Another piece in conservation biology's big-picture puzzle is the
importance of natural disturbances. Caribbean forests are adapted to
periodic hurricanes and eastern temperate North American forests to
tornadoes, blowdowns, and ice storms. Many plant communities in
North America evolved with wildfire. Floods are crucial to
establishment of new trees in riparian forests. Carnivores exercise
top-down regulation of prey species numbers and behaviors.
Such disturbances help maintain the natural mosaic of landscapes and
natural vegetation types. Fragmentation of habitat, however, changes
the scale of events and thus the effect. If a wildland is too small
and isolated, a disturbance can affect or perturb all of it, thus
eliminating a habitat type for a long time.
To be viable, habitats must be large enough to absorb major
natural disturbances (types of
stochastic events). As early as 1978, ecologists S. T.
A. Pickett and J. N. Thompson argued that nature reserves needed to
be big enough for natural disturbance regimes. They termed this a
minimum dynamic area. When Yellowstone burned in 1988, there was
a great hue and cry over the imagined devastation, but researchers
have found that the fire was natural and beneficial. Because
Yellowstone National Park covers 2 million acres and is abutted by
several million acres more of national forest wilderness areas, the
extensive fires affected only a portion of the total reserve area
and were well within the bounds of historical natural disturbance.
Daniel Simberloff and his coauthors in chapter 4 of Continental
Conservation identify fire, hydrology, and predation as the
ecologically most essential natural processes to restore. All have
been severely disrupted throughout North America south of the boreal
forest.
(Adapted and condensed
from Rewilding North America
by Dave Foreman [Chapter 7]. Copyright © 2004 by the author.
Reproduced by permission of Island Press, Washington, D.C.
Books
Rewilding North
America: A Vision for Conservation in the 21st Century
by Dave Foreman (Island Press 2004).
Order from The Rewilding Project.
Continental
Conservation: Scientific Foundations of Regional Reserve Networks
edited by Michael E. Soulè and John Terborgh (Island Press
1999). Particularly Chapter 4 “Regional and Continental
Restoration.” Order
from The Rewilding Project.
Saving Nature’s
Legacy: Protecting and Restoring Biodiversity by Reed F. Noss
and Allen Y. Cooperrider (Island Press 1994). Order from Amazon.
“Examines the distinctive character of large-scale ecological
processes” and their application to conservation biology.
Status and Trends
of the Nation’s Biological Resources Vol. 1 edited by Michael J.
Mac et al. (U.S. Geological Service 1998). Order from Amazon.
Large-Scale Ecology
and Conservation Biology edited by P.J. Edwards, R.M. May, and
N.R. Webb (Blackwell, Oxford, England, 1994. Order from Amazon.
Fire, Native
Peoples, and The Natural Landscape edited by Thomas R. Vale
(Island Press 2002). Physical geographers (as opposed to
cultural geographers) study their regions of expertise in the United
States to determine the relative role of Indian use of fire to
“domesticate” the continent before Columbus. They find that
wilderness deconstructionists and others grossly overstate this role
and that natural ignition sources (lightening) better explain the
prevalence of fire. The anthology is also an excellent
overview of the incidence and ecological role of fire in many North
American ecosystems.
Articles
Available in a book
listed above:
Daniel Simberloff et
al. “Regional and Continental Restoration,” Chapter 4 in
Continental Conservation.
Stewart T. A. Pickett,
“Natural Processes,” in Status and Trends of the Nation’s
Biological Resources, 11-36.
