Disturbances amplify tree community responses to climate change in the temperate–boreal ecotone

Abstract

Aim Climate change causes major shifts in species distributions, reshuffling community composition and favouring warm‐adapted species (“thermophilization”). The tree community response is likely to be affected by major disturbances, such as fire and harvest. Here, we quantify the relative contributions of climate change and disturbances to temporal shifts in tree composition over the last decades and evaluate whether disturbances accelerate community thermophilization. Location Québec, Canada. Time period 1970–2016. Taxa studied Trees. Methods Using 6,281 forest inventory plots, we quantified temporal changes in species composition between a historical (1970–1980) and a contemporary period (2000–2016) by measuring temporal β‐diversity, gains and losses. The effects of climate and disturbances on temporal β‐diversity were quantified using multiple regressions and variation partitioning. We compared how community indices of species temperature preference (CTI) and shade tolerance (CSI) changed for forests that experienced different levels of disturbance. We quantified the contribution of species gains and losses to change in CTI. Results Temporal β‐diversity was mainly driven by disturbances, with historical harvesting as the most important predictor. Despite the prevailing influence of disturbances, we revealed a significant thermophilization (ΔCTI = +.03 °C/decade) throughout forests in Québec. However, this shift in community composition was weakly explained by climate change and considerably slower than the rate of warming (+.14 °C/decade). Importantly, thermophilization was amplified by moderate disturbances (+.044 °C/decade), almost a threefold increase compared with minor disturbances (+.015 °C/decade). The gains and losses of a few tree species contributed to this community‐level shift. Conclusions Our study provides evidence that disturbances can strongly modify tree community responses to climate change. Moderate disturbances, such as harvesting, might reduce competition and facilitate gains of warm‐adapted species, which then accelerate thermophilization of tree communities under climate change. Although accelerated by disturbances, community thermophilization was driven by the gains and losses of a small number of species, notably gains of maples.

Leading‐edge disequilibrium in alder and spruce populations across the forest–tundra ecotone

“…5). These observations are consistent with previous work showing that disturbances can produce changes in vegetation growth and composition that outpace the near‐term effects of climate change (Landhäusser and Wein 1993, Lantz et al 2010, 2013, Brice et al 2019). This suggests that increases in the rate and frequency of Arctic and sub‐Arctic fires (Flannigan et al 2006) will have a significant impact on the magnitude and timing in vegetation change for both spruce and alder.…”

Degrees of compositional shift in tree communities vary along a gradient of temperature change rates over one decade: Application of an individual-based temporal beta-diversity concept

“…Legendre and his collaborators applied the loss/gain partitioning procedure for temporal beta-diversity to many empirical datasets (e.g., Kuczynski et al . 2018, Brice et al . 2019), and constructed a new analytical trend in temporal beta-diversity.…”

Disturbances as opportunities: Learning from disturbance‐response parallels in social and ecological systems to better adapt to climate change

“…Disturbances can facilitate ecological adaptation (Thom, Rammer, & Seidl, 2017), for example by enhancing species' migratory opportunities (Brice, Cazelles, Legendre, & Fortin, 2019; Landhäusser, Deshaies, & Lieffers, 2010; Mori, Isbell, & Seidl, 2018; Wang et al, 2019) assuming species are present to take advantage. This may mean transformation, such as from forest to shrublands, as well as species substitution within the current dominant ecosystem (e.g.…”