Chronic deer browsing leads to biotic homogenization of minerotrophic peatlands

Abstract

Peatlands could become important foraging habitats, and their plant communities threatened, in areas with an overabundance of large herbivores. Peatland response to herbivore exclusion may vary widely according to abiotic conditions and associated species because of a strong minerotrophic gradient. We assessed the impact of white-tailed deer (Odocoileus virginianus Zimm.) on peatland vegetation using an exclosure experiment. A total of 53 pairs of exclosures and unprotected plots were set up in bogs (13 pairs), sedge fens (20), shrub fens (7), and laggs (13), and surveyed prior to exclosure construction as well as three, five, and eight years after. Vascular plant composition of exclosures diverged from that of unprotected plots through time only in shrub fens and laggs. Bryophytes remained constant in all habitats. On average, shrub cover was 30% higher in exclosures in all habitats after five years, whereas herb cover increased only in laggs, by 43%, after eight years. Reclassification of sites by pH showed deer exclusion promoted alpha diversity in low- and high-moderate rich fens (pH 5.3–6.8) and beta diversity in the latter as well as in rich fens (pH 6.3–7.5). Overall, our results suggest that conservation efforts in areas with overabundant large herbivores should target richer peatland habitats since they showed a higher resilience and fostered alpha and beta diversity.

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver–response relationships to develop conceptual models across ecosystems

“…Top‐down trophic cascades have variable consequences for beta diversity among patches exposed to similar grazing pressure, although most studies have been completed at relatively small extents (10–100 km 2 ; Database S1). Across temperate regions in the Northern Hemisphere, increased grazing by deer and sheep was associated with biotic homogenisation of plants within grazed areas (Courchesne et al ., 2018; Holmes & Webster, 2011; Ohashi & Hoshino, 2014; Perea, Girardello & San Miguel, 2014; Rooney, 2009; Salgado‐Luarte et al ., 2019). However, in contrast to increased grazing pressure, experimental removal of grazers (i.e.…”

Large herbivores trigger spatiotemporal changes in forest plant diversity

“…Many studies, including a previous one at our study site on Anticosti Island, Québec (Hidding et al, 2013), have demonstrated effects of ungulate herbivory on community composition and successional trajectories (see also Conway & Johnstone, 2017; De Vriendt et al, 2021). There have also been studies of alpha diversity (see previous paragraph), but only a few studies have reported quantitative estimates of how ungulates influence beta diversity in forest plant communities (Mediterranean forests [Perea et al, 2014], boreal forest [Lilleeng et al, 2016], deciduous forests [Newman et al, 2014], boreal peatland [Courchesne et al, 2018]). None of these studies quantified temporal changes in beta diversity under controlled and replicated conditions (but see Speed et al, 2013 for an alpine ecosystem), and the relationships between alpha diversity, beta diversity, and community composition remain largely unexplored in deer–forest systems.…”