Transcript Slides

ESRM 501
5/7/07
Natural Disturbance
Doug Sprugel
“As a consequence of almost universal use and
misuse by man, subseres [successional
communities developing after disturbance] in
possible stage of succession constitute the most
abundant of all every communities… In regions
long-settled, subseres form practically the entire
cover of vegetation” (Weaver and Clements, Plant
Ecology, 1938, p. 78)
But
“Before the advent of civilized man, nearly the
whole area of each climax was occupied by the
[climax] dominant species” (ibid., p. 479)
.
- lodgepole pine forests in Rocky Mts.
(including Yellowstone) [catastrophic fires]
- mixed conifer forests in the Sierras (e.g.
Sequoia Nat’l Park) [surface fires]
- ponderosa pine in Arizona and eastern
Washington [surface fires]
- East Coast (esp. Florida and Harvard
Forest, Mass.) [hurricanes]
- Northeastern mountains [spruce budworm
outbreaks and fir waves]
.
.
.
.
.
Take-home message 1. Disturbance is a
normal component of most natural
ecosystems and exerts a powerful control
on vegetation characteristics. Many plants
and animals are well adapted to particular
kinds of disturbances and often can’t
survive without them.
Disturbance characteristics:
1. Disturbance type
.
Disturbance characteristics:
1. Disturbance type
1.
2. Intensity
3. Frequency
4. Size
Types of disturbance: Surface fire
--examples: ponderosa pine and Sierran mixed
conifer forests
--adaptations: thick bark, rapid early growth,
absence of low branches, "grass stage" of longleaf
pine
--effects of fire suppression—major changes in
ecosystem structure and function.
Types of disturbance: Stand-destroying or
catastrophic fire
--example: lodgepole pine forests; Western
Washington Douglas-fir forests
--adaptations: numerous small seeds with
dormancy; serotinous cones; shade-intolerant.
Seeds able to grow on exposed soil.
--effects of fire suppression--largely insignificant
Why should we care?
Understanding basic ecology can advise
management
Unexpected consequences of fire control
Management of natural areas
Endangered species management
Impacts on planning
Effects of climate change