Chapter 11. Inherent Disturbance Regimes

Abstract

Summary A science-based ecosystem management approach requires valid reference points to assess the long-term maintenance of forest systems. Historical range of variability (HRV) in vegetation patterns has served as the initial reference point and has support in the coarse-filter approach to conserving biodiversity (Hunter 1991). The HRV becomes less useful as a reference with increasing human disturbance on the landscape, public aversion to treatments to restore historical states, and continued public expectations for non-historical conditions. The inherent disturbance regime (IDR) is put forward as an alternative or to be used in combination with HRV as a suitable reference point for evaluating long-term maintenance of human-altered ecosystems. The IDR is defined by the types of disturbance; their frequency, intensity, and extent in turn defines the vegetation composition and structure supported over time. Although public expectations for vegetation conditions may differ from historical, these altered states may also be supported by IDR and have long-term maintenance potential. The use of a disturbance reference (IDR) rather than a condition reference (HRV) appears more compatible with the dynamic nature of forests. As an accurate description of historical conditions and disturbance regimes is difficult we recommend that both references be used reiteratively to better refine the other. Increased discontinuity between public expectations for forest conditions and the ability of those conditions to be supported by disturbance regimes may lead to catastrophic disturbance events and a decline in long-term site nutrient capital and biodiversity.