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
Soil water content(SWC)and meteorological conditions,as key environmental variables influencing tree water use,vary highly within the growing season,hindering a better understanding of environmental control mechanisms...Soil water content(SWC)and meteorological conditions,as key environmental variables influencing tree water use,vary highly within the growing season,hindering a better understanding of environmental control mechanisms on canopy transpiration(Ec).Disentangling the effects of these variables on Ec across growing-season stages is crucial for Ec estimation and forest management.In this study,43-year-old Pinus tabuliformis Carr.and 31-yearold Platycladus orientalis(L.)Franco plantations in the semiarid Chinese Loess Plateau were monitored for Ec during the growing season of 2015-2020.The contributions of environmental factors to Ec were assessed using the boosted regression tree(BRT)model.Results showed that the contributions of SWC to Ec were greater at the early(May-June)and late(September)stages,while the contributions of vapor pressure deficit(VPD)and total solar radiation(Rs)to Ec increased at the middle(July-August)stage due to high soil water availability.Overall,Ec in both plantations was dominated by SWC(20.4%≤contributions≤48.8%)and Rs(22.7%≤contributions≤35.8%).Both species exhibited strong stomatal regulation of Ec.Specifically,stomatal opening was significantly inhibited by VPD at the early stage and strongly affected by SWC at the late stage.This study highlights that soil water conditions in artificial forests should be adjusted according to changes in influencing factors on Ec.Particularly during the early and late stages,measures(e.g.,land preparation,thinning,and pruning)can be implemented to improve soil moisture in such dryland forests.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.
基金supported by the National Key Research&Development Project of China(No.2022YFF1300403)the National Natural Science Foundation of China(Nos.U21A2011,41971129,and 32401663)the Open Fund of the State Key Laboratory of Loess Science(No.SKLLQG2423).
文摘Soil water content(SWC)and meteorological conditions,as key environmental variables influencing tree water use,vary highly within the growing season,hindering a better understanding of environmental control mechanisms on canopy transpiration(Ec).Disentangling the effects of these variables on Ec across growing-season stages is crucial for Ec estimation and forest management.In this study,43-year-old Pinus tabuliformis Carr.and 31-yearold Platycladus orientalis(L.)Franco plantations in the semiarid Chinese Loess Plateau were monitored for Ec during the growing season of 2015-2020.The contributions of environmental factors to Ec were assessed using the boosted regression tree(BRT)model.Results showed that the contributions of SWC to Ec were greater at the early(May-June)and late(September)stages,while the contributions of vapor pressure deficit(VPD)and total solar radiation(Rs)to Ec increased at the middle(July-August)stage due to high soil water availability.Overall,Ec in both plantations was dominated by SWC(20.4%≤contributions≤48.8%)and Rs(22.7%≤contributions≤35.8%).Both species exhibited strong stomatal regulation of Ec.Specifically,stomatal opening was significantly inhibited by VPD at the early stage and strongly affected by SWC at the late stage.This study highlights that soil water conditions in artificial forests should be adjusted according to changes in influencing factors on Ec.Particularly during the early and late stages,measures(e.g.,land preparation,thinning,and pruning)can be implemented to improve soil moisture in such dryland forests.
