Priority effects will impede range shifts of temperate tree species into the boreal forest

Abstract

1. Temperate tree species are expected to expand their distribution into the boreal forest in response to climate change. However, it is becoming increasingly clear that many species will experience significant setbacks in capacity to migrate due to a series of unfavourable conditions impacting their recruitment success, and thus their ability to colonize new locations.2. We quantify the relative influence of a series of factors important for tree seedling recruitment at range margins: propagule dispersal, substrate favourability and the influence of the local hetero-specific species canopy composition. We hypothesized that boreal trees are responsible for priority effects that influence the establishment of temperate tree species seedlings. To do so, we analysed two recruitment stages (firstyear seedlings and older seedlings) for seven tree species: Abies balsamea (ABBA), Acer rubrum (ACRU), Acer saccharum (ACSA), Betula papyrifera (BEPA), Betula alleghaniensis (BEAL), Populus tremuloides (POTR) and Fagus grandifolia (FAGR) commonly found within the temperate-boreal ecotone forests of northeastern North America.3. Overall, we found that boreal canopy trees influence the distribution of substrates, more specifically the occurrence of needle cover and decayed wood in recruitment plots. Interestingly, decayed wood was a poor substrate in almost all cases. This association between canopy and substrate led to highly unfavourable substrates that affected the seedling densities of all temperate tree species. In addition, we found that seedling dispersion was highly localized, where the mean dispersal distance of all trees occurred in close proximity of parent trees. 4. Synthesis. Unfavourable substrates and limited mean dispersal distance of trees due to resident boreal trees generate (strong) priority effects within the temperate-boreal ecotone. Together, these conditions promise to cause significant lags in temperate tree species migration into the boreal forest in the future. K E Y W O R D Sboreal forest, climate change, ecotone, priority effects, recruitment, species migration, species range, temperate forest

Slow demography and limited dispersal constrain the expansion of north‐eastern temperate forests under climate change

“…However, given that our model detects disequilibrium in the present distribution of temperate forest, it is clear that change in forest composition is already occurring in our data. Further, we still found significant lags after extending the cell size way beyond the dispersal kernel of most temperate trees (Clark et al, 1998;Ribbens et al, 1994;Solarik et al, 2019). Thus, attaining similar rates of change to those observed in palaeoecological studies would require a rapid increase in transition from temperate to mixed and mixed to boreal forest, which would be possible if climatic tipping points result in little change in the early phases of warming followed by a period of rapid changes (Schaphoff et al, 2016).…”

“…For example, strong competition at range margins can reduce the intrinsic growth rate, which, coupled with dispersal limitations, might contribute to slow colonization (Godsoe et al, 2017). Plant-soil feedbacks, seed dispersers, mycorrhizae and other types of biotic interactions also contribute to local forest dynamics and consequently have potential implications on large-scale range dynamics (Solarik et al, 2019).…”

Climate‐induced variation in the demography of 14 tree species is not sufficient to explain their distribution in eastern North America

“…Although competition for light is important, our results show that there might be other mechanisms underlying abundance or population growth rates. For example, certain species have undergone negative density dependence (Yenni et al., 2012, for rare species), whereas certain common species are limited by plant–soil feedbacks (Solarik et al., 2020, Acer saccharum ).…”

Soil chemical legacies trigger species-specific and context-dependent root responses in later arriving plants

“…Depending on the biological mechanism(s) responsible for niche modification, late-arriving species can either be inhibited or facilitated by early-arriving species (Fukami, 2015;Delory et al, 2019a). Although niche preemption plays an important role in the creation of priority effects in plant communities (Kardol et al, 2013), the relative importance of niche modification mechanisms in creating priority effects certainly deserves more attention (Solarik et al, 2020;Halliday et al, 2020).…”