Modeling the topographic influence on aboveground biomass using a coupled model of hillslope hydrology and ecosystem dynamics

[摘要] Topographic heterogeneity and lateral subsurface flow at thehillslope scale of ≤1  km may have outsized impacts on tropical forestthrough their impacts on water available to plants under water-stressed conditions. However, vegetation dynamics and finer-scale hydrologicprocesses are not concurrently represented in Earth system models. In thisstudy, we integrate the Energy Exascale Earth System Model (E3SM) land model (ELM) that includes the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), with a three-dimensional hydrology model (ParFlow) toexplicitly resolve hillslope topography and subsurface flow and performnumerical experiments to understand how hillslope-scale hydrologic processes modulate vegetation along water availability gradients at Barro ColoradoIsland (BCI), Panama. Our simulations show that groundwater table depth(WTD) can play a large role in governing aboveground biomass (AGB) whendrought-induced tree mortality is triggered by hydraulic failure. Analyzingthe simulations using random forest (RF) models, we find that thedomain-wide simulated AGB and WTD can be well predicted by statictopographic attributes, including surface elevation, slope, and convexity, and adding soil moisture or groundwater table depth as predictors furtherimproves the RF models. Different model representations of mortality due tohydraulic failure can change the dominant topographic driver for thesimulated AGB. Contrary to the simulations, the observed AGB in thewell-drained 50 ha forest census plot within BCI cannot be well predicted bythe RF models using topographic attributes and observed soil moisture aspredictors, suggesting other factors such as nutrient status may have a larger influence on the observed AGB. The new coupled model may be useful forunderstanding the diverse impact of local heterogeneity by isolating thewater availability and nutrient availability from the other external andinternal factors in ecosystem modeling.

[学科分类] 土木及结构工程学