%0 Research article
%T Forest age distribution under mixed-severity fire regimes – a simulation-based analysis for middle boreal Fennoscandia
%A Pennanen, Juho
%D 2002
%J Silva Fennica
%V 36
%N 1
%R doi:10.14214/sf.559
%U https://silvafennica.fi/article/559
%X A simulation model was used to study the age structure of unmanaged  forest landscapes under different fire regimes. Stand age was defined as  the age of the oldest tree cohort in a stand. When most fires are not  stand-replacing, the theoretical equilibrium stand age distribution is  either bell-shaped or bimodal and dominated by old age-classes.  Old-growth forests (oldest cohort > 150 y) dominate the landscape  unless fires are both frequent and severe. Simulation results and  analytical calculations show that if a regime of frequent fires (about  every 50 y) maintains landscapes dominated by old-growth forests, then  old-growth dominance persists when the number of fires is decreased,  despite the associated increase in fire severity. Simulation results  were applied to Pinus sylvestris-dominated landscapes of middle boreal  Fennoscandia, which according to empirical results were dominated by  old-growth forests when fires were frequent during the 19th century.  Since the changes in the fire regime can be plausibly explained by  changes in the number of human-caused ignitions, old-growth forests have  evidently also dominated the landscapes earlier when fires were less  frequent. The simulation model is used to produce plausible age  distributions of middle boreal Fennoscandian forest landscapes under  different historical fire regimes. In summary, the frequency of  large-scale disturbance alone predicts forest landscape dynamics poorly,  and the roles played by fire severity and residual stands need to be  considered carefully. Maintaining and restoring old-growth structures is  essential to regaining the natural variability of Fennoscandian forest  landscapes.