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Explanation: It
was a massive conflagration. Two huge forest fires -- started by
lightening strikes in the dry forests of interior eastern Oregon -- had
merged. The forest was already parched from scant summer rain, and many
trees were made into tinderboxes by beetles. Malheur National Forest and
the State of Oregon had their hands full, battling this one. With fires
this big, firefighters are often recruited
from across the country. So,
after the smoke cleared -- literally -- what became of the land? How
could the forest ever rejuvenate itself? The
answer lies in very subtle clues. This fire occurred in August 1996, and
just a couple years later I found myself studying invertebrates and soil
conditions, and inspecting the life that arose and persisted ... after the
burn. Here is what I found.
The answer to the old children's
riddle, "What travels uphill
faster than downhill?" is ... fire.
Often, upper slopes and ridgeline, such as the one shown
above as part of this fire complex, are most affected
and often suffer crown fires that spread through the forest canopy.
But ... also notice the green trees that escaped the blaze,
scattered individually or in clumps. These are one major source
of forest rejuvenation.
Some 42% of the Tower Fire, which eventually covered
approximately 20,000 acres, was hot enough to kill most of
the trees in the stands it encountered ... but this means that
58% of the fire left behind live, viable trees.
Further,
some trees of this dry forest region are adapted to
needing occasional fire for their cones to open and seeds
to be released and germinate.
Very hot fires can scorch the soil, but less severe "surface
burns" can also
serve to release nutrients. Note the charred snags (standing dead trees)
in the
background, but also the vigorously-growing shrubs and tree seedlings
in the foreground.
This is a typical patchy pattern of such
fires, where local
topography and vagaries of wind can cause
specific locations to burn hot, burn cool, or
escape the blaze and become a source of recovery.
Here is one of the unsung heroes of forest regeneration after the burn.
Millipedes
are comminutors and detritovores, that is, they seek out
and chew up decaying organic matter, thereby serving
the key ecological function of recycling soil nutrients.
They also burrow in the ground, helping to mix in
organic material.
Further signs of life -- big life! These are elk pellets.
As elk wander, browsing on newly-sprouting shrubs
and defecating as they travel, they spread
nutrients, organic matter, and even
viable seeds throughout
the forest ... helping to regenerate vegetation after the burn.
More signs of life ... not a burrow, but a cache site, likely
made by a ground squirrel hiding seeds for a later lunch.
Sometimes they forget their hiding sites, or have no need
to return, thereby essentially planting the seeds for restoration.
Here
is a colony of carpenter ants (Camponotus sp.) working to break down
the structure and chemistry of logs and other dead wood. They
do not eat the wood as do termites, but they create intricate tunnel galleries
in the wood for their colonies, thereby helping to disintegrate the fibers and
recycle the nutrients back into the soil. Often,
they do their burrowing after fungi has first softened the wood -- a sort of
micro-forest succession in itself in every log.
And here is the result of the carpenter ants' work: frass.
Frass is the fine shavings produced by chewed wood,
sometimes as find as sawdust. If it happens in your home, it's
a big pest problem. But in the forest, it's part of the
ecological recovery and recycling process.
More
sign of life ...
woodpecker feeding cavities
in the base of a fire-charred
Ponderosa pine tree. Such cavities can serve as introduction
points for wood fungi and beetles and other
insects that consume the wood,
again helping in the recycling functions. Some studies
have even shown that
fungi can be carried on woodpeckers'
beaks, thus serving to transfer
fungi from tree to tree.
My able field assistant installing pit-fall insect traps
during my study.
From such research, we can learn not just
more about the
ecology of life after fires, but also how best to let forests
recover themselves with life after the burn.
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