Maintaining and restoring biodiversity in European boreal forests by developing natural disturbance regimes

A conceptual model is presented as a guide to the maintenance and restoration of ecologically sustainable boreal forest. The model is based on the hypothesis that self‐sustained forest ecosystems can be (re‐)created, and their biodiversity developed, if forest management can simulate the composition and structure of boreal forest landscapes by introducing and maintaining disturbances leading to naturally dynamic spatial and temporal patterns of forest regeneration. The major explanatory variable in the model is the effect of wildfire on sites with different fuel characteristics and climates found in the European boreal forest. Four levels of fire intensity are distinguished, based on mean fire frequencies. These range from extremely low in some wet tall‐herb sites or sites at high altitudes or latitudes with a humid climate, where fire is absent or rare, to dry lichen‐rich sites where fire occurs often. The model is called ASIO, after the words Absent, Seldom, Infrequent and Often, indicating the four levels. Three main disturbance regimes are distinguished in the European boreal forest, based on the complex interactions between probabilistic (e.g. mean fire intervals at different site types) and random events (e.g. where and when a fire occurs): (1) gap‐phase Picea abies dynamics; (2) succession from young to old‐growth mixed deciduous/coniferous forest; and (3) multi‐cohort Pinus sylvestris dynamics. The model stems mainly from studies in Fennoscandia, but some studies from outside this region are reviewed to provide support for a more general application of the model. The model has been implemented in planning systems on the landscape level of several large Swedish forest enterprises, and is also used as an educational tool to help private land owners with the location and realization of forest management regimes. Finally, the model can be used to develop an administrative system for the monitoring of biodiversity in boreal forest.