Construction And Application Of Biomass Equations Of Mixed Tree Species In Northeast Temperate Forests

Biomass is the basic characteristic of ecosystem,and the foundation of understanding global climate change and carbon cycle.The most commonly method of estimating biomass is to establish biomass equations by using allometric relationship.However,the limit of narrow DBH range and tree species constrained the practical application of biomass equations,and made it difficult to estimate large-scale biomass accurately.In this study,the biomass equations for subcanopy tree species were developed based on 6 subcanopy species in natural decondary forest of Maoershan;the biomass equations of large DBH range were developed based on 41tree species which were divided into four tree species groups,and quantified the errors of the published biomass equations caused by DBH extrapolation.The main results are as follows:(1)Using destructively sampled data of six common subcanopy species(Syringa reticulate var.amurensis,Padus racemosa,Acer ginnala,Malus baccata,Rhamnus davurica,and Maackia amurensis)established biomass equations in a temperate forest of Northeast China.The mixed-species and species-specific biomass allometric equations were well fitted against diameter at breast height(DBH).Adding tree height(H)as the second predictor increased the R~2of the models compared with the DBH-only models by–1%to+3%.The R~2of DBH-only and DBH-H equations for the total biomass of mixed-species were 0.985 and 0.986,respectively.On average,the biomass allocation proportions for the six species were in the order of stem(45.5%)>branch(30.1%)>belowground(19.5%)>foliage(4.9%),with a mean root:shoot ratio of 0.24.Biomass allocation to each specific component differed among species,which affected the performance of the mixed-species model for particular biomass component.When estimating the biomass of subcanopy species using the equations for canopy species(e.g.,Betula platyphylla,Ulmus davidiana var.japonica,and Acer pictum subsp.mono),the errors in individual biomass estimation increased with tree size(up to 68.8%at 30 cm DBH),and the errors in stand biomass estimation(up to 19.2%)increased with increasing percentage of basal area shared by subcanopy species.The errors caused by selecting such inappropriate models could be removed by multiplying adjustment factors,which were usually power functions of DBH for biomass components.In practical application,the DBH-only biomass equations can content the requirement of subcanopy biomass estimation in general.(2)Using destructively sampled data of 41 species with large range of DBH(up to 78.8cm)were used to establish the biomass equations of mixed tree species groups and single tree species group in a broad-leaved Korean pine forest,which were divided into four tree species groups:broad-leaved canopy species group,coniferous canopy species group,broad-leaved subcannopy species group,and coniferous subcanopy species group.In general,the R~2of mixed species groups were higher than that of single species group.the R~2of DBH-only biomass equations were lower than that of DBH-H biomass equations,and the regression of adding wood density(WD)biomass equation were improved.The published biomass equations in Northeast China were verified by the measured values.Because most of the measured DBH exceeded the range of modeling DBH,there were great differences between different equations.It should be cautious to select the model used to estimate the biomass of large DBH trees in the published biomass equations.In practical application,when estimating the biomass of large DBH trees,it is recommended to select the meta-analysis biomass equations or mixed species biomass equation with the large DBH range,which can provide a wider range of DBH biomass estimation.In addition,the use of volume or multiplying the adjustment factors to calibrate the biomass,are available methods to reduce the error of large DBH trees biomass estimations.In this paper,we developed biomass equations for common subcanopy species for secondary forests in northeast China,expanded the DBH range and tree species of large tree biomass equations,and compared the differences between the published biomass equations in Northeast China,quantified the errors of biomass estimation in DBH extrapolation.These results provide methodological support for accurate biomass estimation,which can help to improve estimates of forest biomass and carbon stocks.