Long-term study of damage to trees by brown bears Ursus arctosin Poland: Increasing trends with insignificant effects on forestmanagement

Inglés. We present a long-term quantitative analysis of forest damage caused by the brown bear (Ursus arctos)inthe biggest refuge of this species in Poland. Based on questionnaires distributed to the relevant author-ities we estimated the number of trees damaged by bears in 1991–2013, changes in the tree species com-position and large-scale factors potentially affecting the extent of damage. We also discuss theimportance of bear tree damage to forest management. Throughout the 23 years of the study we recorded6937 trees damaged by bears: a clearly increasing trend and distinct fluctuations in tree numbers andspecies composition were discernible. Conifers (91.7% – fir 70.0%, larch 11.3%, spruce 9.5%, pine 0.9%)were more frequently damaged than deciduous species (2.9%). Larch and spruce were preferentiallyaffected during the whole study period, and the preference for larch was distinct when collated withits availability in forest stands – a forage ratio of 0.50 compared to 0.35 for fir, 0.17 for spruce and0.13 for pine. In 2003, however, bears suddenly switched to fir and it is this species that now predomi-nates among the damaged trees, reaching 96.5% in 2013.Two models based on minimum AICcvalues were best explaining damage to trees. The most parsimo-nious model contained one explanatory variable: brown bear population size. The second best modelincluded both bear population size and the average fir tree-ring width. Neither fluctuations in daily tem-peratures nor the number of days with snow cover had any influence on the scale of damage. Our findingssuggest that damage caused by bears is not to be regarded as a serious problem by forest management inPoland and it is unlikely to reach a level of economic significance in the short term

Inglés. Damage to forests, Long-term trends, Tree damage, Foraging behavior, Forest economy, Carpathians

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