Forest Succession: Maturing into Forest
What kind of forest greeted the first settlers
to our region? We like to think of North America before European
settlement as a vast expanse of unbroken forest, but the truth is that
forests have been pushed, chopped, frozen, or burned down as long as
they have existed. Every time, the forest eventually
regrows. Sometimes the regrowth is slow --- if an entire hillside
sloughs off in a mudslide, the bare rock that is revealed may take
thousands of years to turn back into forest. On the other hand,
if a single tree dies from insects or disease, the surrounding forest
may close up the gap in just a few years.
The south half
of the Loop Trail is a perfect example of what scientists call forest
succession --- the stages that an ecosystem goes through as it regrows
a mature forest after some type of disturbance. In this case, the
original forest was wiped out by centuries of farming, remnants of
which are seen in the mature apple and pear trees which line the peak
of Sugar Hill.
Once the
farmers left the land to its own devices for a few years, nature
quickly began to take over. This first step in forest succession
is called the old field stage and is visible just south of the
Frenchman's settlement along the Loop Trail. Ankle to shoulder
high plants abound in the old field stage, and most of the earliest
ones have wind-dispersed seeds. The most common examples are
thistles and milkweeds which produce light seeds with hairlike
projections, well-adapted for catching a breeze and wafting for a few
feet or a few miles.
The growth of
thistles and milkweeds provided protective cover, quickly attracting
birds to the old field. Like wind, birds are another vector for
the spread of old field plants, leaving behind seeds of species like
Pokeweed when they defecate. These bird-dispersed plants produce
tasty berries as an inducement for their avian friends to spread the
plants' seeds into new habitats. Other plants, like burdock, grow
seeds covered with little hooks that catch in the fur of passing
animals, hitchhiking to a new spot.
Milkweeds,
thistles, Pokeweed, and burdock maintain their dominance of the old
field for only a few years in nature before they have built up enough
organic matter in the soil to allow wind-dispersed tree seedlings to
gain a foothold. The first trees to enter an old field in our
area are often Box-Elder, Red Maple, Eastern Red Cedar, and
Tulip-tree. Without the frequent mowing which maintains the
fields on Sugar Hill, young trees would smother out most of the old
field herbs within a decade. The dense thicket that forms is
often full of thorny shrubs like Multiflora Rose and blackberries and
is known as early successional forest. Native Americans often
burned forests to produce these thickets since they house and feed game
animals and are often full of plants edible to humans as well.
Just as the old
field herbs enriched the soil to allow early successional trees to
grow, the early successional trees lay the groundwork for their own
demise. Another decade or two may pass before the Red Maples and
Tulip-trees form a dense canopy, but once they do their sun-loving
seeds are no longer able to germinate. Instead, magnolias, Beech, and
other trees begin to sprout in the dense shade on the forest
floor. These trees are the first signs of what scientists call
the climax forest --- the type of plant community that will live in an
area in the absence of disturbance. The cove hardwood
forest discussed in the last chapter is one of the climax forest
types that can be found on Sugar Hill.
After a few
hundred years, the forest has hit its stride. The rabbits and
meadowlarks that hid in the old field and early successional forest
have given way to Pileated Woodpeckers that hunt for grubs in standing
dead snags and Black Bears that curl up on winter nights inside hollow
trees. Trees have aged and range in size from saplings to
behemoths. Some have fallen over, leaving behind logs that host
mosses, voles, and salamanders. None of Sugar Hill has quite
reached this stage --- which is commonly known as old growth --- but
the hill above Oxbow Lake comes close.
And then little
disasters strike. A tree is blown over and takes down dozens of
its neighbors, opening up a treefall gap --- a sunlit opening in the
forest. If the gap is large enough, a little field forms, full of
milkweed and burdock, then young Tulip-trees, then Beeches and
magnolias, and the cycle continues.
Want
to be notified when new comments are posted on this page? Click on the
RSS button after you add a comment to subscribe to the comment feed.
