47 Forum für Wissen 2004: 47–54 Range of Variability of unmanaged subalpine forests Dominik Kulakowski, Peter Bebi Eidg. Institut für Schnee- und Lawinenforschung SLF, Flüelastrasse 11, CH-7260 Davos kulakowski@slf.ch, bebi@slf.ch ecosystems to form hypotheses about the natural structure and function of these forests. In the present paper, we discuss the concept of NRV, briefly review components of NRV of the sub- alpine forests of the Colorado Rockies and discuss the potential relevance of NRV of those forests to forming hy- potheses about natural forest processes in the Alps. Because important differences in ecosystems can exist even over small distances, lessons from other forests can only be considered as untested hypotheses. However, such hypothesis and related general principles can help to form a basis for the understanding of the natural functioning of an eco- system. Much research in the forests of the Rocky Mountains has aimed to describe and understand the NRV of those eco- systems. We now consider some of the findings from the Colorado Rockies that may be relevant to a desire to manage the forests of the Alps within a natural state. The purpose of this paper is not to argue whether or not it is desirable to attempt to manage forests within their natural range of conditions, but rather to provide a first attempt to hypothesize how such conditions may look. 2 Natural Range of Variability Modern management increasingly aims to maintain patterns and processes within their Range of Historical, or Natural, Variability. Because this con- cept has been mostly applied in western North America, where natural ecosystem development has only recently (e.g. 19 th century in the Colorado Rocky Mountains) been affected by modern society, it is often termed the Historical Range of Variability. However, for ecosystems that have had a long history of intense human modification, the term Natural Range of Variability may be more appropriate.The fundamental premises of natural variability are that natural conditions and processes provide the best guideline for sustainable eco- system management and that natural disturbances are a vital attribute of most ecological systems (LANDRES et al. 1999). This dynamic picture portrays how ecosystems have perpetuated and sustained themselves and thus it is the best, if not the only, true model of sustainability. Dendroecology and other lines of inquiry can describe key components of NRV if evidence of natural ecological conditions still exists and can be collec- ted. If evidence of NRV no longer exists in a particular ecosystem then, by necessity, one can consider general 1 Introduction The best, if not the only, true model of ecological sustainability is based on restoring or maintaining the Natural, or Historical,Range of Variation (NRV or HRV) of ecosystem patterns and processes (LANDRES et al. 1999). For reasons of economic viability and soci- al values, there is increasing interest in managing the subalpine forests of the Alps in a more natural state (KRÄUCHI et al. 2000; SCHÖNENBERGER 2001). Furthermore, there is an associated need to understand resistance and ela- sticity of forests of the Alps in relation to natural disturbances (BRANG 2001). Managing ecosystems within NRV requires an understanding of how eco- systems function in the absence of major anthropogenic influences. Because almost no information is available on the NRV for the subalpine forests of the Alps, it is necessary to draw on knowledge from comparable Managing ecosystems within their natural range of variation is a promising approach for promoting ecosystem sustainability. In some forests, such as those of the European Alps, human influences have been so longstanding and intense that almost no evidence exists of natural ecosystem structure and function. In such cases, out of necessity, one may draw on research from analogous ecosystems to formulate hypotheses about the natural range of variation of forest patterns and processes. The subalpine forests of the Swiss Alps and the Colorado Rocky Mountain share important similarities as well as important differences. Natural forest development and succession in both ecosystems occurs over the course of centuries, and thus includes a broad range of patterns, processes, and stages devel- opment. Natural disturbances are important in both ecosystems and contribute to heterogeneity at landscape scales. Both systems are adapted to recovery following natural disturbances. Increasing human settlement within these ecosystems results in hazards to human endeavors and infrastructures. In the subalpine forests of the Rockies, protecting human settlements from natural stand-replacing fires requires a departure from natural conditions around the settlements in order to reduce fire hazard. In the subalpine forests of the Alps, protecting human settlements and infrastructures of high value from avalanches and other disturbances also requires forests to be outside of a natural state in some areas. In other areas, however, forests that are shaped primarily by natural processes can also serve a protective function.