O therefore most disturbances propagate only 2

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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. o 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 terrestrial ecosystems – 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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