Modeling for ecosystem management in Minnesota pine forests

Abstract

Ecosystem management implies a concern over time periods of tens to hundreds of years for sites on a scale of tens to hundreds of hectares. Decision makers need to be able to model the likely consequences of alternative management strategies at these temporal and spatial scales. They therefore require models that can be constructed quickly and cheaply, that capture the key components of the ecosystem, that respond plausibly to management actions, and are easy to explain, modify and understand. This paper presents the frame-based modeling paradigm as a response to these needs. Frame-based modeling is used to examine the effects of soil, weather, fire and deer population density on management of the white pine ecosystem in northern Minnesota. The management objective is to maintain white pine forest. The paper describes how current understanding of seedling establishment, tree growth, competition, herbivory and the effects of fire and high winds, can be captured at a consistent level of resolution in a model that can be presented, completely, in a few pages of text. The paper goes on to describe how the model was tested at three sites in northern Minnesota, and was then used to explore alternative management strategies. Our results confirm that it is comparatively easy to maintain a forest in early successional stages by burning or clear-cutting, and in late stages by suppression of fires and control of cutting. Establishment and maintenance of mid-successional stages, such as red and white pine, is much more difficult and requires a finely-tuned balance between natural disturbance and management action. For example, the pine forest was only maintained on average for 117 years out of 1000 years (average among 1000 simulated stands) on poor soil with high fire frequency and high deer density. When the deer population was low, when all wild fires were suppressed, and when prescribed ground fires were used to promote pine establishment, years in pine was 804 out of 1000 years. The model provides guidance for management decisions to maintain the desired conditions. The paper draws some conclusions from this particular modeling exercise that are likely to be generally applicable. For example, the modeling exercise illustrates limits to what management can hope to achieve, the importance of maintaining strategies over long time periods, and the difficulties of predicting and measuring success when the time horizon is hundreds of years.