icbabs1

SOME PASSAGES ON WILDLIFE AND SNAGS, CAVITY USE, AND DOWN WOOD

Extracted from: Terrestrial Ecology Assessment Chapter, Science Integration
Team ecological assessment, Interior Columbia Basin Ecosystem Management
Project (ICBEMP) (draft chapter dated 18 April 1996)

Authors: Bruce G. Marcot, Mike Castellano, John Christy, Lisa Croft, John
Lehmkuhl, Robert Naney, Roger Rosentreter, Roger Sandquist, Elaine Zieroth

Following are sample passages on snags, cavity use, and down wood use by
species, taken from the text of the draft terrestrial ecology chapter. This
document is meant merely to indicate some of the key findings of the study.

For the full story, please review the full text of the chapter (when
available). Also, much additional information on these topics is available in
the tables, figures, and appendices in the chapter; in the Species-Environment
Relations (SER) data base of the interior Columbia River Basin assessment
area; in additional information "on file" (in the administrative files) of the
ICBEMP office, Walla Walla WA; and forthcoming in several USDA Forest Service
General Technical Reports.

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ON SNAGS

Lichens:

Natural forest burns generally leave clumps of unburned trees with intact
lichens and even portions of lichens on burned trees and snags.

Invertebrates:

Down wood, snags, specific habitat features (such as hydrological functions of
bogs and springs), forbs, shrubs, and trees of various species and sizes are
features to which predaceous arthropods are correlated, much like vertebrates.

Trees killed by insects are used as wildlife habitat both as standing snags
and down wood.

One opportunity that is beginning to be examined is the manipulation of bark
beetles using semiochemicals to produce snags for wildlife.

The carib beetle Pterostichus protractus (Carabidae) associates with fallen
woody debris and litter, as well as with bases of herbaceous plants, rocks,
and snags.

Vertebrates:

It is recognized that some species of bats use snags and other large trees,
either the cavities or deep-furrowed bark, for roosting.

However, it is not well understood how forest structures and landscape
patterns around the snag or tree influences site selection by bats.

Other conditions providing for bats include mature forests with high snag
densities and healthy riparian and wetland areas that provide foraging
habitat.

Anecdotal information on declines in numbers of bats in local areas is related
to reduction in the number of large snags.

Species showing habitat losses over the historical period were closely
associated with ponderosa pine cover types (especially single-story old-forest
stands); other single- or multi-story old-forest structural stages of forest
development; native grasslands and shrublands, especially native bunchgrass,
sagebrush and other shrub-steppe habitats; riparian cottonwood-willow, and
herbaceous and shrub wetland habitats; and large snag, defective-tree, or log
microhabitats.

General species association:

Another forest component is the presence of dead standing trees or snags.
Primary cavity excavator birds include some 17 species (3 chickadees, 3
nuthatches, and the rest woodpeckers). Beyond these 17 species are an
additional 29 species of vertebrates that closely associate with snag
substrates. These include 3 amphibians, 3 raptors, 7 bats, and 3 carnivores,
which use a variety of specific snag characteristics for a wide variety of
purposes.

Interestingly, our investigations uncovered a small set of species that seem,
in part, to specialize on bark piles at the base of snags.

Partially decomposed standing wood provides nest, feeding, and roost sites for
many other species (see summaries above under species associated with snags,
dead parts of live trees, and exfoliating bark); decomposing down wood is also
used by a variety of other species (see summary above under species associated
with down wood and litter and duff).

Management practices:

Threats to species that require late forests succession and associated
structural components such as large snags and down, woody debris include the
reduction or loss of these components, changes in wood decay rates, and
declines in insect (primarily ant) populations (Bull and others 1995).

Competition for cavities may be high in forest conditions lacking trees or
snags of adequate dbh with cavities.

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ON CAVITY USERS

Invertebrates:

One invertebrate in particular, the carpenter ant Camponotus modoc aids in
decomposition of standing and down wood. It operates at the hub of a complex
ecological process involving insectivore predatory birds, primary and
secondary cavity nesters, and defoliators.

Vertebrates:

Among the vertebrate “decreaser” species using old forests were the primary
cavity-excavating woodpeckers, which provide cavities and inner-tree access
for a wide variety of other fungi, plant, and animal species.

Among vertebrates, at least one amphibian (Coeur d'Alene salamander), no
reptile, 12 birds (including 5 raptors, 4 primary cavity excavators, and
others), and 3 mammals (American marten, heather vole, and woodland caribou)
show particular correlations to canopy condition.

Primary cavity excavator birds include some 17 species (3 chickadees, 3
nuthatches, and the rest woodpeckers).

The 17 vertebrate species that function as primary cavity excavators in trees
include 11 woodpeckers, 3 nuthatches, and 3 chickadees (chestnut-backed
chickadee, included here, is an occasional primary cavity excavator).

At least another 14 species act as secondary cavity users, using natural tree
cavities or cavities created by the primary excavators, for roosting or
nesting.

Northern saw-whet owls nest early in the season and thus may displace other
later-nesting secondary cavity users.

Likewise, boreal owls occupy larger tree cavities and nest earlier than many
other secondary cavity users, and may displace flying squirrels.

Management practices:

In recent decades, management practices have also reduced some habitat
attributes within various cover types and structural stages, primarily large,
standing dead trees and large down woody material. The distribution and
abundance of many species, including the cavity excavators and secondary
cavity users, have been adversely affected.

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ON DOWN WOOD

Bryophytes:

A similar situation exists in the Columbia River basin, especially in the
"maritime extension" areas of Idaho and Montana, where [bryophyte] species
depend on shade, wet soils, logs and other organic debris, and humid
microclimate.

Invertebrates:

Disruption of the duff/litter layer has immediate effects on water and thermal
relations, degrades habitat for many functional [invertebrate] species groups
that inhabit woody debris and litter, and alters forb and flowering plant
communities.

In some cases, maintaining predatory function may be as simple as maintaining
structures within the landscape that predators are known to require, such as
Camponotus modoc use of down wood.

An example illustrating the intricacy of predation effects is the central
importance of down wood. Because Camponotus modoc nests only in large
diameter down wood, maintenance of adequate large-diameter wood will favor
larger populations of this important spruce budworm predator.

Further, since Camponotus modoc is also the primary prey of pileated
woodpeckers, and since these woodpeckers excavate cavities used by a variety
of insectivorous birds, management of down wood can provide substantial
benefit by encouraging the maintenance of larger populations of budworm
predators, principally ants and birds.

Trees killed by insects are used as wildlife habitat both as standing snags
and down wood.

One invertebrate in particular, the carpenter ant Camponotus modoc aids in
decomposition of standing and down wood.

Vertebrates:

A few [amphibian] species, such as the Larch Mountain salamander, may lay eggs
in moist habitats but are associated with down wood or talus as adults, rather
than aquatic environments.

Distribution and abundance of many amphibian species seen more closely
associated with specific substrates (such as down wood) and microhabitat
conditions (such as deep, moist talus), than with general vegetation cover
types and structural stages.

Collectively, these amphibians are most sensitive to changes in down wood,
litter, and duff depths and characteristics; still and flowing water quality
and quantity; and precipitation quality and weather patterns.

Management practices:

In recent decades, management practices have also reduced some habitat
attributes within various cover types and structural stages, primarily large,
standing dead trees and large down woody material.

Species associated with down wood:

Among the listed, candidate, or potential candidate species of plants, 46
fungi species, the decayed wood bryophyte group, and 5 lichen groups were
identified in the database as associated with down wood. At least 11
invertebrate species were identified as examples of the several thousand
species associated with down wood. Two examples are the checkered beetle,
Enoclerus sphegeus (Cleridae), which uses both fresh down wood and also intact
but older down wood; and the leafcutting bee Osmia bruneri (Megachilidae),
which uses snags and stumps, but also uses down wood stems with abandoned
beetle burrows. Additionally, 82 species of amphibians, reptiles, birds, and
mammals show correlations with down wood.