The determination of natural variation in physical habitat conditions and the establishment of least-disturbed reference standards is important for ecosystem conservation.Tropical regions hold most of the global fresh...The determination of natural variation in physical habitat conditions and the establishment of least-disturbed reference standards is important for ecosystem conservation.Tropical regions hold most of the global freshwater diversity,nevertheless little is known about the natural conditions of their physical habitats.We calculated 255 physical habitat metrics for 31 stream sites in five protected areas of the Brazilian S~ao Francisco River basin to identify the most variable characteristics among tropical streams in least-disturbed areas.We performed principal components analyses(PCA)to find the most relevant metrics for ordination of streams in the following categories:water quality(2);substrate(7);fish shelter(6);riparian vegetation(9);and channel morphology(7).We used distance-based linear models(DISTLM)to test how much of the variation of these metrics could be explained by geographic position,average elevation,and average discharge of stream sites.The best statistically significant models explained 42%of substrate(33%geographic position;9%average elevation),26%of channel morphology(22%geographic position;4%average discharge),23%of water quality(14%geographic position;9%average discharge),17%of fish shelter(9%geographic position;8%average elevation),and 14%of riparian vegetation(7%geographic position;7%average elevation)variation.Thus,regional features(e.g.geology and climate)related to the geographic position are of greatest importance,followed by average elevation and discharge for determining physical habitat characteristics.Therefore,we suggest that reference sites should be set for tropical streams in the same regional landscape and with similar average elevation and discharge.展开更多
Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to ...Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to dry land degradation in the southwestern United States is reported.The local NPP scaling(LNS)approach was applied to map the extent and magnitude of degrada tion.LNS seeks to identifty reference sites in which there is no degradation that can be used as a standard for comparison with other sites that share the same environment,except for degradation.Twelve years were analyzed(2000--2011),using Normalized Difference Vegetation Index(NDVI)data(250 m)from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite-borne multispectral sensor.The results indicated that the total NPP reductions in the study area were about35.9±4.7Tg C/yr,which equates to 0.31±0.04 Mg C·ha^(-1)· yr^(-1).The NPP reductions in grassland-savanna and livestock grazing areas were large and mostly consistent between years in spite of large variations in overall NPP caused by differences in land-use,interannual variations in rainfall,and other aspects of weather.In comparison with other cover types,forested land generally had higher NPP reduction per unit area.The maps also enable attribution of degradation from the finest management units to entire agencies,such as the Bureau of Land Management,which had 50%less production per unit area than the U.S.Forest Service.The degradation within Native American land was low with total NPP reduction of about 2.41±0.24 Tg C/yr and unit area reduction of productivity of just 0.21±0.02 Mg C·ha^(-1)·yr^(-1),yet the percent reduction from potential was in equivalence with other land management agencies.展开更多
基金Fundaçao Grupo Boticario deProteçao a NaturezaConselho Nacional de Desenvolvimento Científico e Tecnologico,Grant/Award Number:CNPq No.303548/2017-7Coordenaçao de Aperfeiçoamento de Pessoal de Nível Superior.
文摘The determination of natural variation in physical habitat conditions and the establishment of least-disturbed reference standards is important for ecosystem conservation.Tropical regions hold most of the global freshwater diversity,nevertheless little is known about the natural conditions of their physical habitats.We calculated 255 physical habitat metrics for 31 stream sites in five protected areas of the Brazilian S~ao Francisco River basin to identify the most variable characteristics among tropical streams in least-disturbed areas.We performed principal components analyses(PCA)to find the most relevant metrics for ordination of streams in the following categories:water quality(2);substrate(7);fish shelter(6);riparian vegetation(9);and channel morphology(7).We used distance-based linear models(DISTLM)to test how much of the variation of these metrics could be explained by geographic position,average elevation,and average discharge of stream sites.The best statistically significant models explained 42%of substrate(33%geographic position;9%average elevation),26%of channel morphology(22%geographic position;4%average discharge),23%of water quality(14%geographic position;9%average discharge),17%of fish shelter(9%geographic position;8%average elevation),and 14%of riparian vegetation(7%geographic position;7%average elevation)variation.Thus,regional features(e.g.geology and climate)related to the geographic position are of greatest importance,followed by average elevation and discharge for determining physical habitat characteristics.Therefore,we suggest that reference sites should be set for tropical streams in the same regional landscape and with similar average elevation and discharge.
文摘Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to dry land degradation in the southwestern United States is reported.The local NPP scaling(LNS)approach was applied to map the extent and magnitude of degrada tion.LNS seeks to identifty reference sites in which there is no degradation that can be used as a standard for comparison with other sites that share the same environment,except for degradation.Twelve years were analyzed(2000--2011),using Normalized Difference Vegetation Index(NDVI)data(250 m)from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite-borne multispectral sensor.The results indicated that the total NPP reductions in the study area were about35.9±4.7Tg C/yr,which equates to 0.31±0.04 Mg C·ha^(-1)· yr^(-1).The NPP reductions in grassland-savanna and livestock grazing areas were large and mostly consistent between years in spite of large variations in overall NPP caused by differences in land-use,interannual variations in rainfall,and other aspects of weather.In comparison with other cover types,forested land generally had higher NPP reduction per unit area.The maps also enable attribution of degradation from the finest management units to entire agencies,such as the Bureau of Land Management,which had 50%less production per unit area than the U.S.Forest Service.The degradation within Native American land was low with total NPP reduction of about 2.41±0.24 Tg C/yr and unit area reduction of productivity of just 0.21±0.02 Mg C·ha^(-1)·yr^(-1),yet the percent reduction from potential was in equivalence with other land management agencies.
