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Unformatted text preview: f a harsh, prebiotic habitat, most disturbances are
not severe enough to reduce the environment to bare rock.
Therefore most disturbances propagate only 2 succession.
• Climax communities are dominated by a few long-lived ultracompetitors which may limit species diversity.
• Therefore community diversity is greatest before the climax
community is reached — while competitive interactions have
not yet eliminated many of the species.
– Disturbances, by preventing the climax community, may be
important for maintaining high species diversity in tropical
reefs and forests. Secondary succession following FIRE FIRE
• The large-scale fire in Yellowstone National Park in 1988 • Fire is a significant disturbance in most
– It is often a necessity in some communities
Figure 53.21 (a) Before a controlled burn. A prairie that
has not burned for several years has a high
proportion of detritus (dead grass). Heyer (b) During the burn.
(c) After the burn. Approximately one month
The detritus serves as fuel for fires.
after the controlled burn, virtually all of the
biomass in this prairie is living. (a) Soon after fire. As this photo taken soon after the fire
shows, the burn left a patchy landscape. Note the
unburned trees in the distance. (b) One year after fire. This photo of the same general area
taken the following year indicates how rapidly the community
began to recover. A variety of herbaceous plants, different
from those in the former forest, cover the ground. Figure 53.22 16...
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