Slow responses of ecosystems to reductions in deer (Cervidae) populations and strategies for achieving recovery

Abstract

Large mammalian herbivores significantly alter the functioning of a range of ecosystems worldwide. One family of herbivores in particular, deer (Cervidae), have become widespread throughout temperate regions over the last century. Culling is frequently used to reduce the ecological impacts of deer, but recent studies demonstrate that the recovery of herbivore-disturbed vegetation is often a protracted process on the order of decades. Here, we ask why increases in deer-preferred plants occur slowly following culling and what generalities can inform management of the responses of vegetation to deer culling? Vegetation changes following deer population reduction may be slow because of the: (i) slow growth rate of plants relative to the amount of biomass consumed by herbivores; (ii) depletion of seed sources of deer-preferred plants; (iii) formation of alternate vegetation types under high deer browsing; (iv) preferential browsing of forage even under low deer densities; (v) variation in browse damage of deer-preferred species with plant community composition (e.g. associational resistance or susceptibility); (vi) suppression of trophic cascades; and (vii) changes in abiotic conditions associated with other ecological processes. Managers can accelerate recovery through different active management strategies that directly address the reasons behind slow recovery. However, while the ecology behind the impacts of deer, and to a certain extent their mitigation, are largely understood, a significant obstacle to achieving recovery often lies in implementing science-based management recommendations, e.g. culling, and their societal acceptance. Bridging the science-policy-practice gap requires that applied ecologists share common language and values with policymakers and the public. Recovery may hinge as much on bridging this communication gap as on improving our ecological understanding of deer impacts and ecosystem recovery.