Understanding the Drivers of Variability in Forest Structure and Composition in North American Boreal Forest

Abstract:

Boreal forests are expected to advance northward as the result of persistent warming in the northern latitudes, resulting in changes to the structure and function of the high-northern latitudes. However, the rates and patterns of forest expansion are heterogeneous and the environmental drivers that lead to the shift from tundra to forest are poorly understood. Predictions of changes in vegetation across the Taiga Tundra Ecotone (TTE) must incorporate multiple scales and often opposing feedback mechanisms. The variability of patterns and processes that determine woody structure is linked to numerous controlling factors, including: climate, site history and local conditions associated with hydrology, permafrost, soil, bedrock depth, snow cover and wind. Ecological modeling has been effective at integrating the effects of the multi-scale controls across boreal forests in this region. The goal of our Arctic-Boreal Vulnerability Experiment (ABoVE) Phase 2 research is to examine and quantify the likelihood of predicted changes in TTE forest structure patterns occurring within the ABoVE extended domain, using airborne imagery and lidar observations, site-scale (i.e., high resolution spatially-explicit individual-based) forest and tundra vegetation modeling, and a Landsat-derived map of the extent & pattern of the TTE. Here, we present high resolution forest modeling simulation results, tested at ten TTE sites across the ABoVE domain. We analyzed forest structure and composition metrics across these focal sites to understand current forest patterns along topographic, soil and climatic gradients at 10m-pixel resolution. Our results provide a deeper understanding of the current productivity dynamics along the TTE, and will allow for informed prognostication about the shift in the extent of tree cover, and the spatial variability in the direction, rate, and magnitude of these shifts.