Wildlife Considerations in Modern Forest
Management
By John P. Hayes
Professor
of Wildlife Ecology, Oregon State
University
In recent
years, concerns over wildlife conservation have shaped
forest policy and forest management decisions in the United
States in ways that were almost unimaginable two or three
decades ago. Species such as the northern spotted owl and
marbled murrelet in the Pacific Northwest, the red-cockaded
woodpecker in the Southeast, and the Indiana bat in the
Northeast and Midwest were once largely known only to
wildlife enthusiasts, but now drive policy and management
decisions in many forests because of their listing as
threatened or endangered under the federal Endangered
Species Act.
Although the current attention to wildlife and emphasis on
biodiversity in forests has resulted in abrupt changes in
forest management practices, the seeds of change that led
to our current approach to managing wildlife in forests
were planted quite some time ago, and close interactions
between the fields of wildlife and forestry have a rich
history. Until relatively recently much of the attention
that forest managers gave to wildlife in forests focused on
managing habitat for game species and on minimizing impacts
of wildlife on seed production and forest regeneration.
The 1960s and 1970s saw the beginning of a transformation
in our perspectives on wildlife-forestry interactions,
coinciding with increased public awareness of environmental
issues and passage of key legislation such as the
Wilderness Act, the National Environmental Policy Act and
the Endangered Species Act. Concurrent with this new view
was a proliferation of studies on the ecology of wildlife
in forests and enhanced understanding of the importance of
dead wood, riparian habitat, old-growth forests and complex
forest structure for wildlife.
A central paradigm emerging from this research relates to
the concept of spatial scale. A large number of recent
studies have demonstrated that wildlife select different
habitat characteristics at different spatial scales, and
that attention to forest characteristics at different
scales is critical to provide high quality habitat for
wildlife. For example, early attempts to provide habitat
for northern spotted owls emphasized protection of the nest
tree (habitat component scale). We now understand that the
characteristics of the stand in which the nest tree occurs
are also important (stand scale), as is the amount,
distribution and characteristics of stands surrounding the
nest stand (landscape scale) and connectivity among
different nesting areas (regional scale). To effectively
manage for this species, attention to each of these scales
is necessary.
Within forest stands, key aspects of habitat to which
wildlife respond include vertical and horizontal
heterogeneity, amount of standing and fallen dead wood, and
vegetative species diversity. Special habitat features,
such as riparian areas, rocky outcrops and unique plant
associations, also provide important habitat for a number
of species of wildlife. Forest management that maintains or
increases structural complexity within stands can provide
multiple niches for wildlife.
For many species of wildlife, standing dead wood, or snags,
is particularly important. Woodpeckers and a suite of
cavity-nesting birds, bats, forest carnivores, arboreal
rodents, and other species are dependent on or highly
associated with snags. Few management decisions influence
abundance and composition of wildlife communities as
strongly as decisions concerning management of snags.
Maintaining large diameter snags in a variety of stages of
decay is a key management strategy to providing habitat for
several species.
Just as many species have been shown to prefer the complex
forest structure found in old-growth stands, others are
closely associated with stands in early stages of
development. Because of the diversity of habitat needs of
different wildlife species, maintaining a wide array of
stand conditions helps promote a diverse wildlife
community. A good example of an approach to maintain a
variety of structural conditions through time is the recent
management plan developed by the Oregon Department of
Forestry. This plan manages for different structural
conditions spread across the landscape, providing
connectivity between key habitat types. Appropriately,
these plans call for maintaining a minimum amount of
habitat in the stem-exclusion stage, as this developmental
stage tends to be poor quality habitat for most wildlife
species.
While providing the diversity of habitat to meet the needs
of wildlife species can be a daunting task, even simple
steps, such as providing dead wood in forest stands,
managing for a variety of stand conditions, and protection
of special habitat features, can result in significant
benefits for wildlife.
Extracted from:
Society of American Foresters, Western
Forester 49(4) 2004
Wood Decay in Healthy Forests: The Paradox and the
Promise
by Bruce G. Marcot
USDA
Forest Service, Pacific Northwest Research
Station
A Legacy of Snags in the System
It is widely acknowledged that standing dead or partially
dead trees provide important habitat for woodpeckers and
other primary cavity excavators, and that a wide array of
other animals use woodpecker cavities. Guidelines exist for
maintaining or even creating snags on federal lands, state
forest lands and private forest lands. It is also known
that large-diameter snags held over from previous, older
stands constitute one aspect of “wood legacies”
that provide ecological functions more fully than
small-diameter snags produced from understory suppression
during even-age stand management.
Snags are utilized by wildlife in many ways. For example,
red squirrels use witches’ brooms created by
mistletoe in Douglas-fir trees. Black bears den in hollow
trees and logs in northeastern Oregon. Shredded down wood
and bark piles at the base of snags are often used by
salamanders in Douglas-fir forests of Washington.
Long-eared bats use tree stumps for roosts. High-cut stumps
are used by white-headed woodpeckers for cavities.
Ponderosa pine snags are used as breeding roosts by bats.
However, it has only been more recently acknowledged that
many other forms of wood decay—other “wood
decay elements” or WDEs—than just snags also
provide vital ecological services in forest, woodland and
riparian ecosystems. This is a brief review of the
diversity and ecological roles of WDEs.
Beyond
snags: elements and functions of wood decay
elements
WDEs also include down wood, root wads, tree stumps,
litter, duff, broomed or diseased branches, hollow trees
and partially dead trees. They also provide resources and
substrates for many organisms that perform vital ecological
roles of transforming and cycling nutrients, decomposition,
respiration and other biological processes. Such roles
benefit ecosystems far beyond the confines of the wood
decay elements per se, and are a natural and vital part of
native forests and ecosystem processes. Providing for WDEs
may seem like sacrificing growing space, but in the long
run, ecological processes of WDEs greatly contribute to
overall ecosystem health, soil productivity and growth of
desired tree species.
Beyond just providing wildlife habitat, WDEs also provide
for an array of ecological roles of wildlife in forest
ecosystems. For example, in southwest Oregon
conifer-hardwood forests, hollow trees are used by 24
wildlife species, including nine bats, five owls, two
woodpeckers, a swift and others. Of these 24 species, five
(two birds and three mammals) also serve the beneficial
function of dispersing seeds and fruits of native plants,
and two (mammals) tunnel in soil that in turn creates
burrows used by other species and can help improve soil
structure and uptake of organic matter. These and other
secondary beneficial ecosystem services are provided by
many wildlife
species associated with all WDE categories in all forests.
Down wood has a high pore volume and serves as moisture
reservoirs, and in moderation, provides microsites for
beneficial mychorrizal fungi, plants and animals that aid
in forest recovery after prolonged drought or fire. Large
pieces of down wood eventually work into the soil where
they serve as long-term, time-release sources of humus,
organic matter, phosphate and nitrogen, and mediate soil
nutrient cycles. Woody material in the soil creates acidic
soil conditions that favor soil microbial activity that
help fix nitrogen for use by trees. Down wood on the
surface can help stabilize soil movement and deter erosion,
and serve as nurse logs for spruce, hemlock, alder,
Douglas-fir and other trees. Wood that enters the soil
profile tends to stay there. Some carbon dating studies in
the Inland West have shown buried wood material to be 500
to 1,000+ years old. All this means that restoring natural
levels of coarse wood in soil horizons may be an immensely
long-term process.
The
paradox of health and harm
Such direct and indirect benefits of WDEs, however, are
often ignored because of the fear that WDEs (especially
snags and down wood) increase undesirable fire and insect
hazards. In some situations this is true, but the
ecological benefits of WDEs contributing to healthy,
diverse, productive forests over time could be weighed
against any such short-term risks. The challenge to forest
managers is to provide enough WDEs
in a variety of types and spatial patterns for long-term
soil productivity, ecosystem functions, and use and need by
organisms, but at the same time to avoid undue hazards of
fire, insect pest outbreaks, and operational and
recreational safety problems.
The promise of how much, where and how
WDEs could be provided in both clumped and dispersed
patterns, particularly taking advantage of natural patterns
such as small, isolated root rot pockets that create local
clumps of snags and hollow trees, or low-quality trees with
splitting or sloughing bark growing on rocky soil or sites
unfit for commercial tree use. More widely dispersing
rather than clumping WDEs in fire hazard zones, such as
urban-forest interfaces, may provide some measure of wood
decay, but not contribute to fire and insect pest risks.
Also, managing for WDEs can be evaluated at stand, local
watershed and broader landscape scales to ensure that large
areas are not devoid of legacy wood elements. Most
important, by considering WDEs in forest management,
managers are planning for the future when they account for
dynamics of tree growth and decay, stand rotation and
disturbance dynamics (particularly fire, insect pests and
pathogens).
How much WDEs should be provided? That depends, of course,
on the overall forest management objectives. One possible
objective is to provide a minimal amount of WDEs in more
intensive tree farms to help complement greater amounts of
WDEs found on adjacent national forests or other
multiple-use forest lands. Other possible objectives may
include providing greater patches of WDEs on less
productive growing sites, or rotating stand management
methods across the landscape so that each site gets an
occasional infusion of WDE legacies and large wood into the
soil. To various degrees, the forest manager may wish to
emulate some range of historic or unharvested conditions.
In forests of the Inland West, about 30 percent of organic
volume of soils will maintain peak mycorrhizae amounts in
the organic soil horizon. This translates to about 10-15
tons/acre of surface down wood, which should be relatively
large woody residue scattered across areas with minimal
soil disturbance. Chipping of fuel wood is not an
ecologically viable solution, as rainfall leaches large
amounts of toxic, water-soluble phenolics from the chips
and blocks soil structure, causing mortality of tree
seedlings. In some cases, artificial logs could be
introduced to cover greater than 25 percent of the area in
piles large enough to provide deposits of large coarse wood
similar to natural levels.
Broadening
the vision
The overall lesson is that the forest ecosystem manager can
view WDEs as natural and desirable parts of the forest
ecosystem, and more than just providing occasional snags
for woodpeckers. All types of WDEs provide important
functions for plants, animals and ecological processes that
together maintain natural, diverse and self-sustaining
forests.
Extracted from:
Society of American Foresters, Western
Forester 49(4) 2004
Vertebrate Use of Dead Wood in the Pacific
Northwest
by Mark Boyland & Fred L. Bunnell (2002)
University of British Columbia Vancouver, Canada
Abstract:
The
many unique features of dead wood make it attractive as a
place to forage, nest, and shelter. In the Pacific
northwest, 69 vertebrate species commonly use cavities, and
47 species respond positively to down wood. Cavity users
typically represent 25% to 30% of the terrestrial
vertebrate fauna in forests of the Pacific Northwest.
Cavity excavators select for heart rot—major factors
governing it’s presence are tree species, site
productivity, tree age, and time. Data presented shows 2-3
large snags per hectare, and 10-20 smaller snags per
hectare, throughout the rotation, are required to sustain
cavity nesting birds.
Ecosystem Components that Encourage Wildlife
Diversity
Extracted from
Appendix: Wildlife Habitat Relationships, Coast Range
Forests
Publication R6-NR-ECOL-TP-03-02.
USFS Pacific Northwest Region, 200
Dead and partly decomposing
trees
Approximately
one-third of bird and mammal species in forested landscapes
use tree cavities for denning, nesting, or roosting. Snags,
dead tree tops, and otherwise decayed portions of live
trees provide opportunity for woodpeckers and other species
to create holes. These cavities are in turn used by
secondary cavity-nesters that search for and use these
cavities, rather than create their own. Cracks, crevices
and loose bark also provide nesting and roosting substrates
for bats and brown creepers. Probably the rarest structures
in the forest important to vertebrates, and the most
difficult to duplicate, are large hollow trees. These are
often western redcedar or incense cedar, but can be just
about any species of tree. Some trees are hollow from the
bottom up, some from the top down, some only in the middle
(but the latter are very difficult to find). Bears, bats,
swifts, and other mammals and birds utilize these
structures. Vaux’s swifts nesting in forests
exclusively use these structures.
Down wood
Logs
are used by a wide variety of wildlife, but small mammals
and amphibians are probably the groups most dependent upon
these structures. Some species prefer more sound
structures, utilizing the space created by loose bark,
while others predominate in more decayed structures that
are soft enough to tunnel through or that have a matrix of
navigable cracks due to the work of brown cubical rot. Many
species utilize logs simply for hiding cover, nesting
cover, travelways, or perches.
Diversity of tree species
Different
tree species germinate in different ground conditions, grow
at different rates, exhibit different shapes to their
crowns, boles, and leaves, have different susceptibilities
to root rots, stem rots, and mistletoes, are differentially
resistant to stem breakage from wind, ice, and snow,
attract or repel different communities of invertebrates,
and finally, different tree species have different maximum
heights and senesce and die at different ages. All these
differences suggest that a wide variety of nesting,
foraging, roosting, hiding, and resting habitats may be
produced by different combinations of species, ages, and
conditions of trees. Thus, single-species stands typically
exhibit less vertebrate diversity than multi-species
stands.
Broadleaf trees
The
significant differences between conifers and broadleaf
trees cause the combination of these species in forest
stands and landscapes to significantly increase the number
of animal species present. Warbling vireos are most
frequent in areas with abundant broadleaf trees or tall
shrubs, and black-throated gray warblers and black-headed
grosbeaks prefer mixed habitats. In the Douglas-fir and
drier western hemlock associations on the eastern
foothills, broadleaf trees (especially oak) attract western
gray squirrels, but in all plant associations, sites
dominated by broadleaf trees are likely absent of Douglas
squirrels. Broadleaf trees may be important to mollusk
diversity.
Shrubs
Forest
understory shrubs provide nesting structures for
Swainson’s thrushes, winter wrens, and Wilson’s
warblers. The Wilson’s warbler in particular utilizes
tall deciduous shrubs for nesting. Shrubs provide important
habitat for invertebrates, browse for deer and elk, and
cover for a wide variety of birds, mammals, and reptiles.
Patches of older shrubs in particular can be hotspots for
arthropod, lichen, and bryophyte diversity.
Fruits, berries, and nuts
Numerous
trees, shrubs, and forbs produce seeds and soft fruits that
are consumed by a wide variety of birds and mammals. Some
of the more common species producing mast include all
conifers, maples, and hazel. Oregon white oak and Pacific
madrone occur sparingly, most often in or near the
Douglas-fir series. Species producing berries (i.e. seeds
with a fleshy outer layer) include dwarf and tall Oregon
grapes, salal, several species of blackberry, thimbleberry,
several species of manzanita, salmonberry, bitter cherry,
snowberry, several species of rose, Pacific dogwood,
several species of huckleberry, blue and red elderberry,
and cascara.
Soil and forest litter
Soil
characteristics combine with annual temperature,
precipitation, and solar exposure to determine suitability
and growth potential of a site for plant species and
communities. Burrowing animals such as gophers, moles, some
voles, and mountain beaver prefer relatively porous soil.
Several species of shrews appear to be particularly
abundant where forest floor litter is abundant and deep,
and western red-backed voles are especially common in areas
with a thick duff layer. Forest floor characteristics are
also important to ground-dwelling invertebrate communities.
Rocks, cliffs, caves
Many
different structures are created by rock. Cobble-sized
talus is common below cliffs and on steep rocky slopes.
These habitats may be dominated by several species of
amphibians (e.g. western redback salamander, clouded
salamander) if wet, and several species of snakes (e.g.
northwestern garter snake) and lizards (e.g. northern
alligator lizard) if dry, and some communities have both.
Mice and voles also inhabit talus. Accumulations of larger
rocks provide homes for long-tailed weasels and potential
denning sites for other medium to large mammals. Cliffs
provide nest sites for peregrine falcons, common ravens,
and violet-green swallows, and caves are often home to
turkey vultures, bats, and medium and large mammals. In
arid associations, seepy areas provide rare habitats for
amphibians and mollusks.
Water
While
many animals gain a substantial portion of their water
needs from the food they eat, most also require consumption
of water on a near-daily basis. While small mammals and
birds can often obtain water from condensation on
vegetation, larger animals are more dependent upon more
substantial water sources such as streams and ponds. These
undoubtedly provide the predominant water source for the
majority of birds and mammals in most landscapes. Even
migratory birds, presumably unfamiliar with any particular
small stream, have an uncanny ability to locate small
trickles and pools located on an otherwise dry stream
segment under a tall forest canopy.
Streams
Pacific
and Cope’s giant salamanders, Columbia and southern
torrent salamanders, and tailed frogs are restricted to
breeding in cool, running water. The most common of these,
the Pacific Giant Salamander, contributes significantly to
the biomass and predation within small streams. While
terrestrial densities of stream-breeding amphibians
decrease with distance from streams, and relatively high
rainfall and forest floor humidity gives more freedom for
terrestrial travel in western Coast Range forests.
Ponds
Western
toad, Pacific tree frog, red-legged frog, bull frog,
northwestern salamander, long-toed salamander, and
rough-skinned newt are restricted to breeding in still or
very slow-moving water. Highest terrestrial densities of
these species are found in close proximity to breeding
sites, and sometimes concentrate on particular hillsides or
along particular inflowing or outflowing streams. Some
species exhibit substantial dispersal capabilities and may
be found in very small numbers several miles from any
suitable breeding habitat. While most species typically
breed in ponds or lakes, others (e.g. Pacific tree frog)
will sometimes breed in very small water, even puddles in
abandoned roads, and roadside ditches in open roads. Some
require semi-permanent water; for example, northwestern
salamanders require more than one season to metamorphose,
and may even become neotenic (a permanent
“larval” form that is capable of reproduction),
while others (e.g. Pacific tree frog) can breed in water
that dries up during summer, because they metamorphose
rapidly. Some (e.g. northwestern salamander, red-legged
frog) require substrate such as sedges or woody plant stems
for egg-laying, while others (e.g. Pacific tree frog,
rough-skinned newt) do not require such substrate, though
the newt may have requirements for pond-bottom composition.
The marsh shrew and wood duck
are common inhabitants of ponds as well as small streamside
wetlands. Common garter snakes in particular are attracted
to ponds containing frog tadpoles. Marsh shrews also take
advantage of this abundant food source. Vaux’s
swifts, common nighthawks, and several species of swallows
and bats obtain water in flight at ponds and still water
pools in streams and rivers. These species also forage on
flying insects over these waters.