389-396 Bengtsson

The Convention on Biological Diversity commits the 177 signatory countries to conserve and sustainably use biological diversity. The long-term conservation of biodiversity requires an understanding of the processes that allow species to persist in natural as well as human-dominated ecosystems. During most of the 20th century, nature reserves and national parks have been a cornerstone in the preservation of species and natural areas. However, as more and more of the earth is modified by humans (1), the mismatches in scale between present nature reserves and the natural dynamics of ecosystems (2, 3) become more pronounced. This makes it even more difficult to achieve the goal of preserving biodiversity using reserves and national parks as the main tools. Although reserves have been crucial for preserving species and habitats in the short term, with few exceptions they have not incorporated the long-term and large-scale dynamics of ecosystems as parts of dynamic landscapes (2–5). In this article, we argue that when the natural dynamics of communities and ecosystems are taken into account, a reconsideration is required of how reserves are designed and managed as parts of dynamic landscapes increasingly dominated by humans. Reserves and national parks are geographically defined areas protected by the law, and in which human activities are restricted or prohibited (6). They are usually created with the intention to protect and preserve species and habitats, and are selected to maintain existing diversity and recreation values. Most reserves have been treated as static entities that should remain essentially the same and in the same place for centuries (7). Often, reserves are created to balance intensive land use in surrounding areas, and generally reserves have been placed on marginal lands (8, 9). With this approach there is a high risk of ending up with small areas of reserves as islands in an intensively managed landscape. Also, the spatial and temporal scales of organism and ecosystem dynamics in intensively managed landscapes will be determined by human objectives, often disconnected from the scales of natural processes (10). Since less than 3% of the earth’s surface area (6.4% of the land area) (6, 9) is protected, the traditional approach to nature reserves is unlikely to be sufficient for long-term biodiversity conservation. Neither will such a small protected area sustain the life-support systems and ecosystem services that humans depend upon. An alternative to the approach of static reserves is to recognize that humans are a part of and not apart from nature, which implies that conservation of biodiversity and preservation of ecosystem services is of concern for all land use (11, 12). Ecosystem management has been advanced as a tool to preserve biodiversity in reserves as well as managed landscapes (13–15). Ecosystems are subject to natural and human-induced disturbances at various spatial and temporal scales (5, 16). Recent work has shown that humans tend to manage frequent and sometimes intermediately frequent disturbances, without perceiving the slow and rare ones (17). This is also the case in the present design of most nature reserves and parks. In the long term, it will be difficult to exclude large disturbances. Hence, an exclusive focus on static reserves as the main tool for biodiversity conservation will lead to failure of the very idea of nature reserves. To be useful, reserves should not be isolated and static, but be regarded as parts of dynamic landscapes. The long-term goal should be to create resilient landscapes of high biodiversity that make reorganization after disturbances possible in the future. The importance of recognizing natural disturbance regimes in reserve design was emphasized already by Pickett and Thompson (3). They argued that reserves should be designed based on ‘minimum dynamic area’, defined as “the smallest area with a natural disturbance regime which maintains internal recolonization sources”. However, for several reasons this criterion is difficult to apply in real situations. Firstly, in many areas of the world, such as Europe and the US Mid-West, the remaining patches of natural ecosystems are so small, scattered and surrounded by intensively managed land that minimum dynamic area within one reserve or reserve network is impossible to achieve. Secondly, recent work on natural disturbance regimes shows that large-scale rare events in ecosystems have been given too little attention (16). Hence, minimum dynamic areas depend on the time scale of interest. Thirdly, the projected global climatic changes make any reliance on internal recolonization questionable. For the long-term sustainability of ecosystems and the services they generate, the preservation of biodiversity as insurance is often viewed as essential (11, 18). This means that a sustainable ecosystem—a system that remains functional—contains functional groups that each have a large number of substitutable insurance species that may seem to be unimportant for the present structure and function of the system (18–20). We term this network of species, their dynamic interactions between each other and the environment, and the combination of structures that make reorganization after disturbance possible; the “ecological memory” of the system (21, 22). One component of the ecological memory is the “biological legacies” discussed by, e.g. Turner et al. (23) and Franklin and MacMahon (24). The ecological memory is a key component of ecological resilience, i.e. the capacity of the system to absorb disturbances, reorganize, and maintain adaptive capacity (25). Different areas of the world have different history and hence different amounts of ecological memory available. For example, Europe has a much longer history of intense human exploitation of its ecosystems than comparable areas in North America. In most European forests the amount of biological legacies is Reserves, Resilience and Dynamic Landscapes Janne Bengtsson, Per Angelstam, Thomas Elmqvist, Urban Emanuelsson, Carl Folke, Margareta Ihse, Fredrik Moberg and Magnus Nyström