Compositional and functional trajectories of herbaceous communities after deer density control in clear-cut boreal forests

Abstract

Overabundant populations of large herbivores have strong persistent effects on forest composition, structure, and function. However, the mechanism through which plant communities recover their original composition and function after herbivore management remains poorly understood. We assessed the temporal trajectories of the herbaceous communities in Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss stands on Anticosti Island (Quebec, Canada) over 8 years following clear-cutting and deer management. The impact of deer exclusion or reduction to 7.5 and 15 deer·km–2 was compared with benchmark in situ deer densities (27 and 56 deer·km–2). Effects of deer management treatments on plant species and functional trait assemblages over time were assessed using principal response curves. Although complete deer exclusion seemed necessary to modify species composition from that occurring under intense browsing, a reduced density of 7.5 deer·km–2 was sufficient to induce significant changes in functional trait assemblages of regenerating stands. For instance, reduced deer densities favored plants with brightly colored flowers and compound inflorescences pollinated by animals and producing large seeds and fleshy fruits dispersed by animals. We conclude that the boreal forest’s herbaceous communities are resilient to chronic browsing when deer population reduction and forest clearcutting are applied in synergy.

Chronic deer browsing leads to biotic homogenization of minerotrophic peatlands

“…Among the species characterizing unprotected plots of shrub fens and laggs, Dasiphora fruticosa is a shrub resistant to herbivores (Lovaas 1958;Elkington and Woodell 1963) but known to be highly browsed on Anticosti Island (Pellerin et al 2006), likely due to the scarcity of other resources, as suggested by Elkington and Woodell (1963). Five graminoid species remained associated with browsing in both shrub fens and laggs, reinforcing comments above concerning the high ability of these plants to persist in browsed environments (Stockton et al 2005;Rooney 2009;Bachand et al 2015).…”

From delayed succession to alternative successional trajectory: How different moose browsing pressures contribute to forest dynamics following clear‐cutting

“…A deer exclusion experiment on Anticosti Island also found a decrease in Cornus canadensis biomass with increasing deer density (Tremblay et al, 2006). In this system, deer browsing was a causal factor for a shift from forested ecosystems toward savannas dominated by spruce and grasses (Hidding et al, 2013;Bachand et al, 2015). Gosse et al, 2011].…”

“…The initial floristic composition shapes the composition and structure of the following ecological communities (Egler, 1954). By repeatedly and selectively foraging on plants before and after a disturbance, large herbivores may shape the early-successional species composition, leading to alternative successional trajectories (Hidding et al, 2013;Bachand et al, 2015;Kolstad et al, 2018) and thus, potentially conducing to changes in forest composition, structure and processes that are difficult to reverse (Scheffer and Carpenter, 2003;Barrette et al, 2014;Franklin and Harper, 2016). For example, high ungulate density has been linked to reduced N mineralization and net primary production in forests (Pastor et al, 1993), and to shifts from closed to open forests (McLaren et al, 2004;Gosse et al, 2011).…”

Large herbivores trigger spatiotemporal changes in forest plant diversity

“…Increases in abundance have been observed for more browsing-tolerant species such as graminoids (e.g., Calamagrostis canadensis, Poaceae spp., Carex spp. ), thistles (Cirsium arvense and C. vulgare), ferns (e.g., Pteridium aquilinum, Gymnocarpium dryopteris), Equisetum spp., and spruces (P. glauca and P. mariana) (Bachand et al, 2015;Potvin et al, 2003;Tremblay et al, 2006).…”