Ecosystems regress under stress.
Marine ecologist Kenneth Sherman and colleagues (1981), for example,
cataloged species in ecosystems under pressure from commercial fishing. The
Removal of larger, long-lived commercial fish associated with climax
ecosystems resulted in a population boom of less-valuable sand eels.
Researchers linked the smaller, more quickly breeding sand eels to
depleted catches of commercially important herring and mackerel. Here
is an example of succession being pushed backward. Abundant stocks
of herring and mackerel typify the climax marine ecosystems beloved
by fishermen. Removing these fish plunged the ecosystems to earlier
stages of development marked by greater numbers of members of faster-growing
species. Such ecosystem reversal appears to be universal. Depriving ecosystems
of sufficient energy or upsetting their interconnected integrity decimates
their degrading capacities, physiologically forcing them back into states
they had already grown out of. Psychological regression in humans also
seems prompted by reduced energy or stress. When the energy available
for the formation of complex systems is taken away, these systems revert
to a more primitive level of function.
The clear-cutting of oak and fir is the terrestrial equivalent to draining
mature fisheries stocks from the ocean. Since ecosystems are nested networks,
stressing them does not usually kill them but rather sends them back
to an earlier stage of complexity, when they are being colonized by more
fecund species, the r pioneers of the successional process. The reversion
in ecosystems is similar to that in nonliving systems such as the Taylor
vortices, whose pairs of rotating whirlpools diminish when their pressure
gradient decreases. In both living and nonliving systems the reversion
to earlier modes is triggered by reduced energy flows. Stress sends the
gradient-reducing system back to earlier modes able to make do on less
energy.
On a planetary level, humans resemble a pioneer
species. In a few generations, we have multiplied prolifically. The
rapid growth resembles the high-entropy phase of a new ecosystem. But
if we are truly the r species of a global ecosystem, we do not know
what that ecosystem is—it has not existed
on Earth before. Becoming stewards of the Earth is a noble calling. But
the more rapidly a species proliferates, the higher the probability that
viruses, bacteria, fungi, and animals will treat that species as a succulent
gradient to be devoured. This moderates the lopsided growth of one part
of the system at the expense of the rest. A peak global ecosystem would
seem to entail greater species diversity and higher global ecosystem
efficiency than we see at present. It would also seem to involve fewer
humans.
All individual organisms are bounded by structures of their own making.
A tree is enclosed by bark, mammals are encapsulated by hairy skin, and
gram-negative bacterial cells have walls enclosed in membranes. Ecosystems
also have boundaries. A mature ecosystem leaks very little nutrients
and water. Like a cell, it synthesizes its transparent outer membrane
itself.
At the Hubbard Brook Experimental Forest in New Hampshire an experiment
measuring how well stressed ecosystems maintain their materials began
in 1965. It is still going on today. Yale University professors Gene
Likens, F. Herbert Bormann, and their colleagues studied sites maintained
by the U.S. National Forest Service. Gene Likens's lifelong research
program focuses on the biogeochemistry of forest ecosystems. His long-term
studies at the Hubbard Brook Experimental Forest, which he cofounded
with Bormann, have shed light on critical links between ecosystem functions
and land-use practices. A watershed in Hubbard Brook forest was sprayed
with herbicides after woods were clear-cut in the fall and winter of
1965. For several years following this ill treatment, researchers monitored
the water and nutrient flow through this drainage basin. They compared
the results with those from similar drainage basins in the surrounding
woods that had not been cut or sprayed. The results were dramatic.
The stream runoff—the watery leak—for the deforested system
increased by 39% the first year and 28% the second year. Blasted by
pesticides back to a very early successional stage, the integrity of
the ecosystem drastically declined. It now leaked its most valuable
resource, water. Other valuable materials, phosphate and nitrate, were
also lost at a much greater rate than in the undamaged basins. Nitrate
loss increased forty-one-fold. This meant nitrogen in the herbicide-treated
area was far less available to organisms to make their proteins and
nucleic acids.
The "stressed" ecosystem (the cut and sprayed watershed)
leaked nutrients, water, and sediments. The more mature, uncut watersheds
recycled these materials. Increased cycling of material and energy
is a hallmark of a mature dissipative system.
Pesticides, radiation, and oil cause ecosystems to malfunction. Such
systems are impaired. They no longer capture as much energy or build
the intricate structures that they once did. They no longer expand along
natural successional trajectories toward maturity. After many clear-cuts
in the western United States, the successional fir forests have been
replaced by lodgepole pine. These drastic changes in giant human-sustaining
ecosystems, unlike those at Hubbard Brook, are not merely affecting experimental
areas.
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