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

The aim of this study is to provide quantitative information on the effect of climaticchange on the growth and vitality of European beech: although the species is considered in itsoptimum 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 thisregion harbours significant populations living at or near their xeric distribution boundary. Even thoughthe low elevation occurrences are uniquely vulnerable to climatic shifts, observations and modellingstudies pertaining to this region are particularly scarce.Out of climatic factors determining the xeric distributional limits for beech, Ellenberg’s droughtindex (EQ) appeared as the most influential. Growth response analyses in comparative tests haveconfirmed the existence of macroclimatic adaptation of beech and have proven that warming and morearid conditions lead to decline of growth and vitality, while no decline was observed if EQ changed inthe opposite direction. The response to weather extremes was investigated in field plots. Recurrentsummer droughts of 3 to 4 consecutive years, above mean EQ value 40-42 resulted in pest and diseaseattacks and mass mortality.The discussed approaches indicate consistently a high level of uncertainty regarding the future ofbeech at the xeric limit in Southeast Europe. According to field observations and bioclimatic data inHungary, a large part of low-elevation beech forests presently in the zone of EQ index 20 might bethreatened by the warming in the second half of the century, while higher-elevation occurrences mayremain stable.The interpretation of the results bears some stipulations, such as the consequence of ecologicaland human interactions in influencing present distribution patterns, the unclear role of persistence,natural selection and plasticity and uncertainties of climate projections. Grim projections mayprobably be partly overwritten by the mentioned stipulations and by careful and prudent humansupport.