I5.6 ELM-FATES high latitude and shifts in forest cover

Abstract

Changes in high-latitude forests have strong implications to regional and global climate, and water and carbon cycling. Shifts in canopy cover (i.e., abundance and shifts between evergreen and deciduous species) will alter albedo, carbon, and water fluxes. For example, many studies suggest that increasing fire frequency will shift conifer-dominated forests to deciduous forests. Deciduous trees transpire 21–25% of available snowmelt water, while coniferous trees transpire <1%. A shift to deciduous trees therefore reduces groundwater recharge, and potentially leads to more storms and lightning-induced fires. All these climate-related interactions will affect plant competition, survival, and ultimately community distribution and carbon storage. To be able to accurately predict and model these complex ecological processes we are using a new dynamic vegetation model (FATES; Functionally-Assembled Terrestrial Ecosystem Simulator) that is coupled to ELMv1, the land surface model in E3SM. We use FATES to quantify the impacts on water cycling (e.g., water use efficiency, latent heat, soil water storage) and carbon fluxes (NEE) under transitions between boreal evergreen and deciduous trees.

To evaluate changes in high-latitude water and carbon cycling as a result of climate-vegetation interactions, we performed a parameter sensitivity analysis using a Latin hypercube approach to sample the parameter space of 15 main vegetation parameters, over a 100-member ensemble run. In addition, leaf and wood allometry parameters for boreal plants have been updated based on observational data from the BAAD Database. Initial tests of FATES at a boreal Alaska site found strong biomass sensitivity to soil moisture stress. Therefore, we will apply the newly developed plant hydraulic scheme (FATES-Hydro) which will allow us to simulate the impacts of precipitation and soil moisture changes on shifting boreal evergreen and deciduous tree cover.