Divergent responses to climate change and disturbance drive recruitment patterns underlying latitudinal shifts of tree species

Abstract

Climate change is expected to result in a reorganization of the continental distribution of tree species. Recent shifts in distribution patterns have been reported, but it is not always clear how climate change influences these patterns locally, especially in relation to other disturbances. We investigated latitudinal shifts of four ecologically important tree species between 1970 and 2014 within a study area that encompasses their northernmost range limit in northeastern North America (Quebec, Canada; ~761,000 km2). Changes in latitudinal limits were defined in relation to changes in tree saplings’ occurrence patterns within forest plots resampled over two time periods (1970–1977 and 2003–2014). By examining changes in the frequency of occurrences in different portions of the study area along a latitudinal gradient, we were able to identify spatially explicit patterns of loss or gain (sapling recruitment) resulting in the shifts observed. We then estimated the probability of observing a recruitment event in response to changes in climate, disturbance and their interaction, using a multimodel selection approach. Latitudinal limits of all four species shifted northward, but these shifts resulted from different patterns of plot occurrence changes, depending on the species and the location examined. Greater recruitment at northern locations than at southern ones drove shifts for Acer saccharum Marsh., Fagus grandifolia Ehrh. and Acer rubrum L., but less so for Betula alleghaniensis Britt. Climate variables indicating changes in early or late growing season conditions were most often selected in models. Warming tended to reduce recruitment probability in the south but increase it in the north, leading to divergent responses for a given species across the study area. Disturbance effects were generally less important than climate change effects, as was their interaction. Synthesis. Spatially explicit and divergent responses to climate change and disturbance drive recruitment patterns underlying latitudinal shifts of tree species. The importance of early‐ or late‐season climate variables points towards biological processes being affected at critical stages of the life cycle. Understanding the factors that influence species’ migration capacity in a changing climate is crucial to inform adaptive management and conservation practices.

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

“…Our results contrast with those of Boisvert‐Marsh et al (), who found that climate was more important than disturbances in explaining tree sapling recruitment at their northern limit in Québec. This suggests that the pattern we uncovered might be caused primarily by an increase in abundance of species already present rather than by new colonization.…”

“…As such, there is a growing body of evidence for contemporary shifts in tree species distributions along elevational gradients in mountains (Beckage et al, 2008;Lenoir, Gegout, Marquet, Ruffray, & Brisse, 2008;Savage & Vellend, 2015), where ecotones are narrow and well defined (Jump et al, 2009). Similar evidence is also beginning to emerge for latitudinal shifts (Boisvert-Marsh, Périé, & Blois, 2019;Fisichelli, Frelich, & Reich, 2014;Sittaro et al, 2017). However, because of the focus on shifts at range limits (e.g., leading and rear edges of species ranges), there has been little empirical work on the effect of climate change on tree community composition and abundance distributions within the core of the species range itself (e.g., Esquivel-Muelbert et al, 2018;Searle & Chen, 2017).…”

“…Leithead et al () also observed that the establishment of southern temperate species in the temperate–boreal ecotone of northern Ontario increased with the size and age of canopy gaps. Although Boisvert‐Marsh et al () found that climate change outweighs disturbances in explaining latitudinal shifts of tree saplings in Québec in the last decades, Danneyrolles et al () found larger impacts of anthropogenic disturbances than climate warming on forest compositional changes in southern Québec over the last centuries. Hence, to anticipate and adapt to future forest changes, large‐scale empirical studies are required in order to unravel individual and aggregated impacts of multiple stressors on forest composition.…”

“…Yet, disturbances and climate change have a high potential for interactions, which can lead to synergistic or antagonistic ecological effects that are difficult to predict (Brook, Sodhi, & Bradshaw, 2008). Indeed, disturbances create canopy openings that could facilitate the northward migration of temperate species (Boisvert-Marsh et al, 2019;Leithead, Anand, & Silva, 2010;Vanderwel & Purves, 2014;Xu, Gertner, & Scheller, 2012). In addition, the frequency and intensity of natural disturbances can increase as an indirect effect of climate change (Seidl et al, 2017).…”

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

“…This often involves a temporal mismatch between disturbances and the rate of climate change. First, if disturbances occur relatively infrequently, the effects of the shifting disturbance regimes may be minimal compared to shifting climatic variables (Boisvert‐Marsh, Périé, & de Blois, 2019). In other words, the velocity of climate change may be too fast and opportunities out of sync with life‐history constraints.…”