 |
|
CASH Courier >
2007
Fall Issue
Selected Articles from our
newsletter
The C.A.S.H. Courier
ARTICLE from the Summer 2007 Issue
Succession: Landscapes In Progress Understanding How Wildlife Management Destroys Ecosystems
Game managers routinely disrupt natural ecological
succession for the purpose of providing target animals for hunters and
trappers.
By John Eberhart
Knowledge of succession (also called natural succession, ecological
succession) is essential for understanding forestry, land use, and game
management.
Game managers artificially boost numbers of target animals (“game” and
“furbearers”) for their customers and political constituents: hunters and
trappers. Interfering with nature’s process of succession is an aspect of
habitat manipulation. Game managers ply an environmentally destructive
pseudo-science, probably harming nature as much as the hordes of legal and
illegal hunters and trappers. In order to understand habitat manipulation,
it is necessary first to know how succession operates naturally.
Succession is the stepwise, gradual, generally plant-dominated,
replacement of one set of plant and animal species (natural community) by
another set until a final steady state, or climax, community is established
and succession ceases. Each plant community is a distinct living-space for
an animal community thriving within. As plant communities change, so do the
animal communities.
Making a succession chart for your locality is interesting and valuable.
Every plant species specializes somewhat. Each lives in a particular
habitat and flourishes under a certain combination of climate, soil, and
water conditions. At a new site, seeds of several plant species are likely
to be present. A community of several plant species (pioneers) colonizes the
site. In time most communities change the quality of the site, making it
less suitable for them. Example: Leaf fall may increase soil fertility.
Plant species that couldn’t live at the site before may move in now and
out-compete their predecessors. Shade may increase until seedlings can’t
grow. Such changes propel plant communities and the soils they inhabit
through a series of stages. Changes are fast initially but slow to an
imperceptible rate at climax.
Plant life in most places is not static. Go back to a field years later,
and an expanse of goldenrods has been replaced by a pine stand. Return to a
beaver pond to find it has silted up and become a meadow. Succession
happens: communities replace one another in an ordered way. With enough time
and without major disturbance, succession ends in the natural, biotic
climax. The climax community is the stable end stage that can perpetuate
itself within the site’s environmental conditions.
The entire sequence of stages is called a sere. Each community within a
sere is a seral (or successional) stage. A succession that starts in
well-drained, moderately moist soil is a mesosere; in usually dry soil, a
xerosere; and a succession that begins in water or poorly drained soil is a
hydrosere.
There are two general types of succession. In primary succession, a
pioneer community sets itself up on a substrate for the first time, no
organisms having lived there previously. Succession on newly formed coastal
dunes, spoil banks, road cuts, cliff faces, talus, glacial till, peat
deposits, gully sides, shallow lake bottoms, sandbars, and river deltas, is
primary succession. Newer communities follow, each of which is more
intermediate in its moisture requirements than the preceding community.
Within climatic limits, succeeding communities beginning on wet sites live
on ever drier sites. Succeeding communities starting in dry environments
live on progressively wetter sites. The climax community is neither wet nor
dry, but moist (mesic).
In secondary succession, vegetation has occupied the substrate in the
past. Some disturbance has partly or entirely killed or removed the
community that was there, exposing a soil that has already progressed
somewhat toward maturity. Such plant destruction may be natural (e.g.,
windthrow, wildfire, flood) or human-caused (e.g., burning, grazing
livestock, tillage, draining, logging, bulldozing, climate change). The
secondary plant community series following a change in the original
vegetation usually differs from the primary successional series. A
plagioclimax is a stable community arising from a succession that human
activity has inhibited or deflected, directly or indirectly. In an arrested
succession, the stable community is a naturally occurring seral stage and it
should be possible for succession to continue once the disturbing force has
stopped. Example: Mowing a lawn sets back the “clock” of succession and
keeps a yard in grass. In a deflected succession, the resulting stable
community, even if it consists wholly of native species, is one that would
not have occurred in the absence of human intervention. Example: Electric
utility companies may establish shrubs in powerline right-of-ways. Tree
seedlings in dense shade beneath the shrubs don’t survive.
A common form of secondary succession takes place on abandoned farmland.
This is old field succession. Farmers cleared the original natural
communities to cultivate crops. After abandonment, land reverts via
succession. Old field succession is usually a mesosere. Let’s imagine an old
farm set in the hilly Piedmont province of the Southeast. In another U.S.
region the species composition of the communities is different but the
process is similar.
If we had enough time, say, 250 years, and there was no major
disturbance, we could watch an old farm pass through the seral stages of
bare field, pioneer, crabgrass-horseweed, aster, broomsedge, shrub, pine,
early hardwood, and finally, climax hardwood.
In each stage, the dominants or codominants are the tallest plants or
those that occupy more of a site’s area than the other plants.
Pioneers on the bare field are annual weeds: crabgrass, chickweed,
cranesbill, henbit. Associated fauna are crickets, grasshoppers, ground
beetles, cutworms, mice, and moles.
At about one year horseweed and crabgrass codominate.
At two years this stage grades into the aster stage of perennial weeds.
The field waves with asters, daisy fleabane, ragweed, Queen Anne’s lace,
milkweed, and broomsedge. Tangled greenbriar and brambles furnish food
and/or cover for insects, spiders, meadowlarks, cardinals, quail, kestrels,
toads, corn snakes, copperheads, mice, shrews, opossums, skunks, rabbits,
and foxes. Plants and animals of the early stages are known as early-successional
species.
A third-year broomsedge stage grades into a shrub stage in year four. A
furtive bobcat might be seen. Young pines and cedars emerge in the overgrown
field.
During the pine stage, years 5-50, the pines rise and form a canopy. In
the understory are small trees (e.g., sumacs, black locust), young trees
that will become emergents (e.g., sweet gum, red maple), and woody vines (e.g.,poison
ivy, trumpet creeper). The suite of animals expands. New species of insects,
lizards, and snakes appear. Nuthatches, catbirds, finches, chickadees,
vultures, owls, red-tailed and sharp-shinned hawks, flying squirrels, and
deer are inhabitants.
In years 50-90, the early hardwood stage, tulip trees, sweetgum, and red
maple grow tall enough to contend with the pines for sunlight. These
hardwoods begin to shade the sun-loving pines, most of which break down
eventually. Occupying the understory are small trees such as dogwood,
redbud, sassafras, cherry, and sourwood; young trees that will become
emergent later, the oaks and hickories; and vines. Arrowwood, huckleberry,
and mulberry are the shrubs. Animal residents may include box turtles,
scarlet- and king snakes, salamanders, and frogs.
At 90+ years climax is reached as a second wave of hardwood species, oaks
and hickories, achieve dominance. Tulip trees may be present in the canopy,
with beeches making a sub-canopy. Small trees of the previous seral stage
may be joined by hornbeam, cucumber tree, witch hazel, and blackgum. Wild
azalea and oakleaf hydrangea may add to the shrub layer. At the ground is a
layer of herbs and ferns. Invertebrates are more numerous, especially in the
leaf litter. Wood warblers, vireos, tanagers, woodpeckers, Cooper’s and
broad-winged hawks, gray and fox squirrels, bats, raccoons, gray foxes,
deer, and bobcats may be present. Plants and animals of the later stages and
climax are known as late-successional species.
Many animals, particularly mammals, use areas of various seral stages;
they do not necessarily inhabit a single stage only. White-tailed deer
shelter in areas of the shrub, pine, early hardwood, and climax stages. Deer
browse at the boundaries, or “edges,” of these habitats, and in clearings.
Wild turkey poults needing much protein frequent “bugging areas,” stands of
weeds rich with insects, while adult turkeys eat mast (nuts, acorns, and
soft fruits) in woods.
Oak-hickory is a common climax type used for the example. What climax
community is characteristic where you live? It depends on local conditions
of climate, soils, and moisture. Finding a climax community nearby to visit
may be difficult but well worth the effort.
Virgin climax communities are much-depleted ecosystems. Mature
second-growth climax communities are scarce also. Many animals (e.g.,
cerulean warblers, fishers, northern spotted owls) must have old, big
forests for habitats.
To a hiker in the backcountry of what is now Great Smoky Mountains
National Park, TN-NC, the landscape looks verdant, primeval. There are 130
tree species (more than in all of northern Europe) and 1,500 species of
flowering plants. Yet before Congress authorized the park in 1926 this was a
moonscape of rapacious logging, soil eroding from steep slopes, fires, and
mudslides.
Succession changes habitat conditions—usually in the opposite direction
of man’s activities. To the extent that people interested in animals favor
the species associated with farmland (“farm game,” early successional
species like quail, doves, rabbits, and foxes) or that require openings in
forests (“forest game” such as deer and turkeys), game managers have the
task of fighting nature to artificially maintain those conditions.
References:
Dowie, Mark. Losing Ground: American Environmentalism at the Close of the
Twentieth Century. Cambridge: MIT Press 1996. ISBN 0-262-54084-3. GE197.D68.
Godfrey, Michael A. Field Guide to the Piedmont: The Natural Habitats of
America’s Most Lived-in Region, from New York City to Montgomery, Alabama.
Chapel Hill: University of North Carolina Press 1997. ISBN 0-8078-4671-6.
QH104-5.P54G62.
Kricher, John C., & Gordon Morrison. A Field Guide to Eastern Forests,
North America. Boston: Houston Mifflin 1988. ISBN 0-395-47953-3. QH102.K75.
Livingston, John. The Fallacy of Wildlife Conservation. Toronto:
McClelland & Stewart 1981. ISBN 0-7710-5336-3. SK33.M66.
Porcher, Richard Dwight, and Douglas Alan Rayner. A Guide to the
Wildflowers of South Carolina. Columbia: University of South Carolina Press
2001. ISBN 1-57003-438-9. QK185.PB2.
---------------------------------
John Eberhart is a member of the Georgia Earth Alliance, a pro-animal nature
preservation organization. He can be contacted at: PO Box 1231, Fayetteville
GA 30214-6231, OEberhart@aol.com
How do game managers disturb natural succession to
“grow” target animals for hunters and trappers? That will be the topic of a
future article.
|
|
