Research Branch

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The Ecological Roles of Wildlife Tree Users in Forest Ecosystems

Author(s) or contact(s): M.M. Machmer and C. Steeger
Source: Research Branch
Subject: Ecosystems
Series: Land Management Handbook
Other details:  Published 1995. Hardcopy is available.


This report synthesizes North American literature about the effects of wildlife tree users on invertebrate and vertebrate pest populations. The feeding habits of 92 species of wildlife tree users in British Columbia are described along with the forest pest species (vertebrate and invertebrate) they prey on. By examining the trophic relationships of wildlife tree users, knowledge of their other ecological roles is gained. These roles are identified and discussed in the context of forest management. Management recommendations and research directions are discussed.

Wildlife tree users are arranged into foraging guilds, and studies that investigate the effects of individual species or entire guilds on the abundance and distribution of forest pests are reviewed. These effects are quantified when possible and anecdotal information is presented and discussed for guilds where quantitative studies are lacking. This information is used to evaluate the potential capacity of specific wildlife tree users to regulate forest pests in a density-dependent manner.

The impact of wildlife tree users on forest pests is most apparent in the bark-foraging and foliage-gleaning guilds, which have been studied extensively. Members of these groups (e.g., woodpeckers, nuthatches and chickadees)exert a direct influence on pest abundance, exhibiting functional and numerical responses to increases in pest density. They also affect pest abundance indirectly by altering the microclimate of their prey and by increasing pest susceptibility to other mortality agents such as parasitism, predation, disease and weather. The relative effect of predation by these guilds is greatest at low pest densities; thus they play a significant role in maintaining pests at endemic levels by delaying the onset of outbreaks or by accelerating their decline. The ground-and aerial-foraging (hawking) birds, terrestrial and arboreal rodents, and aerial-foraging and gleaning bats all consume injurious insects. However, the quantitative effect of these wildlife tree-using guilds on pest populations requires further investigation. There is little evidence that vertebrate forest pests are regulated by wildlife tree-dependent carnivorous birds and mammals. However, their actions may reduce pest damage by slowing the rate of an outbreak, accelerating its decline, or interacting with density-dependent factors to lower equilibrium pest densities.

Other ecological roles of wildlife tree users in British Columbia include dispersing mycorrhizal inoculum, seeds and other materials, providing nesting, feeding and roosting opportunities for wildlife, accelerating decomposition in dead and decaying trees, nutrient cycling, transmitting tree and insect pathogens, consuming seeds, and damaging healthy trees.

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Updated May 03, 2007