Natural disturbance regimes in northeastern North America—evaluating silvicultural systems using natural scales and frequencies

Many scientists and foresters have begun to embrace an ecological, natural disturbance paradigm for management, but lack specific guidance on how to design systems in ways that are in harmony with natural patterns. To provide such guidance, we conducted a comprehensive literature survey of northeastern disturbances, emphasizing papers that studied late-successional, undisturbed, or presettlement forests. Evidence demonstrates convincingly that such forests were dominated by relatively frequent, partial disturbances that produced a finely patterned, diverse mosaic dominated by late-successional species and structures. In contrast, large-scale, catastrophic stand-replacing disturbances were rare, returning at intervals of at least one order of magnitude longer than gap-producing events. Graphing the contiguous areas disturbed against their corresponding return intervals shows that these important disturbance parameters are positively related; area disturbed increases exponentially as the return interval lengthens. This graph provides a convenient metric, termed the natural disturbance comparability index, against which to evaluate both single and multi-cohort silvicultural systems based on their rotations or cutting-cycles and stand or gap sizes. We review implications of these findings for silvicultural practice in the region, and offer recommendations for emulating natural disturbance regimes.