Succession patterns and the role of fire in long-term dynamics of a mixed deciduous stand in Białowieża Forest, Poland

Abstract: In temperate Europe, the ecological importance of fire is poorly understood, especially in the dynamics of forests with high share of broadleaved tree species. The aim of this thesis was to explore the role of fire in a 43-ha mixed-deciduous forest stand in Białowieża Forest, NE Poland. The changes in the tree species composition were investigated using dendrochronological data obtained from three circular 5000 m2 sample plots and one 25m-long transect. In addition, to reconstruct the local fire history, all fire-scarred trees from the whole stand were cored and cross-sections from pine and oak stumps were collected. From 288 cores and one pine stump, tree establishment back to the end of the 1500s and 19 fire events between 1720 and 1908 were reconstructed. The stand’s age structure revealed a shift from light-demanding fire-adapted species (oak and pine) to shade-tolerant fire-sensitive species (hornbeam and lime) undergoing a transitional phase with codominance of a plastic species (spruce). Up to the end of the 18th century, oak and pine regenerated sporadically under frequent fires. The change gradually began with relaxation in the fire regime in the first half of the 19th century. This permitted more seedlings to survive and initiated cohorts of both oak and pine, followed by spruce encroachment. The canopy became denser, likely leading to more humid and less flammable fuel conditions after mid-1800s. Thus, the fires propagated less, permitting recruitment of more shade-tolerant species up to date. The data suggests that fire exclusion played an important role in the cessation of oak and pine regeneration in the studied stand. To my knowledge, this study is one of the first in temperate Europe highlighting the role of fire in shaping the long-term vegetation dyamics of mixed-deciduous forest ecosystems.