Slow responses of understory plants of maple-dominated forests to white-tailed deer experimental exclusion

Amélie Collard,Line Lapointe,Jean-Pierre Ouellet,Michel Crête,Alain Lussier,Claude Daigle,Steeve D Côté

doi:10.1016/j.foreco.2010.05.021

Abstract

We examined the response of understory plants in mature maple-dominated forests of southern Québec, Canada, following about 30 years of high deer densities, using a deer exclosure experiment. An exclosure and a paired control of 625 m 2 each were established on six sites in 1998. An exclosure and a paired control of 16 m 2 were added at each of the same sites in 2003 but under a recent canopy gap to determine if light could enhance plant responses. We measured plant richness and abundance, and aboveground biomass of different plant groups for 8 years in the understory plots and for 3 years in the canopy gaps. Four herbaceous species were also monitored individually in the same plots. No significant differences between treatments were found in plots under forest cover, except for lateral obstruction at 0–50 cm height which was higher in the exclosures. Under canopy gaps, however, tree seedling and total plant abundance were higher in deer exclosures than in control plots. Trillium erectum recovered partially as individuals were taller, had larger leaves and more frequently produced a flower or a fruit in the absence of deer browsing under forest cover. To a lesser extent, Erythronium americanum and Maianthemum canadense also exhibited signs of recovery but were still at the single-leaf stage after 8 years of recovery. In general, the different plant groups exhibited little recovery following deer exclusion, possibly because of the low light levels that prevailed in the understory of undisturbed maple-dominated forests. The higher latitude of the present study could also contribute to the slow recovery rates of the different groups of plants compared to studies conducted in northeastern USA. Variability among sites and years had an effect on detection of statistically significant differences. Trends are however appearing over time, suggesting that many understory plants are recovering very slowly following deer exclusion. Our results emphasize the importance of studying large herbivore–forest interactions on different groups of plants, but also on specific species, and under different latitudes to be fully understood.

Highlights

Many populations of cervids occur at high population densities throughout much of their range
Deer habitat can change between winter and summer. They tend to agglomerate in yards in the winter often looking for a more abundant conifer cover, while they disperse in the summer throughout the forested areas
We investigated the impact of deer on understory vegetation in maple-dominated forests by evaluating the capacity of plants to recover following a relatively long period of intense herbivory

Summary

Introduction

Many populations of cervids occur at high population densities throughout much of their range. The negative impacts of deer browsing on the understory vegetation of temperate forests of northeastern North America are relatively well known (Rooney and Dress, 1997; Rooney, 2001; Russell et al, 2001; Rooney and Waller, 2003; Côté et al, 2004), our understanding of the capacity of plants to recover following long periods of intense herbivory is limited (Horsley et al, 2003; Webster et al, 2005).

Methods

Results

Discussion

Conclusion