How Does Radial Growth of Water-Stressed Populations of European Beech (Fagus sylvatica L.) Trees Vary under Multiple Drought Events?

Tamalika Chakraborty,Albert Reif,Somidh Saha,Andreas Matzarakis

doi:10.3390/f12020129

Abstract

European beech (Fagus sylvatica L.) trees are becoming vulnerable to drought, with a warming climate. Existing studies disagree on how radial growth varies in European beech in response to droughts. We aimed to find the impact of multiple droughts on beech trees’ annual radial growth at their ecological drought limit created by soil water availability in the forest. Besides, we quantified the influence of competition and canopy openness on the mean basal area growth of beech trees. We carried out this study in five near-natural temperate forests in three localities of Germany and Switzerland. We quantified available soil water storage capacity (AWC) in plots laid in the transition zone from oak to beech dominated forests. The plots were classified as ‘dry’ (AWC < 60 mL) and ‘less-dry’ (AWC > 60 mL). We performed dendroecological analyses starting from 1951 in continuous and discontinuous series to study the influence of climatic drought (i.e., precipitation-potential evapotranspiration) on the radial growth of beech trees in dry and less-dry plots. We used observed values for this analysis and did not use interpolated values from interpolated historical records in this study. We selected six drought events to study the resistance, recovery, and resilience of beech trees to drought at a discontinuous level. The radial growth was significantly higher in less-dry plots than dry plots. The increase in drought had reduced tree growth. Frequent climatic drought events resulted in more significant correlations, hence, increased the dependency of tree growth on AWC. We showed that the recovery and resilience to climatic drought were higher in trees in less-dry plots than dry plots, but it was the opposite for resistance. The resistance, recovery, and resilience of the trees were heterogeneous between the events of drought. Mean growth of beech trees (basal area increment) were negatively impacted by neighborhood competition and positively influenced by canopy openness. We emphasized that beech trees growing on soil with low AWC are at higher risk of growth decline. We concluded that changes in soil water conditions even at the microsite level could influence beech trees’ growth in their drought limit under the changing climate. Along with drought, neighborhood competition and lack of light can also reduce beech trees’ growth. This study will enrich the state of knowledge about the ongoing debate on the vulnerability of beech trees to drought in Europe.

Highlights

Increasing summer temperature and decreasing precipitation have caused droughtinduced die-back and growth decline in the temperate forests of Europe in recent decades [1,2].European beech (Fagus sylvatica L.) trees are regarded as vulnerable to drought because of the species’ physiological constraints and the decline in tree growth [3,4,5]
Our goal was to determine whether resistance, recovery, and resilience of beech trees to extreme drought events differed between the trees growing in identical climatic conditions but with different soil water availability due to heterogeneous soil conditions
With the increasing drought severity in forest ecosystems, we conclude that the soil water will play a crucial role in maintaining radial growth for the individual beech tree even within the smaller sized forests (0.3 to 0.9 ha) if they are located at the distribution limit of the trees

Summary

Introduction

Increasing summer temperature and decreasing precipitation have caused droughtinduced die-back and growth decline in the temperate forests of Europe in recent decades [1,2].European beech (Fagus sylvatica L.) trees are regarded as vulnerable to drought because of the species’ physiological constraints and the decline in tree growth [3,4,5]. Increasing summer temperature and decreasing precipitation have caused droughtinduced die-back and growth decline in the temperate forests of Europe in recent decades [1,2]. The populations at the lower latitudinal limit of beech distribution are more vulnerable to drought than other populations [5]. In those regions, the chance of cavitation, and the susceptibility to droughtinduced death, increase, and trees are often outcompeted by more drought-tolerant species such as Quercus spp., Pinus spp., Sorbus torminalis (L.) Crantz and Sorbus aria Crantz [9,10]

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