| Determination of the balance between carbon fixation and water usage in forest ecosystems is critically important for sustainable forest management and water conservation.In this dissertation,with the vegetation in a broadleaved-Korean pine forest zone of Changbai Mountain as a case study,the carbon and water balance of forest vegetation and their relationships with forest stand and environment factors were studied by combining the method of field survey,modelling,remote sensing datasets and spatial analysis,from plot level to landscape scale.The study focused on two questions:?1?what kind of relationships occur between carbon and water fluxes in forest ecosystems with stand development??2?what are the driving factors on spatiotemporal variations in landscape-scale forest carbon-water balance?The main results of the study are summarized below:?1?The stand density in 12 broadleaved-Korean pine forest plots of age sequence decreased markedly from young to middle age,and then remained stable at the later developmental stage.The diameter distribution of trees all exhibited an inverse J-shape pattern except in the youngest stand,indicating that all stands had adequate natural regeneration conditions.On the whole,species richness index,Shannon-wiener index and evenness index of the tree layer showed a unimodal curve,with peak in the middle-age forest stage and lowest values in the mature forest stage.The biomass increased by 2.56 folds from 184.27 t·hm-2 in young age to 472.14 t·hm-2 in the old age.?2?The uncertainty of simulated net primary productivity?NPP?is higher than in simulated evapotranspiration?ET?.Both NPP and ET of broad-leaved trees were generally less sensitive to ecophysiological parameters than Korean pine.Leaf carbon to nitrogen ratio?C:Nieaf?,fine root carbon to nitrogen ratio?C:Nfr?,specific leaf area?SLA?,and water interception coefficient?Wint?were among the highly sensitive parameters affecting the modeled NPP;while fine root carbon to new leaf carbon allocation?FRC:LC?,new stem carbon to new leaf carbon allocation?SC:LC?and SLA were the highly sensitive parameters influencing ET.In addition,fraction of leaf N in Rubisco,leaf and fine root turnover,ratio of all sided to projected leaf area are also critical parameters affecting the output of Biome-BGC simulations.The degree of sensitivity of the critical parameters varied with species and sites.?3?Validation using tree-ring width index?RWI?indicates that Biome-BGC well simulates the temporal NPP patterns in broadleaved-Korean pine forests.The simulated NPP matches well with MODIS NPP,but the simulated ET were somewhat underestimated compared to the MODIS ET products with a large deviation.NPP increased with age during the initial stage of forest development,reaches the peak at middle-age and followed by decline,ET showed similar trends with stand age,but did not decline as much in the old stands.Simulations of carbon and water fluxes in broadleaved-Korean pine forests of four developmental scenarios showed that values of WUE were highest in the mature stage in the two scenarios with planted Korean pine forests experiencing either natural development or controlled cutting.However,when the initial state is natural secondary birch forest experiencing either natural development or controlled cutting,WUE was highest in the young stage.?4?Over the period 2000-2014,the mean annual NPP,ET and WUE over a forest landscape was 453.8 g C·m-2·a-1,581.5 mm·a-1 and 0.79 g C·m-2·mm-1,respectively.The landscape-level NPP and WUE displayed an increasing trend,whereas ET slightly decreased.The spatial variations in NPP,ET,and WUE were commonly attributable to forest type,stand age class and density,establishment mode,and temperature variables,with some effects of other selective factors on ET and WUE.The three forest types were significantly?p<0.05?differentiated in the mean annual NPP,ET,and WUE:the coniferous forests were highest in NPP and WUE,and lowest in ET,followed by the mixed-wood forests;whereas the broadleaved forests were lowest in NPP and WUE,and highest in ET.The mean annual NPP,ET and WUE increased with stand age typically in coniferous forests,and weakly in mixed-wood forests.The natural stands had significantly?p<0.001?greater NPP and WUE than planted stands in coniferous and mixed-woods.The overall results show that forest type and stand-age class are key factors affecting carbon and water balances of the studied forest ecosystems.Facilitating the establishment of coniferous trees and conservation of mature forest stands,and near-natural management of planted forests,can be favorable options for delivering ecosystem services of carbon sequestration and water conservation in temperate regions. |
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