Linking Heterogeneity of Above-Ground and Subsurface Processes at the Gap-Canopy Patch Scales to Ecosystem Level Dynamics

Project Overview
Project Abstract: 
<p>Trees control soil moisture by drawing water through the roots and transpiring them to the air. They also lead to an opposite effect of reducing evaporation from the soil to the air by shading the ground and reducing the wind speed near the surface. Current watershed models simulate soil moisture at regional scales (tens to hundreds of km) and use extremely simplified representations of the interactions between vegetation and soil moisture. The differences between individual crowns and the effects of the canopy structure are not represented in these models. This project aims to improve our understanding of the relationships between evaporation, transpiration and soil moisture in heterogeneous forest canopies, and how these relationships affect soil moisture heterogeneity from the tree scale to the ecosystem and regional scales.</p><p>A combination of detailed observations and state-of-the-art high-resolution modeling tools will be used. A modeling system will be developed, which will include two models: (1) a canopy-resolving atmospheric large eddy simulation (RAFLES) to simulate the wind, humidity and temperature of the air at a resolution smaller than individual tree crowns. This model will also simulate the transpiration of individual trees; and (2) a physically-based watershed hydrology model (tRIBS-VEGGIE), also capable of operating at a resolution of a few meters. Novel radar-based volumetric observation of soil moisture, and in and above canopy micrometeorological measurements will be used to evaluate the models results.</p><p>The project will capitalize on the existing wealth of data and on-going diverse observations at the University of Michigan Biological Station (UMBS). Specifically, the coupled modeling system will be used to simulate two forest patches within the experimental and control plots of the Forest Accelerated Succession ExperimenT (FASET), a DOE-NICER funded study, in which manipulations of the canopy structure simulate a shift from mid- to late-successional tree community. The proposed project will lead to new understanding of how the small-scale structure of forests affects the atmosphere and soil moisture heterogeneity at larger scales, which will advance our capability to predict the effects of ecosystem structure at multiple scales on the exchanges of energy water and CO2 with the atmosphere, and on the functioning of the regional watershed. Such advancement is particularly important in conditions of changing climate and increased human disturbance to forests, which are expected to increase the spatial heterogeneity of forests and other important natural resources. Furthermore, the study will upscale, for the first time, a mechanistic model of fine-scale (few meters) canopy-structure to a regional scale (few km), using a hydrological model capable of resolving vegetation and topography in heterogeneous domain. This will create a tool that will have a truly transformative value in the hydrological and ecological sciences.</p>