Different management and restoration options for boreal forest – role of fire in the palette

Abstract

Fire is ecologically a very effective method to maintain and restore disturbance-based properties of boreal forests. In particular, whenever fire suppression has reduced fires during longer, i.e. decadal or centennial periods, introducing fire back to ecosystems produces immediate benefits for several taxa. In addition to the benefits that fire has on fire-associated biota, fire also diversifies forest structure and initiates succession that produce long-term forest structures that later on benefit several forest-dwelling taxa.

However, applying fire as a management or restoration tool is challenging due to several factors that complicate the outcome of a forest fire. Fire or prescribed or controlled burning is typically a very heterogeneous disturbance event that is modified by several factors. These factors are mostly associated with the fire severity. The resulting forest structures and the effects that burning has on biota appear to critically depend on this variability and heterogeneity. Furthermore, based on the historical patterns of fire in a landscape, the effects of fire on biota vary, probably depending on the available species pool that can colonize burned areas. And finally, while the effects of fire are evidently positive on many species, there are also conflicting outcomes, as some taxa may be very sensitive to fire and may thus disappear after prescribed burnings. The last issue is reflected also in conflicts that prescribed burning may cause to the provision of different ecosystem services. Based on current understanding, these conflicts are obvious at stand level but they are likely avoided by land-sparing approaches over larger blocks of forest landscapes.

In addition to the potential that fire has on restoring crucial forest properties in protected areas, the use of prescribed burnings has a significant underexploited potential in managed forests. In managed areas, fire is applied together with timber-harvesting operations. Fire and the substrates that a fire creates appear to be a significant tool to maintain species diversity after intensive harvesting. However, as in the restorative burnings in protected areas, several factors seem to modify the effects that fires have, and it is likely that burning harvested sites is mainly a complementary method to promote biodiversity. Nevertheless, long tradition of silvicultural prescribed burnings - to enhance soils and tree regeneration - provides also biodiversity benefits that have remained largely unknown so far.

In conclusion, almost complete disappearance of fires from several regions in boreal forests has been a major ecological change. Together with simultaneously introduced clear-cut harvesting practices, the disturbance regimes over large areas have drastically changed, leading to impoverishment of forest habitats and species. A novel combination of fires and forest harvests holds a major promise to sustain forest biodiversity in future landscapes.