Oaks and Fire
In recent decades, scientists have begun to
realize that fire --- like masting --- is an
essential part of the oak-hickory
community. The exact role of fire, though, has been roundly
debated. Scientists agree that before humans arrived in North
America, many ecosystems naturally burned when lightning ignited dead
plant matter like fallen logs or dried grasses. Once Native
Americans reached the continent, they accelerated the burning process
in many areas, starting wildfires to open up forests for agricultural
land, to promote the growth of edible plants like blueberries, and to
provide browse for game animals like deer. Then Europeans
arrived, and for a while the fires were tremendous. Some fires
were set purposefully for many of the same reasons Native Americans had
burned the land, while other fires were set accidentally.
As our
settlements encroached further and further into the forest, we entered
an era of fire suppression. Smoky the Bear warned us that “Only
you can prevent forest fires”, and we took the message to heart.
Not only were people more careful of their own fires, we began to put
out naturally occurring fires. Fire was --- and is --- dangerous
when it laps up against barns and houses. It seemed better,
safer, to just to quench the flames whenever they occurred.
In some areas,
fire suppression was not a big deal. In moist coves here in the
mountains, scientists suspect that non-human fires would naturally burn
once or twice a century, or even less often. Fallen branches and
trees quickly rot in our moist, humid climate, turning into rich soil
for salamanders and millipedes to wander through. Out West,
though, fire suppression is another matter entirely.
Many dry
ecosystems, like pine forests, depend on fires to stay in
business. When left to their own devices, these woods might burn
every couple of years, killing out encroaching hardwoods and opening up
the canopy for sun-loving pine seeds to germinate. Without fire,
some pines cannot reproduce at all --- the Table Mountain Pine, which
can be found around here on extremely dry ridges, keeps its cones
closed tightly around the seeds until fires come through to melt the
cones open, releasing the seeds to germinate in the rich ash left
behind. In the western United States, many more species depend on
frequent fires to release their seeds and sprout.
Ecologists
warned us that we were getting in deep water by suppressing the natural
fires in these ecosystems, but most of us were not interested in a pine
tree that was unable to reproduce. We started perking up our
ears, though, when the fire suppression tactics hit us in the
wallets. Western forests are far drier than our Appalachian
mountain woods, and when western trees fall to the ground, they are
extremely slow to decay. Without frequent fires to break the
debris down, the forests became choked with bone dry wood, just waiting
to ignite. When lightning finally struck, or a campfire swept out
of control, the wildfires ravaged the countryside like never
before. Before fire suppression, frequent fires cleaned up the
debris at regular intervals, so fires tended to run through western
forests fast and cool, seldom licking up into the tops of trees or
doing real damage to anything except seedlings.
Post-fire-suppression fires, though, raged as if the forests had been
doused with lighter fluid. The flames leaped up into the canopies
of the trees, racing and ravaging through the forests and into the
suburbs. You have probably heard about the devastating California
fires of the last few years --- these fires are largely due to decades
of suppressing every natural fire that came along.
Which brings us
back to the oak-hickory forest. Oaks are not quite as dependent
on fire as pine communities are, but scientists are beginning to
realize that fire has boosted their abundance. Most acorns will
not germinate in the shade, so they depend on some kind of disturbance
to open up the canopy and give them a little sunlight in which to
grow. Without frequent fires, most oak communities in the eastern
United States are slowly turning into other types of forests.
Around here, cove hardwood forests are advancing up the hillsides,
slipping between aging oaks as the moisture-loving trees grow toward
the canopy. Without fire, our oak forests may disappear from
everywhere except the driest ridges within the next century or two.
Some land
managers are fighting back using prescribed burns --- intentionally lit
fires that can be controlled to run quickly across the forest floor,
mimicking the natural process of lightning-ignited fires. In
western States and in the pine forests near the Gulf coast, these
prescribed burns seem to be doing a good job of keeping the natural
ecosystems in balance while preventing devastating wildfires. In
oak forests, though, prescribed burns lead to more questions than
answers.
Remember how I
said that Native Americans set fires intentionally for thousands of
years before European settlers arrived in North America?
Palaeontological evidence suggests that our oak-hickory forests --- now
so widespread --- followed in the footsteps of the fires lit by Native
Americans, and later by European settlers. The reason our oak
forests are beginning to fade away is that, in most parts of our
mountains, oak forests are essentially man-made. Should we be
maintaining an ecosystem that would not occur over much of its range
without the help of people? On the other hand, if we let the oak
forests fade back to their natural obscurity, will we lose plants and
animals that evolved to live in these man-made oak forests?
The
relationship between humans, oaks, and fire is a tricky one that brings
us to a difficult question --- what exactly is natural? Like most
difficult questions, there is no single right answer. Short of
packing up every human being in North America and shipping us overseas,
we have to learn to coexist with our ecosystem, to compromise between
our needs and the needs of the natural world.
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