The effects of climate warming on the growth of European beech forests depend critically on thinning strategy and site productivity

Recent studies have revealed that European beech (Fagus sylvatica L) has significantly increased its growth in Central Europe during the last century but recently started to decline at the edge of its southern distribution. Climate scenarios predict an increased frequency of severe drought events in the future, which is supposed to cause a decline of beech forests even towards the northern edge. Whether the management has the potential to mitigate the negative effects of climate warming has not been fully addressed yet. In order to fill the knowledge gap, we compiled data from 29 long-term research plots (LTRP) at 8 sites across the western Carpathian Mountains (Eastern Europe). The LTRP were established in 1958-84 and measured every 4-5 years till 2015. Development of forest stand attributes including top height (htcp), mean quadratic diameter (dq), mean annual tree volume increment (iv), periodic annual volume increment (PAIV), mean annual basal area increment (BAI), and total yield production (TY) was compared with the simulations by the Slovakian yield models developed in the 1980s based on data from the period before recent climate change. Results were additionally confronted with the growth of beech forests in a larger Central European region. Results showed an increase of TY since the 1960s compared to the simulated TY, starting from the same value, ranging from 5% to 40% and mainly depending on site quality and average annual temperature. The largest increase was found on less productive sites, which was in line with the previous findings in recent literature. Interestingly, beech TY in the Western Carpathians was found to be lower by 11% on average compared to beech forests in Central Europe (Germany). Moreover, while an increase in the BAI continues in unmanaged forests, it has recently slowed down in forests managed by "free crown thinning" and it even started to decrease in less productive forests where heavy thinning from below was applied. Finally, our results showed that the responses of beech BAI to climate variation significantly depended on tree class. (C) 2016 Elsevier B.V. All rights reserved.