Disequilibrium of fire-prone forests sets the stage for a rapid decline in conifer dominance during the 21^st century

Abstract

As trees are long-lived organisms, the impacts of climate change on forest communities may not be apparent on the time scale of years to decades. While lagged responses to environmental change are common in forested systems, potential for abrupt transitions under climate change may occur in environments where alternative vegetation states are influenced by disturbances, such as fire. The Klamath mountains (northern California and southwest Oregon, USA) are currently dominated by carbon rich and hyper-diverse temperate conifer forests, but climate change could disrupt the mechanisms promoting forest stability– regeneration and fire tolerance— via shifts in the fire regime in conjunction with lower fitness of conifers under a hotter climate. Understanding how this landscape will respond to near-term climate change (before 2100) is critical for predicting potential climate change feedbacks and to developing sound forest conservation and management plans. Using a landscape simulation model, we estimate that 1/3 of the Klamath could transition from conifer forest to shrub/hardwood chaparral, triggered by an enhanced fire activity coupled with lower post-fire conifer establishment. Such shifts were more prevalent under higher climate change forcing (RCP 8.5) but were also simulated under the climate of 1950-2000, reflecting the joint influences of early warming trends and historical forest legacies. Our results demonstrate that there is a large potential for loss of conifer forest dominance—and associated carbon stocks and biodiversity- in the Klamath before the end of the century, and that some losses would likely occur even without the influence of climate change. Thus, in the Klamath and other forested landscapes subject to similar feedback dynamics, major ecosystem shifts should be expected when climate change disrupts key stabilizing feedbacks that maintain the dominance of long-lived, slowly regenerating trees.

Mixed‐severity wildfire and habitat of an old‐forest obligate

“…, Serra‐Diaz et al. ). The region has experienced short intervals between recent high‐severity fires coupled with intensive timber management in this mixed‐severity fire regime area, and the likelihood of further shortening of fire‐return intervals with climate change (Davis et al.…”

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

“…, Serra‐Diaz et al. ). However, Pacific Northwest forested landscapes are deficit of late seral forest (DeMeo et al.…”

“…, Millar and Stephenson , Serra‐Diaz et al. ). Such climate‐ and fire‐driven decreases in regeneration of obligate seeders and state transitions of forest to shrubfield have already been documented within other regions in western North America (Kemp et al.…”

“…, Serra‐Diaz et al. ). Ecosystem and species reorganization may be more likely in periods of rapid climatic change (Crausbay et al.…”

What's hot in conservation biogeography in a changing climate? Going beyond species range dynamics

“…The overall effect of disturbances, however, still requires further scrutiny. For instance, Liang, Duveneck, Gustafson, Serra‐Diaz, and Thompson () predicted little effect of disturbances on range edge shifts in NE United States forests while Serra‐Diaz et al () projected rapid conifer decline due to climate–fire interactions in western United State forests. Finally, niche and network approaches could be important for predicting ensembles of species under climate change (Godoy, Bartomeus, Rohr, & Saavedra, ), providing new avenues for research in conservation biogeography.…”