|Natural & Human Disturbance
The Role of Natural Disturbance in the Coastal
Rainforest While humans battle over the cutting of the
forests, nature provides periodic "disturbances," which invigorate the forests
by partially destroying them.
Frequent, low-intensity fires keep fuel
from building up on ground and thereby reduce the likelihood of major conflagrations,
which are far more ravaging than 'cool', low-intensity fires. Species like ponderosa pine,
Douglas-fir, and western larch, when mature, have thick bark that insulates them from
low-intensity fires; and many shrubs like ceanothus, mountain-ash, and red-osier dogwood,
as well as herbs and grasses, resprout well after such fires. © 1996. McNulty, T. Washington. In R. Kirk (Ed.), The Enduring Forests.
Seattle: The Mountaineers, p. 102.
A dominant feature of the coastal temperate rain forest is the natural disturbance
regime. The natural fire cycle in coastal temperate rain forest is about 250 years or
longer for British Columbia (Bunnell 1995) and about 230 years or
longer in Washington and Oregon (Fahnestock, G. R., & Agee, J.
K. (1983). Biomass consumption and smoke production by prehistoric and modern forest fires
in western Washington. Journal of Forestry, 81, 653-657.)
Throughout the Siskiyous, and all of the Klamath region - as elsewhere - wildfire has
been a major shaper of the forest...Most wildfires are ignited by lightning...Native
people set fires to encourage many of the plants they relied on for food and medicines,
and those that nourished deer and other game animals...No one knows how frequently they
(indigenous people) set the fires or how big they were, but Dennis Martinez of the Takelma
Intertribal Project based in the town of Talent, near Medford, (Oregon) argues that
'people have been key players in ecosystem dynamics for a long time in the Pacific
Northwest - no less so than a key pollinator or carnivore or any other indicator species'.
© 1996. Durbin, K. Oregon. In R. Kirk (Ed.), The Enduring
Forests. Seattle: The Mountaineers, p. 46.
The most important agent for natural disturbance in these rainforests is
wind. Fire plays a much less important role, partially because the forest floor is too wet
much of the year to support an intense forest fire like the ones seen in drier forests
like Yellowstone National Park.
A "blowdown" is created
when intense winds knock down shallow-rooted trees. Blowdowns increase forest ecosystem
diversity by creating holes in the dense canopy. Sun-loving plants can grow where sunlight
reaches the forest floor through these holes. Blowdowns also provide spaces for animals to
browse. Right: This bracken fern
is an example of a plant that grows in sunlit areas created by blowdowns and clear-cuts. Photo: Ed Shay
Wind is the major agent of natural disturbance that renews and modifies temperate rain
forests. Indeed, in British Columbia, the classification of temperate rain forest
recognizes two phases on disturbance by wind. The two dominant tree species of the
hemlock-amabilis fir phase appear to benefit from a disturbance regime in which patches of
forest ranging from small clumps to stands of several hundred hectares are periodically
blown down by wind. (Bunnell, & Chan-McLeod, 1997, p.
110). "Granted with permission from The Rain Forests of
Home, P.K. Schoonmaker, B. von Hagen, and E.C. Wolf, © Ecotrust, 1997. Published by
Island Press, Washington DC and Covelo, CA. For more information, contact Island Press
directly at 1-800-828-1302, email@example.com (E-mail), or www.islandpress.org
The hemlock and amabilis fir are likely to get blown down again because
they have shallow roots and broad tops that catch the winds.
A pattern of regrowth after a blowdown is called the redceder-hemlock
phase. In this case, the trees are less likely to be blown down
because the redceder's shape is less likely to catch the winds. Drawing: British Columbia Provincial Parks,
"Principal Trees of Provincial Parks"
The redcedar-hemlock phase is dominated by redcedar with a subcanopy
of western hemlock. Stands are more open than those in the hemlock-amabilis fir phase,
crowns are less dense, and many cedars are spike-topped. The consequent lower resistance
of the canopy to wind, plus redcedar's tenacious roots, make redcedar-hemlock stands more
windfirm than hemlock - amabilis fir stands. Although wind is still a major agent of
disturbance, (among the redcedar-hemlock group) the trees blown down tend to be isolated
individuals. (Bunnell, &
Chan-McLeod, 1997, p. 111). "Granted with permission from
The Rain Forests of Home, P.K. Schoonmaker, B. von Hagen, and E.C. Wolf, © Ecotrust,
1997. Published by Island Press, Washington DC and Covelo, CA. For more information,
contact Island Press directly at 1-800-828-1302, firstname.lastname@example.org (E-mail), or
Natural and Human Forest Disturbances
Ecologists used to think that if human effects were eliminated, the land would return to
its natural state. Now we find that there is no simple definition of what is natural.
Indeed, disturbance and patchiness constitute the norm, and people are part of the
ecosystem. © 1996. Sawyer, J. O., Jr. Northern California. In R.
Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 28.
The major natural disturbances to forests in southeastern Alaska are
blowdowns...Small-scale blowdowns perpetuate the uneven aged structure of old growth
forests. © 1996. Carstensen, R. Southeast Alaska. In R. Kirk (Ed.),
The Enduring Forests. Seattle: The Mountaineers, p. 151.
Human Disturbance and the Forest Ecosystem
Ecological stability has a human dimension because we are part of the
natural world, *Martinez comments. Western culture is caught
between environmental abuse and static preservation. Neither posture is sustainable or
sustaining. © 1996. Durbin, K. Oregon. In R.
Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 48.
*Dennis Martinez works with the
Takelma Intertribal Project based in the town of Talent, near Medford, Oregon.
Studies have also found that a great amount of woody debris occurs naturally in healthy
streams...For instance, in 1870 logjams forced the Lower Willamette into five separate
channels between Eugene and Corvalis. According to reports, in one ten-year period men
pulled more than 5,500 logs measuring five to nine feet in diameter from a fifty-mile
stretch of the river. (emphasis added.) ©
1996. Durbin, K. Oregon. In R. Kirk (Ed.), The Enduring Forests. Seattle: The
Mountaineers, p. 50.
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