Analog‐based fire regime and vegetation shifts in mountainous regions of the western US

Abstract

Climate change is expected to result in substantial ecological impacts across the globe. These impacts are uncertain but there is strong consensus that they will almost certainly affect fire regimes and vegetation. In this study, we evaluated how climate change may influence fire frequency, fire severity, and broad classes of vegetation in mountainous ecoregions of the contiguous western US for early, middle, and late 21st century (2025, 2055, and 2085, respectively). To do so, we employed the concept of a climate analog, whereby specific locations with the best climatic match between one time period and a different time period are identified. For each location (i.e. 1‐km2 pixel), we evaluated potential changes by comparing the reference period fire regime and vegetation to that of the fire regime and vegetation of the nearest pixels representative of its future climate. For the mountainous regions we investigated, we found no universal increase or decrease in fire frequency or severity. Instead, potential changes depend on the bioclimatic domain. Specifically, wet and cold regions (i.e. mesic and cold forest) generally exhibited increased fire frequency but decreased fire severity, whereas drier, moisture‐limited regions (i.e. shrubland/grassland) displayed the opposite trend. Results also indicate the potential for substantial changes in the amount and distribution of some vegetation types, highlighting important interactions and feedbacks among climate, fire, and vegetation. Our findings also shed light on a potential threshold or tipping point at intermediate moisture conditions that suggest shifts in vegetation from forest to shrubland/grassland are possible as the climate becomes warmer and drier. However, our study assumes that fire and vegetation are in a state of equilibrium with climate, and, consequently, natural and human‐induced disequilibrium dynamics should be considered when interpreting our findings.

Living on the edge: trailing edge forests at risk of fire‐facilitated conversion to non‐forest

“…, Parks et al. ). The first variable, climatic moisture deficit (CMD; mm/yr), was obtained from the ClimateNA dataset (resolution = 1 km; AdaptWest Project , Wang et al.…”

“…Following Parks et al. (), we utilized climate analogs (Hamann et al. , Dobrowski and Parks ) to infer the distribution of forest cover for the reference period and mid‐21st century (Figs.…”

“…For example, species distribution models (SDMs) and bioclimatic envelope models are often used to evaluate range shifts of individual species (Guisan et al 2007, McKenney et al 2007, Iverson et al 2008. Recently, climate analog models have been used in conjunction with gridded climate data to evaluate potential shifts in vegetation distribution (Batllori et al 2017, Parks et al 2018a) and potential effects on ecosystem services such as crop yields (Pugh et al 2016). Although these and conceptually similar models are useful, they assume that the current and future distribution of any given species or vegetation type is in equilibrium with climate (Heikkinen et al 2006, Ara ujo andPeterson 2012; i.e., that changes in climate result in immediate change in vegetation).…”

The missing fire: quantifying human exclusion of wildfire in Pacific Northwest forests, USA

“…We also do not explicitly evaluate the potential impacts of current and projected future climate change on fire regimes but note that long‐term changes in fire regimes may move in different and counterintuitive directions than more immediate changes (McKenzie and Littell , Parks et al. ). Nor have we addressed how historic fire regimes may have adapted to climate change in the absence of fire suppression and other twentieth‐century land management (e.g., future range of variation; Gartner et al.…”

Climate change likely to reshape vegetation in North America's largest protected areas

“…Vegetation changes were evaluated using the climate analog model, where, for any given pixel in a PA, we identified the vegetation in the nearest locales with current climate conditions that match its projected future climate (c.f., Batllori et al, 2017;Parks et al, 2018). We used gridded vegetation maps for each country to define reference conditions for each PA, and estimated the potential for change for two future time periods representing mid-and late-21st century.…”