Driving Factors Of The Distribution Patterns Of Karst Forest Aboveground Biomass In Maolan

Aboveground biomass in forests is the most dynamic carbon reservoir in forest ecosystems and the most basic characteristic data of forest ecosystems,and forests,as the largest terrestrial ecosystems,play an important role in energy flow,material cycle and carbon cycle.In the karst landforms of southwest China,there is a typical non-zonal forest,called karst forest,which plays an important role in maintaining environmental stability in southwest China.However,the ecosystem is less stable,less resilient and self-resilient,and vulnerable to disturbance and destruction.Understandings of the distribution patterns and driving factors of forest above-ground biomass facilitate the evaluation of forest ecosystem functioning,and provides support for karst forest management.Here,in the karst forests of Maolan National Nature Reserve,sampling forest plots were established,and the aboveground biomass of forest woody plants were estimated by allometric equations,to examine the distribution patterns of karst forest above-ground biomass.Also,the environmental conditions of the sample plots were measured,and their effects on the distribution patterns of forest above-ground biomasses were investigated.The findings are as below:(1)By adopting statistical methods such as the t-test,the pattern of above-ground biomass distribution between forest stratum(i.e.,overstory or understory),leaf habit plant groups(i.e.,evergreen or deciduous)and species,were assessed.The results showed that the above-ground biomass of the overstory stratum was larger than that of the understory stratum.The aboveground biomass of evergreen plants was larger than that of the deciduous plants.Further,the difference of aboveground biomass of different leaf habits was most pronounced in the understory stratum.A small number of species contributed the majority of above-ground biomass,both for the community and each forest stratum,the first ten species in rank accounted for more than 50% of total above-ground biomass.(2)By adopting statistical methods such as the linear mixed-effects model and model selection,I found the above-ground biomass of the community and of different stratum were driven by both the abiotic and biotic factors.For abiotic factors,the above-ground biomass of community and different stratum differed between topographic habitats.Specifically,above-ground biomass of the community and of upper stratum in the piedmont were the largest among the three topopgrahic habitats,whereas biomass of the lower stratum peaked at the hilltop.For biotic factors,the above-ground biomass of the community was positively affected by variation in diamater at breast height(DBH)and Baker-Parker dominance index,and was negatively affected by rock-exposure rate.For different stratum,I found that the above-ground biomass of overstory stratum and understory stratum both were positively affected by stem density,variation of DBH,and Baker-Parker dominance index.(3)By adopting statistical methods such as the linear mixed-effects model,I analyzed the driving factors of the above-ground biomass of the different leaf habit plants.I found the evergreen plants and deciduous plants were negatively affected by rock-exposure rate.I also found that the above-ground biomass of both leaf habit plant groups varied with topographic habitat,shown as the above-ground biomass in the piedmont were larger than at the hilltop and slope.Further,soil depth showed a positive effect on above-ground biomass of evergreen plants.At the species level,I found the driving factors of above-ground biomass differed between species.For example,the aboveground biomass of Cyclobalanopsis glauca,Platycarya longipes and Lindera communis all varied with topographic habitat,whereas only Cyclobalanopsis glauca and Lindera communis showed response to the change of rock-exposure rate,and only Platycarya longipes responded to the change of slope.The findings imply that both the abiotic and biotic factors work together in regulating the above-ground biomass of woody plants in Maolan karst forests,and differences exist between forest stata,leaf habit group,and species identity,in response to these drivers.This study deepens our understandings of the distribution patterns and driving factors of above-ground biomass of karst forest,and points to the insights gained from investigating forest biomass simultaneously from multiple angles.In addition,this study provides intellectual support for the management of Maolan karst forests.