EXAMINING GEOLOGIC AND ECOLOGIC RESPONSES TO MAJOR DISTURBANCE

Geologic and ecologic responses to severe, large-scale disturbance are commonly highly coupled, yet we tend to examine disturbance events and responses to them from single, disciplinary viewpoints. Drawing on examples from widlfire, landslide, and volcanic disturbances, I suggest two perspecitves may enhance understanding of these coupled responses. First, characterization of physical disturbances in terms of the mechanisms affecting organisms (e.g., heat, impact force, depth of erosion or burial) gives a stronger basis for interpreting and predicting biotic response than does simple definition of the process types (e.g., mudflow, fire). This may require geologists to examine ephemeral and peripheral aspects of geologic events and features in non-traditional ways. Second, the well-developed concept of biotic succession following disturbance may have useful parallels in terms of succession of geophysical processes in response to altered landscape hydrology and sediment availability. For example, disturbances that alter the soil surface, such as fire-induced hydrophobicity and tephra deposition, temporarily reduce infiltration capacity, enhancing water runoff; subsequent rill formation and other processes provide water access into the soil, reducing runoff; the infiltrating water may then trigger shallow slides on marginally-stable slopes. The pace of landscape response involves both these on-site successional phenomena and the passage of mobilized sediment and other materials through the landscape.