Population dynamics and regulation of the Middle Spotted Woodpecker in strictly protected and managed forests in Western Poland

Abstract

Analysis of ecological time series allows to assess the relative contribution of density-dependent and density-independent factors influencing the regulation of the population of a species. In this study, we investigated whether the annual fluctuation in the population of Middle Spotted Woodpeckers Dendrocoptes medius can be attributed to the direct or delayed density-dependent regulation or to the density-independent factors such as weather conditions during the preceding winter and previous breeding season and/or disturbance in the habitat associated with sanitary felling and salvage logging of trees. This study was conducted in the Czeszewo Forest Reserve, which protects the remnants of semi-natural flood-plain forest, and in the Łówkowiec Forest, which is a managed oak-dominated stand, during 19 seasons (2001–2019). Time series diagnostic revealed that the growth rate of population of Middle Spotted Woodpecker in protected semi-natural riverine forest and in managed oak forest was determined by first-order negative feedback, suggesting an important role of direct density-dependent mortality in the regulation of an equilibrium in population size. The effect of density-dependent process varied between study sites, being lower in riverine forest, where population size has increased distinctly in recent years. In both study areas, we detected strong positive effects of wind chill temperature during the preceding winter on population growth rates. We did not find evidence for the assumption that the increase in population growth rate is affected by weather conditions in the previous breeding season and by the disturbance in the habitat associated with sanitary felling and salvage logging of trees. Our results suggest that Middle Spotted Woodpeckers can benefit from global climate warming by an enhanced rate of winter survival or an increase in the accessibility of food, e.g., insects and other arthropods. The lack of time-lag significant correlations between population fluctuations suggests local habitat conditions, e.g., forest management, can modify inter-annual variability in time series of the Middle Spotted Woodpecker.