Let us Praise—and Keep—the Dead

*Dead.* Most of us have negative associations with the word. After all
how did Death Valley get its name? Not because it was a favorite
vacation spot for prospectors. Is anyone interested in fishing the
Dead Sea? And when we say someone looks like “death warmed over,” it’s
not usually taken as a compliment. So it’s not surprising that most of
us tend to view dead things as undesirable, unless we are talking
about mosquitoes and rattlesnakes.

We impose this cultural bias about dead things to our forests as well.
Public land management agencies spend billions annually trying to
contain wildfire and insect outbreaks based upon the presumption that
these natural processes are destroying the forest by killing trees.
Even though there is now some grudging acceptance by land managers
that wildfires and insect attacks may be potentially beneficial if
they do not kill too many trees, stand-replacement fires, ice storms
and large beetle outbreaks are still viewed as unnatural and
abnormal—something to suppress, slow and control.

When these natural processes kill trees, managers propose logging to
“salvage” the economic value of the downed trees. They operate on the
tacit assumption that surplus wood can be removed without hurting the
forest’s ecosystem, and until now that has formed the basis of
scientific and/or sustainable forestry.

But a new perspective is slowly taking root among forest managers,
based on growing evidence that forest ecosystems have no waste or
harvestable surplus. Rather, it seems that forests reinvest their
biological capital back into the ecosystem, and removal of
wood—whether dead or alive—can lead to biological impoverishment.
Large stand-replacement blazes and major insect outbreaks may be the
ecological analogue to the forest ecosystem as the hundred-year flood
is to a river. Such natural events are critical to shaping ecosystem
function and processes. Scientists are discovering that dead trees and
downed wood play an important role in ecosystems by providing wildlife
habitat, cycling nutrients, aiding plant regeneration, decreasing
erosion and influencing drainage, soil moisture and carbon storage.

“When you start to look at western forests outside of wildernesses and
parks, you notice right away that they lack large quantities of downed
wood—dead trees,” says Jon Rhodes, an independent consulting
hydrologist in Oregon. “Ecologically speaking, there is a big
difference between areas that have been logged compared to areas that
are left alone.”

Chad Hanson, a University of California, Davis, researcher, agrees.
“We are trapped by an outdated cultural idea that a healthy forest is
one with nothing but green trees. An ecologically healthy forest has
dead trees, broken tops and downed logs.” Such forests may not look
tidy from the perception of a forester, he says, but it’s an
indication that the forest is healthy and biologically diverse. “Pound
for pound, ton for ton, there is probably no more important habitat
element in western conifer forests than large snags and large downed
logs,” Hanson says.

Studies have consistently concluded that most western forests have a
deficit of large snags and downed dead wood. “Large standing trees are
important,” Rhodes says, “but they shouldn’t be museum pieces. They
should be part of functioning ecosystems.” When old-growth trees burn
in wildfires, they aren’t completely lost, he says, but provide the
ecosystem with large quantities of snags and downed wood. “While some
say we can’t afford to have old growth burned by fire, it’s apparent
that we can’t afford for old growth not to burn in fires, due to the
importance of large snags and downed wood and its current lack in
western forests,” he says.

Writing in a 2004 article in /Conservation Biology,/ University of
Montana ecologist Richard Hutto sums up the new thinking about the
ecological value of dead trees. “I am hard-pressed to find any other
example in wildlife biology where the effect of a particular land-use
activity is as close to 100 percent negative as the typical post-fire
salvage-logging operation tends to be,” he wrote. “Everything from the
system of fire-regime classification, to a preoccupation with the
destructive aspects of fire, to the misapplication of snag-management
guidelines have led us to ignore the obvious: we need to retain the
very elements that give rise to much of the biological uniqueness of a
burned forest—the standing dead trees.”

*Healthy Dependence*

Dead trees are important to wildlife. Think woodpeckers. But many
other species depend on dead trees and downed wood for food and
shelter.

Hutto reports that upwards of 60 percent of species that nest in
severely burned forests use only snags for nest sites. In addition,
about 45 percent of all North American native bird species rely on
snags for at least a portion of their life cycle.

Hutto has found fifteen species that are most abundant in forests with
high numbers of snags resulting from high-intensity stand-replacement
crown fire—the kind of fires that foresters pejoratively call
catastrophic. Hutto notes it is doubtful that these species would have
evolved such dependency on snag abundance if large stand-replacement
fires and widespread insect outbreaks were uncommon or unnatural, as
some suggest.

But it’s not just the use of snags for nesting, or even feeding as
with woodpeckers, that attracts birds and other wildlife to recently
killed forests. Burned forests also are used extensively by
seed-eating species that are attracted by the abundance of new seeds
shed by cones and colonizing plants.

Even the presumption that large blazes are a threat to spotted owls is
being challenged. “There are several studies which indicate that
spotted owls actually benefit from substantial patches of
high-severity fire within their home ranges,” says researcher Hanson.
“They selectively forage in unlogged, high-severity burn patches.”
However, he adds, if these burned areas are salvage logged, spotted
owls avoid them.

In a paper presented at a conference on the ecology and management of
dead wood in western forests, researcher Timothy Kent Brown estimated
that two-thirds of all wildlife species use dead trees or downed wood
during some portion of their life cycle. Among Pacific Northwest
vertebrates, sixty-nine species depend upon cavities for shelter or
nesting, while forty-seven other species are strongly associated with
downed wood. And it’s not just the obvious species like woodpeckers
that demonstrate this dependence. Many bat species, for instance, hide
in cavities in dead trees or under the loose bark of dead and/or dying
trees.

Jim Andrews, a professor at Middlebury College in Vermont, studies
amphibians and reptiles in northeastern forests. “Foresters tend to
look at the forest from the floor up,” he says. “I have occasionally
gone on field trips with them, and they were rather proud of how they
had managed their forests, but the forest has nothing in it. There’s
no cover. No places to find live critters.”

Andrews notes that dead and dying trees are important for many
cold-blooded species, from gray frogs to arboreal rat snakes.
“Standing snags, once they get big enough so that they have hollow
centers—what foresters call ‘overmature’…are the places where wildlife
reside,” Andrews says. “To a biologist you don’t have overmature
trees—you have wildlife habitat.”

Andrews notes that the greatest biomass of terrestrial vertebrate
species found in eastern forests are salamanders, not the more
charismatic large mammals like deer and moose. Salamanders provide
food to many other species, from wild turkeys to shrews.

But salamanders are also significant predators in their own right,
Andrews says. They eat beetle larvae, fly larvae, ground beetles,
spiders, sow bugs, round worms and other invertebrates that feed on
forest debris. In doing so, they shape the forest ecosystem much as
wolves do on another scale. “Salamanders, by preying upon these
species that consume leaf litter, help to maintain a deeper layer of
leaves and other organic debris that holds moisture, reduces floods
and that kind of stuff,” Andrews says.

*SMALL BUT CRUCIAL*

It’s easy to identify an ecosystem for its most photogenic species,
but there are dozens of small cogs that are of equal importance. One
of those is ants, and downed logs are their preferred home. Ants are
among the most common invertebrate in forest ecosystems and, not
surprisingly given their abundance, are critical elements in forest
ecosystems.

The most obvious value of ants is as food—from birds such as flickers
to much larger animals like bears. In fact, research suggests that
ants are among the most important food for bears in Oregon during June
and July, as well as later in the summer if the berry crop is small. A
British Columbia study found that grizzly bears rely on ants for food
late in the fall when berries are unavailable. Reducing the number of
dead trees, and thus ants, has a direct consequence for bear survival.

But ants also prey on insects that attack trees. For example, studies
in Washington and Oregon discovered that ants accounted for an 85
percent reduction of pupae from two tree-defoliating moths.

Dead logs and snags are also home to pollinating insects. Solitary and
colonial bees, of which there are hundreds of species that reside in
downed logs and/or snags, are among the major pollinators of flowers
and berry-producing shrubs.

Dead trees are even important for other plant species. Bureau of Land
Management botanist and lichen expert, Roger Rosentreter, says that
dead snags, by creating suitable habitat for lichen growth, carry the
legacy of lichen species to the next generation of live trees in the
forest. Research by Oregon State University professor Bruce McCune
found that some common lichens were more abundant on barkless branches
of dead trees than on live ones.

Healthy forest soils also require decomposing material. Below the
litter layer in the soil is yet another layer of life that depends on
dead wood. “There’s a whole complex food web in the soil that is a
combination of bacteria, fungi, protozoa, micro-fauna like arthropods,
springtails, mites—all those organisms thrive and are important to the
composition of the forest,” says soils specialist Tom Deluca, a forest
scientist at the Wilderness Society’s Northern Rockies office.

Deluca notes that while forest litter, such as fallen needles and
branches, is important to forest soils, forest soil development is
also “very dependent upon the influx of carbon from [whole] trees that
have a life cycle of hundreds of years.”

If the carbon influx (dead trees) created after a wildfire or beetle
outbreak are removed, he says, the soil is robbed of energy for
micro-organisms. “The organic influx is essential to micro-community,”
he says.

*MICRO-SITES*

People commonly assume that wildfire destroys trees and leaves a
smoldering pile of ashes. In truth, some live trees and a lot of dead
wood physically survive blazes. Beyond the value of dead trees as
feeding, hiding and resting habitat for wildlife, downed logs play an
important role in forest regeneration.

Snags and downed logs modify micro-sites that can affect seedling
establishment. For instance, snags provide some shade and reduction of
drying winds, creating more favorable conditions for tree seedling
survival. Researching the effects of fires on snags in Wyoming, Dan
Tinker, of the University of Wyoming, found that only 8 percent of the
downed wood was consumed in fires. He also says that 35 percent of the
downed wood in clear-cuts was a biological legacy left by past fires
that occurred prior to logging. Tinker and his associates found that
these legacy trees intercepted precipitation and funneled it to the
ends of the log, creating a moister micro-site that was often more
favorable for tree seedling germination and survival.

Other researchers have found that, when it comes to trees, all death
is not equal. How a tree dies affects its ultimate role in the forest
ecosystem. A tree killed by bark beetles has a different decay
trajectory than, say, a tree dying from disease or wildfire. For
instance, bark beetles, by breeching the outer bark of a tree, create
tiny openings that allow fungi and other insects to enter the tree’s
core.

Bark beetles emit pheromones that not only attract other bark beetles
but also insects that prey on bark beetles. And the volatiles released
from the decomposing trees attract another entirely different group of
organisms that feed upon dead wood. That is why one researcher in
Europe found that bark beetle outbreaks increased biodiversity in
forest ecosystems.

William Laudenslayer, a U.S. Forest Service researcher at the Pacific
Southwest Forest and Range Experimental Station, and his colleagues
experimentally girdled trees to kill them, a common forestry practice
used to produce snags for wildlife. They compared those snags to trees
killed by bark beetles. They found that “bark beetle-killed trees
provided significantly greater woodpecker feeding activity, cavity
building and insect diversity” compared to snags created by girdling.

Trees heated and killed by fire create sapwood that resists rotting
and lasts longer in the ecosystem. Trees dead prior to the fire tend
to become blackened and charred. Charred trees are also resistant to
decay. Thus, a wildfire creates long-lasting biological legacies that
can survive for a century or more.

*DEAD IN THE WATER*

Wayne Minshall, professor of ecology with the Stream Ecology Center in
the Department of Biological Sciences at Idaho State University,
points out the importance of logs to aquatic ecosystems as well.
“Wherever the logs occur, they cause the stream to meander or braid.
And whenever you get braiding or meandering, you’re getting a
reduction in the power of the stream and delivering the water in a way
so as to dissipate that energy so the flow becomes less destructive.
That’s important in keeping streams healthy.”

Wildfires and/or insect outbreaks create downed logs that fall into
streams and across slopes. Downed logs, by slowing the velocity of the
water, allow sediment to settle out and help return sediment flows to
pre-burn levels. Minshall points out that while organisms have evolved
to deal with episodic sediment flush events, such as those occurring
immediately after a wildfire, they are unable to cope with
forestry-induced sedimentation. To these organisms, a forest fire is
no big deal, he says. “We get a short few years of sediment runoff,
but it’s not a major thing that organisms can’t handle.” But aquatic
organisms can’t take unexpected events they haven’t evolved with, such
as the presence of fine sediment all year round for extended periods
of time. “If we clear-cut, salvage log or put roads in, then the
sediment flows tend towards chronic, and it’s a major detriment to
organisms,” he says.

Rhodes says that scientists have not identified an upper threshold of
logs in streams that is too much for fish. “The more wood, the more
fish, all things being equal,” he says. “Lots of wood is a big part of
the productivity for streams.” The loss of salmonids in many parts of
the West, he says, can be attributed to the absence of wood in
streams.

The criteria for healthy ecosystems can’t be easily defined or
exhaustively listed. But healthy ecosystems have a full array of
processes operating unimpaired, including hydrologic function, soil
productivity, carbon sequestering, provision of wildlife habitats and
keystone disturbances such as fires, floods, storms and insect
outbreaks.

One crucial element present in unmanaged, healthy systems is a
significant amount of dead trees and downed wood, Rhodes says. “There
is seldom too much dead wood in forests and certainly not in unmanaged
ones. However, there is almost always a dearth of it in managed
forests.”

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