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Document Type

Bryce Canyon National Park

First Page

53

Last Page

60

Abstract

The composition and distribution of plant communities across a natural landscape is determined by a complex interaction of environment, interspecies relations and disturbance. Environmental factors associated with particular locations, such as precipitation and temperature regimes, limit the species which can occur at a given site to those with a metabolism suited to the environmental conditions. These environmental factors, while variable across the landscape, are relatively constant at a fixed point in space. Consequently, environment acts as a relatively constant constraint on vegetation distribution and composition. Within the usually large set of species which can exist at a given point, interspecies competition further limits the species present at a given time. The ecological characteristics of the species are also rather fixed, and the interspecies relations lead to a fairly directional and predictable change with time, i.e. succession. Disturbance reduces or eliminates some species directly, and leads indirectly to changes in composition through changes in the competitive hierarchy. In contrast to environmental and interspecies effects, the occurrence and effects of disturbance are highly variable, and depend in a complex way on previous disturbance and the current and previous vegetation. Historically, fire played an enormous role in determining the characteristics of vegetation in western forests. Additionally, fire suppression has preserved species which would have been reduced or eliminated under a regime of repeated burning, and has led to an increase in fuel loads in many natural communities. The high fuel loads cause relatively severe fires when fires do occur, causing relatively greater disturbance than occurred in the historical past. The results of these high intensity fires are very different from low intensity fires, with increased mortality of even fire-tolerant species, and occasionally catastrophic results. To evaluate the current landscape with reference to the historic landscape information is needed in several related areas. First, more baseline information is required on the historic vegetation mosaic. Specifically, what was the distribution of plant communities on the historic landscape, and what was the typical composition of these communities? Second, how does the pattern compare to the current pattern and how is this relation affected by the vegetation potential of the environment and the interspecies relations? How can natural ecosystem processes, including fire, be reintroduced so as to return the vegetation mosaic to one more similar to the historic vegetation mosaic? How can the guidelines which emerge from this information be implemented in an operational and spatially-explicit manner? These information needs are best met through a comprehensive information system incorporating the basic ecological relations of the vegetation and environment, fuel load accumulation, and fire behavior models.

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