Species dependent on OG

The following text is adapted from Old-growth forests of the Acadian Forest Region by A. Mosseler, J.A. Lynds, and J.E. Major. Environmental Reviews 11: S47–S77 (2003). See the original article for reference citations.

Species at risk associated with old growth
Old growth is a stage of forest development that represents a unique physical environment in terms of light, moisture, nutrients, organic matter, and the temporal stability of biomass structures to which some species (e.g., lichens) have become adapted. Relatively few animal species are known to be absolutely dependent on, or restricted to, the relatively undisturbed OG forests of eastern North America. However, several native vertebrates prefer such an environment, or at least certain components of it, to facilitate particular aspects of their life history:

– Cavity-nesters, such as owls, bats, and woodpeckers, require larger, partially decayed, older trees as nesting sites.
– Some birds forage under the deeply furrowed or plated bark of old spruce and hemlock trees (e.g., brown creepers, Certhia spp.) or prefer older, closed forest cover (e.g., Swainson’s thrush, Catharus ustulatus).
– Other mammals, reptiles, and amphibians in the forests of the Northeast require fallen coarse woody debris to avoid predation.
– Certain species of lichens require the long temporal stability of older trees to establish themselves on bark and branches.
– There are also herbaceous species and arthropods adapted to relatively undisturbed, older forests.

In the Pacific Northwest, bats (Myotis spp.) and cavity-nesting birds were the vertebrate species most likely to be either closely associated with, or dependent on, OG forests, but it was the canopy structures, snag densities, and levels of fallen trees, more than stand age per se, that determined habitat suitability for most species of forest-dependent plants and animals.

Vertebrate species associated with certain structural features of older forests have been identified for the various forest cover types of New Brunswick. They include such species as

for old, shade-tolerant hardwood forest types:
– downy woodpecker (Picoides pubescens)
– pileated woodpecker (Dryocopus pileatus)
– eastern woodpewee (Contopus virens)
– white-breasted nuthatch (Sitta carolinensis)
– black-throated blue warbler (Dendroica caerulescens)

for old spruce–fir forest types
– American marten (Martes americana)
– black-backed woodpecker (Picoides arcticus)
– red-breasted nuthatch (Sitta canadensis),
– red crossbill (Loxia curvirostra)
– white-winged crossbill (Loxia leucoptera)
– evening grosbeak (Coccothraustes vespertinus)
– olive-sided flycatcher (Contopus borealis)
– winter wren (Troglodytes troglodytes)
– golden-crowned kinglet (Regulus setrapa)
– ruby-crowned kinglet (R. calendula)
– solitary vireo (Vireo solitarius)
– Cape May warbler (Dendroica tigrina)
– blackburnian warbler (D. fusca)
– bay-breasted warbler (D. castanea)
– pine siskin (Carduelis pinus)

older mixedwood forests
– northern flying squirrel (Glaucomys sabrinus)
– Swainson’s thrush (Catharus ustulatus)
– along with other species

Average patch sizes of 20–30 ha are required for most birds and smaller mammals, with the exception of “umbrella species”, such as the American marten, that require larger patches of at least 375 ha (Anonymous 2001).

In Fennoscandian boreal forests, it has been estimated that more than 400 species of wood-dwelling beetles and over 200 species of cryptogams are at risk because large-diameter dead trees and logs are a sparse resource under modern logging regimes. Comparable studies are not available for the AFR.

There are likely to be many important species dependencies on OG that have yet to be identified. Therefore, the precautionary principle and our general knowledge of ecological and evolutionary relationships allow us to assume that, when a unique environment is available, various life forms will become adapted to it, especially if this environment once dominated a large portion of the pre European settlement landscape. The focus on unique environments, such as OG, recognizes that biodiversity management decisions should be focused at the community and landscape levels, rather than on the monumental task of focusing on individual species.