than 120 kg DM/ha. day. The animal effects were due largely to differences in herbage mass and the degree to which the grass remained green. These results highlight the importance of maintaining the most productive species in pastures through drought.
48
Beloiu, Mirela, Reinhold Stahlmann e Carl Beierkuhnlein. "High Recovery of Saplings after Severe Drought in Temperate Deciduous Forests". Forests 11, n. 5 (13 maggio 2020): 546. http://dx.doi.org/10.3390/f11050546.
Testo completoAbstract (sommario):
Drought episodes are predicted to increase their intensity and frequency globally, which will have a particular impact on forest vitality, productivity, and species distribution. However, the impact of tree species interaction on forest vulnerability to drought is not yet clear. This study aims to assess how deciduous saplings react to drought and whether tree species diversity can buffer the impact of drought stress on tree saplings. Based on field measurements of crown defoliation and species diversity, vulnerability, drought recovery, and species interaction were analyzed. Fieldwork was carried out in Central Eastern Germany in 2018 during the vegetation season and repeated in 2019. Ten random saplings were measured in each of the 218 plots (15 × 15 m) with 2051 saplings in total out of 41 tree species. We found that 65% of the saplings experienced defoliation during the drought of 2018, of which up to 13% showed complete defoliation. At the species level, Fagus sylvatica L. and Betula pendula Roth. saplings were less affected (<55%), whereas Carpinus betulus L., Sorbus aucuparia L., and Frangula alnus Mill. saplings were the most affected (≥85%). One year later, in 2019, C. betulus and S. aucuparia had a faster recovery rate than F. sylvatica, B. pendula, Quercus spp., and Crataegus spp. (p < 0.001). Furthermore, we showed that forest stands with high sapling species diversity had a reduced vitality under drought stress (p < 0.001), indicating a higher competition for resources. The study provides evidence that F. sylvatica saplings can withstand and survive to persistent drought. Species-specific responses to drought are essential to be considered for implementing adaptive forest management strategies to mitigate the impact of climate change.
49
Looney, Caitlin, Astrid Wingler e Michael Egan. "The Impact of Herbage Mass on Perennial Ryegrass Swards in Autumn on Autumn and over Winter Production and Characteristics". Agronomy 11, n. 6 (3 giugno 2021): 1140. http://dx.doi.org/10.3390/agronomy11061140.
Testo completoAbstract (sommario):
Accumulating herbage mass to facilitate the extension of the grazing season in autumn is commonly practised. The objective of the current study was to investigate the effect of accumulating varying target herbage masses (THM) in autumn and imposing different defoliation dates (DD), on herbage mass, sward quality and water-soluble carbohydrates in autumn and the subsequent spring. A 4 × 3 factorial split plot design was assigned with four THM (Low ≈ 500 kg·DM·ha−1, Medium ≈ 1500 kg·DM·ha−1, High ≈ 2000 kg·DM·ha−1 and Very high ≈ 3000 kg·DM·ha−1) and three DD (DD1—15 October, DD2—7 November and DD3—21 November), across two years. Measurements were carried out at each DD and in spring. Differences in sward quality were found between each THM on different DD. Sward quality reduced from DD2 to DD3 in the high THM (−13 g·kg−1 DM CP, p < 0.001). The very high THM had the lowest sward quality from DD1 (206 g·kg−1 DM CP, p < 0.001 and 787 g·kg−1 DM DMD, p < 0.05). This study has identified the defoliation date of THM in autumn as key to improving autumn management strategies for increased utilisation and sward quality.
50
Prado, P., F. Tomas, T. Alcoverro e J. Romero. "Extensive direct measurements of Posidonia oceanica defoliation confirm the importance of herbivory in temperate seagrass meadows". Marine Ecology Progress Series 340 (2007): 63–71. http://dx.doi.org/10.3354/meps340063.
Testo completo