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61.
62.
Marlen D. Eve Kris M. Havstadt Walter G. Whitford Marlen D. Eve 《Environmental monitoring and assessment》1999,54(3):205-227
Considerable evidence documents that certain changes in vegetation and soils result in irreversibly degraded rangeland ecosystems. We used Advanced Very High Resolution Radiometer (AVHRR) imagery to develop calibration patterns of change in the Normalized Difference Vegetation Index (NDVI) over the growing season for selected sites for which we had ground data and historical data characterizing these sites as irreversibly degraded. We used the NDVI curves for these training sites to classify and map the irreversibly degraded rangelands in southern New Mexico. We composited images into four year blocks: 1988–1991, 1989–1992, and 1990–1993. The overlap in pixels classified as irreversibly degraded ranged from 42.6% to 84.3% in year block comparisons. Quantitative data on vegetation composition and cover were collected at 13 sites within a small portion of the study area. Wide coverage reconnaissance of boundaries between vegetation types was also conducted for comparisons with year block maps. The year block 1988–1991 provided the most accurate delineation of degraded areas. The rangelands of southern New Mexico experienced above average precipitation from 1990–1993. The above average precipitation resulted in spatially variable productivity of ephemeral weedy plants on the training sites and degraded rangelands which resulted in much smaller areas classified as irreversibly degraded. We selected imagery for a single year, 1989, which was characterized by the absence of spring annual plant production in order to eliminate the confounding effect of reflectance from annual weeds. That image analysis classified more than 20% of the rangelands as irreversibly degraded because areas with shrub-grass mosaic were included in the degraded classification. The single year image included more than double the area classified as irreversibly degraded by the year blocks. AVHRR imagery can be used to make triage assessments of irreversibly degraded rangeland but such assessment requires understanding productivity patterns and variability across the landscapes of the region and careful selection of the years from which imagery is chosen. 相似文献
63.
Kris Verheyen Margot Vanhellemont Harald Auge Lander Baeten Christopher Baraloto Nadia Barsoum Simon Bilodeau-Gauthier Helge Bruelheide Bastien Castagneyrol Douglas Godbold Josephine Haase Andy Hector Hervé Jactel Julia Koricheva Michel Loreau Simone Mereu Christian Messier Bart Muys Philippe Nolet Alain Paquette John Parker Mike Perring Quentin Ponette Catherine Potvin Peter Reich Andy Smith Martin Weih Michael Scherer-Lorenzen 《Ambio》2016,45(1):29-41
64.
Wuytack T Wuyts K Van Dongen S Baeten L Kardel F Verheyen K Samson R 《Environmental pollution (Barking, Essex : 1987)》2011,159(10):2405-2411
We aimed at evaluating the effect of low-level air pollution on leaf area fluctuating asymmetry (FAA) and specific leaf area (SLA) of Salix alba L., taking into account other environmental factors. Cuttings were grown in standardized conditions in the near vicinity of air quality measuring stations in Belgium. Variability of SLA and FAA between measuring stations explained 83% and 7.26%, respectively, of the total variability. FAA was not influenced by air pollution or environmental factors such as shading, herbivory, air temperature and humidity. SLA was increased by an increase in shadow, while NOx and O3 concentrations had only a marginal influence. The influence of SO2 concentration was negligible. Although our data analysis suggests a relationship between SLA and NOx/O3 concentration, the absence of a straightforward relationship between FAA and SLA and air pollution still questions the usefulness of these bio-indicators for monitoring air pollution. 相似文献
65.
Water utilities that rely on surface water may be vulnerable to future droughts and floods, a vulnerability that may be magnified by climate perturbations as well as shorter-term and, in some cases, ongoing changes in the political and regulatory environment in which utilities operate. Unfortunately, day-to-day responsibilities currently occupy most utility operators, leaving little time to plan for inherently uncertain effects. The record of actual responses to past droughts and floods can be illuminating, however, particularly when placed in the context of plausible hydrologic disruption and pressures such as population growth, floodplain development and new regulatory demands. This paper draws on interviews with water utility operators in the northwestern USA to highlight opportunities and constraints that water utilities may face vis-à-vis such disruptions. Key considerations affecting vulnerabilities include water rights, institutional barriers to efficient utility operations, hazard management policy and the fiscal status of utilities. 相似文献
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Fundamental to the accuracy of stable isotope analysis in trophodynamic studies is the ability to predict discrimination between
a consumer and its diet. Despite the widespread use of stable isotope analysis in trophic ecology, uncertainty still surrounds
the factors affecting consumer-diet discrimination. Here we present evidence that diet quality and location of muscle tissue
analysed affects the consumer-diet discrimination for the western rock lobster, Panulirus cygnus. Consumer-diet δ15N and δ13C discrimination for western rock lobster tail tissue were 1.67–2.97 and 2.92–3.60‰, respectively, with δ13C discrimination differing to values reported in the literature. Differences in nitrogen and carbon discrimination were observed
between tail and leg tissue of lobsters of 1.22 and 1.13‰, respectively. Diet quality was also found to affect consumer-diet
discrimination, with high protein pilchard diet leading to lower δ15N and higher δ13C discrimination. Diet quality should be considered as a factor that has the potential to affect consumer-diet discrimination
when interpreting results from stable isotope studies. 相似文献
69.
Effects of Stocking Rate on the Variability of Peak Standing Crop in a Desert Steppe of Eurasia Grassland 总被引:1,自引:0,他引:1
Zhongwu Wang Shuying Jiao Guodong Han Mengli Zhao Haijun Ding Xinjie Zhang Xiaoliang Wang Eldon L. Ayers Walter D. Willms Kris Havsatad Lata A Yongzhi Liu 《Environmental management》2014,53(2):266-273
Proper grazing management practices can generate corresponding compensatory effects on plant community production, which may reduce inter-annual variability of productivity in some grassland ecosystems. However, it remains unclear how grazing influences plant community attributes and the variability of standing crop. We examined the effects of sheep grazing at four stocking rate treatments [control, 0 sheep ha?1 month?1; light (LG), 0.15 sheep ha?1 month?1; moderate (MG), 0.30 sheep ha?1 month?1; and heavy (HG), 0.45 sheep ha?1 month?1] on standing crop at the community level and partitioned by species and functional groups, in the desert steppe of Inner Mongolia, China. The treatments were arranged in a completely randomized block design over a 9-year period. Standing crop was measured every August from 2004 to 2012. Peak standing crop decreased (P < 0.05) with increasing stocking rate; peak standing crop in the HG treatment decreased 40 % compared to the control. May–July precipitation explained at least 76 % of the variation in peak standing crop. MG and HG treatments resulted in a decrease (P < 0.05) in shrubs, semi-shrubs, and perennials forbs, and an increase (P < 0.05) in perennial bunchgrasses compared to the control. The coefficients of variation at plant functional group and species level in the LG and MG treatments were lower (P < 0.05) than in the control and HG treatments. Peak standing crop variability of the control and HG community were greatest, which suggested that LG and MG have greater ecosystem stability. 相似文献
70.
Soil properties are well known to affect vegetation, but the role of soil heterogeneity in the patterning of vegetation dynamics is poorly documented. We asked whether the location of an ecotone separating grass-dominated and sparsely vegetated areas reflected only historical variation in degradation or was related to variation in inherent soil properties. We then asked whether changes in the cover and spatial organization of vegetated and bare patches assessed using repeat aerial photography reflected self-organizing dynamics unrelated to soil variation or the stable patterning of soil variation. We found that the present-day ecotone was related to a shift from more weakly to more strongly developed soils. Parts of the ecotone were stable over a 60-year period, but shifts between bare and vegetated states, as well as persistently vegetated and bare states, occurred largely in small (<40 m2) patches throughout the study area. The probability that patches were presently vegetated or bare, as well as the probability that vegetation persisted and/or established over the 60-year period, was negatively related to surface calcium carbonate and positively related to subsurface clay content. Thus, only a fraction of the landscape was susceptible to vegetation change, and the sparsely vegetated area probably featured a higher frequency of susceptible soil patches. Patch dynamics and self-organizing processes can be constrained by subtle (and often unrecognized) soil heterogeneity. 相似文献