Accounting for landscape heterogeneity improves spatial predictions of tree vulnerability to drought

Abstract

As climate change continues, forest vulnerability to droughts and heatwaves is increasing, but vulnerability varies regionally and locally through landscape position. Also, most models used in forecasting forest responses to heat and drought do not incorporate relevant spatial processes. In order to improve spatial predictions of tree vulnerability, we employed a nonlinear stochastic model of soil moisture dynamics accounting for landscape differences in aspect, topography and soils. Across a watershed in central Texas we modeled dynamic water stress for a dominant tree species, Juniperus ashei, and projected future dynamic water stress through the 21 century. Modeled dynamic water stress tracked spatial patterns of remotely sensed drought-induced canopy loss. Accuracy in predicting drought-impacted stands increased from 60%, accounting for spatially variable soil conditions, to 72% when also including lateral redistribution of water and radiation/temperature effects attributable to aspect. Our analysis also suggests that dynamic water stress will increase through the 21 century, with trees persisting at only selected microsites. Favorable microsites/refugia may exist across a landscape where trees can persist; however, if future droughts are too severe, the buffering capacity of an heterogeneous landscape could be overwhelmed. Incorporating spatial data will improve projections of future tree water stress and identification of potential resilient refugia.

Hillslope Hydrology in Global Change Research and Earth System Modeling

“…Without this inherent coupling and assuming uniform soil water status across an ESM grid cell, it would be difficult to predict the continued transpiration from the aspen forest through the entire growing season. This ridge‐to‐valley subsidy also occurs in seasonally dry climates where abundant wet season precipitation recharges the regolith and groundwater (Goulden et al, ; Schwantes et al, ; Swetnam et al, ; Tai et al, ). Groundwater flow converges toward the valleys with a delay, and continues into the dry season, because groundwater moves slowly.…”

Plant Hydraulic Stress Explained Tree Mortality and Tree Size Explained Beetle Attack in a Mixed Conifer Forest

“…Topographic gradients create variations of local water supply and energy demand (Fan, ; Tai et al, ). Coupling plant hydraulics with hydrological models allows mechanistic characterizations of plant hydraulic stress across the landscape (Mencuccini et al, ) and has been useful to predict the spatial pattern of tree morality mediated by variations in physical environment (e.g., water availability) induced by topography (W. R. Anderegg et al, ; Schwantes et al, ; Simeone et al, ; Tai et al, ).…”

Validating climate‐change refugia: empirical bottom‐up approaches to support management actions

“…; Schwantes et al . ). However, these methods merely establish a spatial hypothesis of where climate buffering may occur, which is not an end in itself but rather a starting point toward ensuring that natural lands managers can identify, protect, and manage climate‐change refugia.…”