Competition mediates understorey species range shifts under climate change

Abstract

1. Biological communities are reshuffling owing to species range shifts in response to climate change. This process inherently leads to novel assemblages of interacting species. Yet, how climatic change and local dynamics in biotic interactions jointly affect range shifts is still poorly understood.2. We combine a unique long-term transplant competition-exclusion experiment with species distribution models (SDMs) to test the effects of biotic interactions on understorey species range shifts under climate change in European temperate forests. Using a time series of 18 years of individual-level demographic data of four common understorey plant species transplanted beyond their cold range edge to plots with and without interspecific competition, we built integral projection models (IPMs) and analysed the effects of competition on five key vital rates and population growth (λ). We assessed the results of the transplant experiment in the context of the modelled species' current and future potential distributions.3. We find that species' population performances in the transplant experiment decreased with lower predicted habitat suitability from the SDMs. The population performance at the transplant sites was mediated by biotic interactions with the local plant community: for two species with intermediate levels of predicted habitat suitability at the transplant sites, competition effects could explicitly differentiate between net population growth (λ > 1) or shrinkage (λ < 1). Synthesis.Our findings contest the long-standing idea that at cold range edges, mainly abiotic factors structure species' distributions. We conclude that biotic interactions, through acting on local population dynamics, may impact species distributions at the continental scale. Hence, predicting climate-change impacts on biodiversity redistributions ultimately requires us to also integrate dynamics in biotic interactions.

Ecological indicator values of understorey plants perform poorly to infer forest microclimate temperature

“…Degree‐scale, or “biogeographic” EIVs are not exempt from errors and may also be biased; for instance, a given species may be excluded by dispersal limitation, edaphic conditions or biotic factors from a climatically suitable area, which will then wrongly be considered as unsuitable. Therefore, fundamental climatic niches are usually wider than realized ones (Soberón & Arroyo‐Peña, 2017; Sanczuk et al., 2022), which are the ones used to derive EIVs. However, our results on vascular plants demonstrate a clear, if not direct link between a degree‐scale EIV and microclimate measurements of temperature annual range in lowland forests, which might open up new opportunities for quantifying the buffering effect in lowland forests using plant communities.…”

“…Therefore, fundamental climatic niches are usually wider than realized ones (Soberón & Arroyo-Peña, 2017;Sanczuk et al, 2022), which are the ones used to derive EIVs. However, our results on vascular plants demonstrate a clear, if not direct link between a degreescale EIV and microclimate measurements of temperature annual range in lowland forests, which might open up new opportunities for quantifying the buffering effect in lowland forests using plant communities.…”

High landscape‐scale forest cover favours cold‐adapted plant communities in agriculture–forest mosaics

“…We chose to emphasize the presence of cold-adapted species in 'forested' plots as they are the most threatened by climate change, and are most discussed in recent conservation literature (Hylander et al, 2022). In addition, our regional cooling interpretation complements the current literature on the potential protection forest microclimate offers in the warm edge of the distribution of cold-adapted species Sanczuk et al, 2022).…”

“…One could therefore expect that landscape‐scale forest cover could benefit plant species by cooling the hotter and drier (mean and extreme) conditions in spring and summer that could induce the dieback of vulnerable species. In these landscapes, the community could also be comprised of cold‐adapted species because they can outcompete the warm‐adapted species located at the cold edge of their distributions (Sanczuk et al, 2022). Highly forested landscapes could also influence plant community composition and favour cold‐adapted species through other means.…”

Density‐dependent species interactions modulate alpine treeline shifts

“…The former can be measured by simple indicators such as individual growth rate, changes in biomass and reproduction (Bishop et al, 2012;Chu et al, 2008;Lyu & Alexander, 2022;Wright et al, 2014). The latter is commonly investigated at the population level, requiring long-term and large-scale observations (Freeman et al, 2018;Shriver et al, 2021;Zhang et al, 2015), laboratory experiments (Legault et al, 2020) and modelling approaches (Filazzola et al, 2018;Sanczuk et al, 2022;Wieczorek et al, 2017). Inferences drawn from these two types of responses are often inconsistent.…”