Supplementary data are available at Bioinformatics online.

I. 2005. Modelling epiphyte metapopulation dynamics in a dynamic forest landscape. Á/ Oikos 109: 209 Á/222.We combine simulations with spatial statistics to estimate the parameters of a metapopulation model for the epiphytic lichen Lobaria pulmonaria specializing on aspen (Populus tremula ) and goat willow (Salix caprea ) in Fennoscandian boreal oldgrowth forests. We estimated the parameters of a forest landscape model (FIN-LANDIS) by repeatedly running simulations and selecting the set of parameters for tree ecology and fire regime that reproduced empirical host tree density and spatial patterns. Second, we tested which variables were important in epiphyte colonization and estimated the dispersal kernel. Third, we run a metapopulation model for the lichen across the estimated landscape scenarios and selected values for the remaining parameters that reproduced the empirical patterns of epiphyte occurrence. There was little variation in predicted dynamics, occupancy and spatial patterns between replicate metapopulation simulations. However, more data would be required for accurately estimating the parameters of FIN-LANDIS, primarily because of the inherent stochasticity in large scale forest fires. Following the beginning of fire suppression in the study area 150 years ago, the model predicts that lichen occupancy first increases but subsequently declines. The lower occupancy in the past than at present is explained by high rate of tree destruction by fires, which increases local extinction rate in patchtracking metapopulations. In the absence of fires, the occupancy increases because of lower extinction rate, but without forest fires or alternative means of host tree regeneration, the lichen is predicted to go ultimately extinct because of severely reduced density of aspen and goat willow.

No 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.

We examined fire history and forest age distribution in an unmanaged, Picea-dominated landscape in the Paanajärvi wilderness, located in northeastern Fennoscandia and northwest Russia. Maximum tree age was determined in 61 systematically located study plots in an area of about 6600 ha. Fire scars were examined in living and dead trees in the study plots and elsewhere in the study area. Charcoal and pollen analyses of peat were performed on samples from two locations. Fires had been rare in the landscape. Nearly half of the dendrochronologically dated fires occurred in a distinct and short period, from 1859 to 1889, in the northeastern part of the area. This nonrandom occurrence of fires, together with the observed signs of past human influence, suggests an anthropogenic origin for the majority of the fires. The fact that 95% of the study area consisted of forests older than 120 years reflects the end of the occurrence of fires in the 1880s. Pollen analysis from the southwestern part of the study area showed that the site had been dominated by Picea at least during the last millennium. Charcoal analysis from the same site indicated that likely more than 1000 years had elapsed since the last fire. In general, the results suggest that the abundance of old forests, with the oldest trees being approximately 300 years of age, belongs to the natural state of a Picea-dominated landscape.Résumé : Nous avons étudié l'historique des feux et la distribution de l'âge des forêts dans un paysage non aménagé dominé par Picea dans la région sauvage de Paanajärvi située dans le nord-est de la Scandinavie et le nord-ouest de la Russie. L'âge maximum des arbres a été déterminé dans 61 placettes-échantillons systématiquement réparties dans une zone d'environ 6600 ha. Les cicatrices de feu ont été examinées sur les arbres vivants et les arbres morts dans les placetteséchantillons mais aussi ailleurs dans la zone d'étude. Des analyses du charbon de bois et du pollen présents dans la tourbe ont été réalisées sur des échantillons provenant de deux endroits. Les feux ont été rares dans le paysage. Près de la moitié des feux qui ont été datés au moyen de la dendrochronologie sont survenus dans une période de temps pré-cise et assez courte, soit de 1859 à 1889, dans la partie nord-est de la zone. Le fait que ces feux ne soient pas survenus au hasard, ainsi que la présence d'indices de l'influence humaine passée, indiquent que la majorité des feux seraient d'origine humaine. Le fait que 95 % de la zone d'étude soit couverte de forêts âgées de plus de 120 ans correspond à la fin de la période de récurrence des feux dans les années 1880. L'analyse du pollen provenant de la partie sud-ouest de la zone d'étude montre que le site a été dominé par Picea pendant le dernier millénaire. L'analyse du charbon de bois provenant du même endroit montre qu'il s'est probablement écoulé 1000 ans depuis le dernier feu. En général, les résultats indiquent que l'abondance de vieilles forêts, où les plus vieux arbres ont environ 300 ans, correspond à l'état natu...