Forest age distribution under mixed-severity fire regimes – a simulation-based analysis for middle boreal Fennoscandia

Abstract

Pennanen, J. 2002. Forest age distribution under mixed-severity fi re regimes -a simulationbased analysis for middle boreal Fennoscandia. Silva Fennica 36(1): 213-231.A simulation model was used to study the age structure of unmanaged forest landscapes under different fi re regimes. Stand age was defi ned as the age of the oldest tree cohort in a stand. When most fi res 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 fi res are both frequent and severe. Simulation results and analytical calculations show that if a regime of frequent fi res (about every 50 y) maintains landscapes dominated by old-growth forests, then old-growth dominance persists when the number of fi res is decreased, despite the associated increase in fi re severity. Simulation results were applied to Pinus sylvestrisdominated landscapes of middle boreal Fennoscandia, which according to empirical results were dominated by old-growth forests when fi res were frequent during the 19th century. Since the changes in the fi re 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 fi res were less frequent. The simulation model is used to produce plausible age distributions of middle boreal Fennoscandian forest landscapes under different historical fi re regimes. In summary, the frequency of large-scale disturbance alone predicts forest landscape dynamics poorly, and the roles played by fi re severity and residual stands need to be considered carefully. Maintaining and restoring oldgrowth structures is essential to regaining the natural variability of Fennoscandian forest landscapes.

Forest age distribution and traces of past fires in a natural boreal landscape dominated by Picea abies

“…The observed age class distribution is close to a situation, where the forest age is determined by the maximum biological age of the trees. A low-intensity fi re regime could be also the cause of this kind of forest age distribution (Pennanen 2002). However, no evidence for the occurrence of frequent sub-lethal fi res was found in the area.…”

Monitoring Current Status of and Trends in Boreal Forest Land Use in Russian Karelia

“…By resolution we refer not only to the spatial and temporal scales at which the scenarios are implemented, but also to the number and sophistication of the submodels they incorporate. Future work in the Vienansalo framework could implement stand-level modeling such as the type used by Pennanen (2002). However, the more site-specific and detailed the modeling exercise is, the more accurate the input data need to be, a condition that cannot always be met in landscape-level research in remote areas.…”

“…859 191.335 194.969 194.626 194.5 195.536 196.29 196.551 196.913 197.665 We suggest that there is a growing demand for this type of synthetic approach to assessing forest fragmentation at the landscape level. Through multitemporal monitoring, the modeling of past and present patterns can be explored and prognoses made for the future (Baker 1989, Pennanen 2002). The methodology is especially appealing because the satellite imagery required is relatively inexpensive, and some of the tools, e.g., the Spatially Explicit Landscape Event Simulator, are free.…”

Ecological effects of disturbance-based restoration in boreal forests

“…In practice, this implies that combinations and compromises are also necessary. Of the treatments included in this thesis, the use of prescribed fire is perhaps the closest analog to a natural disturbance, although its effects can be expected to differ markedly from wildfires that have a greater variability in their extent and severity (Zackrisson 1977;Pennanen 2002;Kuuluvainen & Aakala 2011). Therefore, if high-intensity crown fires cannot be prescribed, as they are often difficult to control, it is advisable to kill some of the trees prior to burning the forests, either by the creation of canopy gaps or by thinning the forests to varying degrees (I).…”