Dynamic interactions between forest structure and fire behavior in boreal ecosystems

This paper reviews and synthesizes literature on fi re as a disturbance factor in boreal forests. Spatial and temporal variation in the biophysical environment, specifi cally, vegetative structure, terrain, and weather lead to variations in fi re behavior. Changes in slope, aspect, elevation, and soil affect site energy and water budgets and the potential plant community. These terrain features also have a major infl uence on fi re-caused disturbance through their role in determining moisture conditions and fl ammability of fuels on hourly, seasonal, and successional time-scales. On fi ne time scales (minutes to hours), changes in weather, specifi cally wind and relative humidity, signifi cantly affect a fi re’s intensity and aboveground effects. Normal seasonal changes in dryness and periodic drought infl uence fi re intensity and severity principally by affecting the depth of burn and belowground effects. On decades-long time scales changes in vegetative structure affect the mass of fuel available for burning and therefore the potential energy that can be released during a fi re. The severity of fi re varies in time and space depending not only on the biophysical environment, but also on the location on the fi re’s perimeter (head vs. fl ank vs. rear). Spatial and temporal variation in severity within a fi re can have long-lasting impacts on the structure and species composition of post-fi re communities and the potential for future disturbances. Characteristic temperature histories of ground, surface, and crown fi res are used to illustrate variations in fi re severity. A soil-heating model is used to illustrate the impact of varying depth of burn on the depth at which various fi re effects occur in the soil profi le. A conceptual model is presented for the effects of fi re severity on fi re-plant regeneration interactions. The conceptual model can be used by restoration ecologists to evaluate the differential effects of controlled or prescribed fi res and wildfi res and to plan and implement fi re treatments to conserve biodiversity.