Landscape variability and convergence in forest structure and function following large fires in Yellowstone National Park.

摘要

Many investigators have documented landscape heterogeneity following large disturbances, but few studies have examined the persistence of this variability over long temporal scales. The 1988 Yellowstone fires created a complex mosaic of lodgepole pine seedling densities across the burned landscape. The initial variability in stand structure may endure until the next large fires occur, but the fate of variability in postfire communities is currently not well understood. I examined the Yellowstone landscape to estimate how postfire heterogeneity in stand structure and function might change with successional time, and to determine the rates and mechanisms of these changes. First, I used digital orthophotography to map the spatial variation in seedling densities present following the 1988 fires. Second, I used age distributions and dendrochronological analysis of mature lodgepole pine stands to determine how initial variability in stand density may change with time since disturbance. Third, I examined the relationship between stemwood growth, leaf area, and stand density to determine how variation in stand function is related to that of structure, and to estimate how variability in growth and leaf area may change with stand development. Finally, I built a rule-based simulation model that describes changes in landscape pattern that result from long-term stand development.; Mapping the post-1988 seedling densities showed that densities vary in a fine-grained, complex mosaic across the landscape. Analyses of stand structure suggested that the variability of stand structure is reduced with increasing stand age, stands may develop through multiple mechanisms depending on their initial structure, and initial patterns of stand structure created by large disturbances may persist for over two centuries. Stem growth and leaf area were related to stand density, though not consistently with age, suggesting that variability in structure affects variability in stand functional characteristics. Changes in variation in stand structure has direct influences on changes in landscape pattern, causing the landscape to become more coarse-grained as stand initially dissimilar in density coalesce into larger patches. This research demonstrates that large disturbances may leave an imprint on the landscape that may be evident for centuries, even as the initial heterogeneity decreases substantially with successional time.