PEST INTERACTIONS AND CANOPY GAPS IN PONDEROSA PINE STANDS IN THE BLACK-HILLS, SOUTH-DAKOTA, USA

Gap frequency and size, cause (predisposing factors, killing agents, and tree response), and coarse woody debris composition (snags and downed logs) were assessed in three stands differing in management history. Disturbance agents were usually coupled concurrently and sequentially. A qualitative model (relational diagram) developed to display these interactions and the activity distributed among different disturbance pathways suggests that management activity (1) diminishes pest-caused structural diversity in the forest ecosystem, (2) decreases functional diversity associated with interacting diseases, insects and other disturbance agents, and (3) alters the abundance and decomposition distribution of dead wood.