THE
SUCCESSIONAL ECOSYSTEM
Nature,
it is said, abhors a vacuum. Where there is nothing, there is certainly
something keeping it that way. This is true of the ecosystems around
us. Humans keep systems artificially empty, or at least very simple,
as we do in agricultural fields and lawns. However, if such simple
systems are not kept so artificially, nature invades and a more natural
circumstance prevails. In Northeast Ohio, one can see this happening
everywhere. The dominant native vegetation of this area can be described
as deciduous forest. Such a woodland is found, however, only in tracts
of land which have remained undisturbed for a number of years. Such
primeval forests covered much of Ohio at the time of European conquest,
having remained undisturbed since our climate stabilized after the
glaciers melted ten to twelve thousand years ago. Even the Native Americans
who began farming in the forests of Eastern North America had little
effect on these extensive woodlands. It took the Europeans with steel
axes, beasts of burden, and later internal combustion-driven tractors
to almost entirely clear most of the arable land in the East.
Much
of the cleared land has remained artificially simplified as corn and
wheat fields, lawns, and cities. Some of it, however, has begun to
fill back in, because much of the arable land is now fallow. Farms
have been abandoned, land has been exhausted, and more efficient farming
tools and chemicals have reduced the amount of land needed to be tilled.
This land has begun to revert to its natural ecosystem, and has done
so through the process of "Ecological Succession". This regular replacement
of plant communities can be seen all around you. Old fields of grasses
and herbs are replaced by shrubs and brambles. Small trees grow into
large ones which are replaced by other species, until a special thing
happens. The successional process slows and stabilizes. A point has
been reached, called ecological climax, at which the whole ecosystem
becomes self-reproductive. At that point, an ecosystem, if left undisturbed,
will stabilize, and for year after year will change very little. Dominant
plant and animal species will be roughly the same, and the young plants
and animals which are present are much the same as the surrounding
mature species.
In some
areas of the world, the stable climax is a jungle, in others a cactus-dotted
desert, in this area a deciduous forest. This woodland part of the Wayne
College Nature Trail (in 1994) is a mid-to-late-successional woodland.
It is dominated by black cherry (Prunus serotina) and black locust (Robinia
pseudo-acacia) trees. Other trees such as sugar maple (Acer saccharum)
and ashes (Fraxinus spp.) are seen only as saplings at this point. What
this means is that trees such as the cherries and locust are being succeeded
by the maples and ashes and will eventually be out competed and replaced
by them. If not disturbed, by the middle of the twenty-first century, this
area will have stabilized into a maple-dominated woodlands, a common pattern
seen in eastern North America. So, observe this woodland as it changes
over the years and look for the same sorts of changes in undisturbed areas
around you as nature fills a vacuum.
-------Forrest
J. Smith
-------Professor
of Biology
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