Critical Height Sampling(CHS)estimates stand volume free from any model and tree form assumptions.Despite its introduction more than four decades ago,CHS has not been widely applied in the field due to perceived chall...Critical Height Sampling(CHS)estimates stand volume free from any model and tree form assumptions.Despite its introduction more than four decades ago,CHS has not been widely applied in the field due to perceived challenges in measurement.The objectives of this study were to compare estimated stand volume between CHS and sampling methods that used volume or taper models,the equivalence of the sampling methods,and their relative efficiency.We established 65 field plots in planted forests of two coniferous tree species.We estimated stand volume for a range of Basal Area Factors(BAFs).Results showed that CHS produced the most similar mean stand volume across BAFs and tree species with maximum differences between BAFs of 5-18m^(3)·ha^(−1).Horizontal Point Sampling(HPS)using volume models produced very large variability in mean stand volume across BAFs with the differences up to 126m^(3)·ha^(−1).However,CHS was less precise and less efficient than HPS.Furthermore,none of the sampling methods were statistically interchangeable with CHS at an allowable tolerance of≤55m^(3)·ha^(−1).About 72%of critical height measurements were below crown base indicating that critical height was more accessible to measurement than expected.Our study suggests that the consistency in the mean estimates of CHS is a major advantage when planning a forest inventory.When checking against CHS,results hint that HPS estimates might contain potential model bias.These strengths of CHS could outweigh its lower precision.Our study also implies serious implications in financial terms when choosing a sampling method.Lastly,CHS could potentially benefit forest management as an alternate option of estimating stand volume when volume or taper models are lacking or are not reliable.展开更多
Soil erosion is one of the most severe global environmental problems,and soil erosion surveys are the scientific basis for planning soil conservation and ecological development.To improve soil erosion sampling survey ...Soil erosion is one of the most severe global environmental problems,and soil erosion surveys are the scientific basis for planning soil conservation and ecological development.To improve soil erosion sampling survey methods and accurately and rapidly estimate the actual rates of soil erosion,a Pan-Third Pole region was taken as an example to study a methodology of soil erosion sampling survey based on high-spatial-resolution remote sensing images.The sampling units were designed using a stratified variable probability systematic sampling method.The spatiotemporal characteristics of soil erosion and conservation were taken into account,and finer-resolution freely available and accessible images in Google Earth were used.Through the visual interpretation of the free high-resolution remote sensing images,detailed information on land use and soil conservation measures was obtained.Then,combined with the regional soil erosion factor data products,such as rainfall-runoff erosivity factor(R),soil erodibility factor(K),and slope length and steepness factor(LS),the soil loss rates of some sampling units were calculated.The results show that,based on these high-resolution remote sensing images,the land use and soil conservation measures of the sampling units can be quickly and accurately extracted.The interpretation accuracy in 4 typical cross sections was more than 80%,and sampling accuracy,described by histogram similarity in 11 large sampling sites,show that the landuse of sampling uints can represent the structural characteristics of regional land use.Based on the interpretation of data from the sample survey and the regional soil erosion factor data products,the calculation of the soil erosion rate can be completed quickly.The calculation results can reflect the actual conditions of soil erosion better than the potential soil erosion rates calculated by using the coarse-resolution remote sensing method.展开更多
文摘Critical Height Sampling(CHS)estimates stand volume free from any model and tree form assumptions.Despite its introduction more than four decades ago,CHS has not been widely applied in the field due to perceived challenges in measurement.The objectives of this study were to compare estimated stand volume between CHS and sampling methods that used volume or taper models,the equivalence of the sampling methods,and their relative efficiency.We established 65 field plots in planted forests of two coniferous tree species.We estimated stand volume for a range of Basal Area Factors(BAFs).Results showed that CHS produced the most similar mean stand volume across BAFs and tree species with maximum differences between BAFs of 5-18m^(3)·ha^(−1).Horizontal Point Sampling(HPS)using volume models produced very large variability in mean stand volume across BAFs with the differences up to 126m^(3)·ha^(−1).However,CHS was less precise and less efficient than HPS.Furthermore,none of the sampling methods were statistically interchangeable with CHS at an allowable tolerance of≤55m^(3)·ha^(−1).About 72%of critical height measurements were below crown base indicating that critical height was more accessible to measurement than expected.Our study suggests that the consistency in the mean estimates of CHS is a major advantage when planning a forest inventory.When checking against CHS,results hint that HPS estimates might contain potential model bias.These strengths of CHS could outweigh its lower precision.Our study also implies serious implications in financial terms when choosing a sampling method.Lastly,CHS could potentially benefit forest management as an alternate option of estimating stand volume when volume or taper models are lacking or are not reliable.
基金the Strategic Priority Research Program of Chinese Academy of Sciences,Grant No.XDA20040202.
文摘Soil erosion is one of the most severe global environmental problems,and soil erosion surveys are the scientific basis for planning soil conservation and ecological development.To improve soil erosion sampling survey methods and accurately and rapidly estimate the actual rates of soil erosion,a Pan-Third Pole region was taken as an example to study a methodology of soil erosion sampling survey based on high-spatial-resolution remote sensing images.The sampling units were designed using a stratified variable probability systematic sampling method.The spatiotemporal characteristics of soil erosion and conservation were taken into account,and finer-resolution freely available and accessible images in Google Earth were used.Through the visual interpretation of the free high-resolution remote sensing images,detailed information on land use and soil conservation measures was obtained.Then,combined with the regional soil erosion factor data products,such as rainfall-runoff erosivity factor(R),soil erodibility factor(K),and slope length and steepness factor(LS),the soil loss rates of some sampling units were calculated.The results show that,based on these high-resolution remote sensing images,the land use and soil conservation measures of the sampling units can be quickly and accurately extracted.The interpretation accuracy in 4 typical cross sections was more than 80%,and sampling accuracy,described by histogram similarity in 11 large sampling sites,show that the landuse of sampling uints can represent the structural characteristics of regional land use.Based on the interpretation of data from the sample survey and the regional soil erosion factor data products,the calculation of the soil erosion rate can be completed quickly.The calculation results can reflect the actual conditions of soil erosion better than the potential soil erosion rates calculated by using the coarse-resolution remote sensing method.
