Estimating stand transpiration of natural forests using traditional methods through up-scaling of sap fl ux density from sample trees based on stand sapwood area only is diffi cult because of the complexity of species...Estimating stand transpiration of natural forests using traditional methods through up-scaling of sap fl ux density from sample trees based on stand sapwood area only is diffi cult because of the complexity of species,ages,and hierarchical structure of natural forests.To improve stand transpiration estimation,we developed an up-scaling method by considering the tree dominance eff ect based on the assumption that individual tree transpiration is aff ected by crown dominance and species,in addition to factors previously considered such as meteorological conditions,sapwood area,and soil moisture.In this study,the meteorological factors,soil moisture,and sap fl ux density of 15 sample trees of diff erent species and dominance in a natural evergreen and deciduous broadleaved mixed forest were simultaneously monitored from March 2012 to February 2014 in the Karst mountain region in southwestern China.After establishing a single tree transpiration model which considers the eff ects of dominance and species,an up-scaling method was explored to estimate stand transpiration.The results show that the transpiration intensity increased exponentially with increasing tree dominance.The contribution to annual stand transpiration from a few dominant trees(5.4%of trees, 28.2% of basal area) was up to 65.0%. The correspondingcontribution was 16.2% from sub-dominant trees(7.6% of trees, 16.2% of basal area) and 22.8% from middleandlower-layer trees (87.0% of trees, 55.6% of basal area).The variation of individual tree transpiration was mainly(97.9%) explained by tree dominance, but very weakly bytree species. The estimated annual stand transpiration was300.2 mm when using the newly developed method whichconsiders tree dominance, 52.5 mm (14.9%) lower than theestimation (352.7 mm) of traditional method which considersonly the sapwood area eff ect, and 8.5 mm (2.7%) lowerthan the estimation (308.6 mm) which considers the eff ectsof both species composition and sapwood area. The maintree characteristics aff ecting stand transpiration are tree size(sapwood area) and dominance. Consideration of tree dominancewill signifi cantly improve stand transpiration estimationand provide a more solid basis for guiding integratedforest-water management at stand scale.展开更多
文摘Estimating stand transpiration of natural forests using traditional methods through up-scaling of sap fl ux density from sample trees based on stand sapwood area only is diffi cult because of the complexity of species,ages,and hierarchical structure of natural forests.To improve stand transpiration estimation,we developed an up-scaling method by considering the tree dominance eff ect based on the assumption that individual tree transpiration is aff ected by crown dominance and species,in addition to factors previously considered such as meteorological conditions,sapwood area,and soil moisture.In this study,the meteorological factors,soil moisture,and sap fl ux density of 15 sample trees of diff erent species and dominance in a natural evergreen and deciduous broadleaved mixed forest were simultaneously monitored from March 2012 to February 2014 in the Karst mountain region in southwestern China.After establishing a single tree transpiration model which considers the eff ects of dominance and species,an up-scaling method was explored to estimate stand transpiration.The results show that the transpiration intensity increased exponentially with increasing tree dominance.The contribution to annual stand transpiration from a few dominant trees(5.4%of trees, 28.2% of basal area) was up to 65.0%. The correspondingcontribution was 16.2% from sub-dominant trees(7.6% of trees, 16.2% of basal area) and 22.8% from middleandlower-layer trees (87.0% of trees, 55.6% of basal area).The variation of individual tree transpiration was mainly(97.9%) explained by tree dominance, but very weakly bytree species. The estimated annual stand transpiration was300.2 mm when using the newly developed method whichconsiders tree dominance, 52.5 mm (14.9%) lower than theestimation (352.7 mm) of traditional method which considersonly the sapwood area eff ect, and 8.5 mm (2.7%) lowerthan the estimation (308.6 mm) which considers the eff ectsof both species composition and sapwood area. The maintree characteristics aff ecting stand transpiration are tree size(sapwood area) and dominance. Consideration of tree dominancewill signifi cantly improve stand transpiration estimationand provide a more solid basis for guiding integratedforest-water management at stand scale.
