Future of Beech in Southeast Europe from the Perspective of Evolutionary Ecology

Abstract

The aim of this study is to provide quantitative information on the effect of climatic change on the growth and vitality of European beech: although the species is considered in its optimum highly plastic and adaptable, it becomes climate-sensitive closer to its xeric (lower) distribution limits. The future of beech in Southeast Europe requires special attention because this region harbours significant populations living at or near their xeric distribution boundary. Even though the low elevation occurrences are uniquely vulnerable to climatic shifts, observations and modelling studies pertaining to this region are particularly scarce. Out of climatic factors determining the xeric distributional limits for beech, Ellenberg’s drought index (EQ) appeared as the most influential. Growth response analyses in comparative tests have confirmed the existence of macroclimatic adaptation of beech and have proven that warming and more arid conditions lead to decline of growth and vitality, while no decline was observed if EQ changed in the opposite direction. The response to weather extremes was investigated in field plots. Recurrent summer droughts of 3 to 4 consecutive years, above mean EQ value 40-42 resulted in pest and disease attacks and mass mortality. The discussed approaches indicate consistently a high level of uncertainty regarding the future of beech at the xeric limit in Southeast Europe. According to field observations and bioclimatic data in Hungary, a large part of low-elevation beech forests presently in the zone of EQ index ≥20 might be threatened by the warming in the second half of the century, while higher-elevation occurrences may remain stable. The interpretation of the results bears some stipulations, such as the consequence of ecological and human interactions in influencing present distribution patterns, the unclear role of persistence, natural selection and plasticity and uncertainties of climate projections. Grim projections may probably be partly overwritten by the mentioned stipulations and by careful and prudent human support.