Landform effects on ecosystem patterns and processes.
The effects of landforms on ecosystem development and change have several important implications for the devel- oping field of landscape ecology (For- man and Godron 1986, Naveh 1982, Risser et al. 1984). Landscape ecolo- gy as defined by Risser considers the development and dynamics of spatial heterogeneity, spatial and temporal interactions and exchanges across heterogeneous landscapes, influences of spatial heterogeneity on biotic and abiotic processes, and management of spatial heterogeneity. In this article we have identified various ways in which patterns of ecosystem struc- ture, composition, and function are controlled by landforms and geomor- phic processes. Knowledge of these geomorphic underpinnings of ecosys- tems is essential to interpreting eco- systems in the context of their landscapes. The influence of landforms on pat- terns of soil, vegetation, animals, and aquatic ecosystems across a landscape contribute to developing and main- taining a patchwork ecosystem. This influence occurs through the effects of landforms on environmental gradi- ents (class 1 and 2 effects) and regula- tion by landform of the patterns and frequency of the disturbance (class 3 and 4 effects). To date, the full t trum of landform effects has received little attention in the literature of landscape ecology. Several points emerge: In general, patterns of landscape and landforms are easier to observe than ecosystem processes, so an un- derstanding of how landforms affect processes yields some power in pre- dicting ecosystem behavior. The ef- fects of landscape position and soil factors on lake processes, for exam- ple, imply that lakes high in the landscape will be more sensitive to acid deposition than lower lakes (Eilers et al. 1983). Therefore, posi- tion within a drainage basin is important factor in designing sam- pling programs for many aspects of lake water chemistry and biology. Patterns of soils and vegetation studied in the shortgrass steppe of Colorado indicate that landform- ecosystem interactions may take multiple forms and that patterns imposed by one set of interactions may be overridden by another set. Careful field studies to explore mul- tiple working hypotheses are essen- tial to elucidating the full range of important interactions. The interactions of landform effects on ecosystem development during periods without major disturbance and on movement of disturbances across a landscape may influence strongly the persistence and geome- try of the landscape mosaic defined by patches of vegetation, soils, or other ecosystem components. To our knowledge, these important in- teractions have not been examined quantitatively. These concepts of landform effects on ecosystems provide broad temporal and spatial perspectives for designing sampling of soil, vegetation, and aquatic ecosystems and for interpret- ing community and ecosystem pro- cesses in dynamic landscape.