Impact of Climate Trends and Drought Events on the Growth of Oaks (Quercus robur L. and Quercus petraea (Matt.) Liebl.) within and beyond Their Natural Range

Diana Perkins,Vinicio Carraro,Ben Du Toit,Peter Biber,Thomas Rötzer,Enno Uhl,Hans Pretzsch

doi:10.3390/f9030108

Diana Perkins, Vinicio Carraro + Show 5 more

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https://doi.org/10.3390/f9030108

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Abstract

Due to predicted climate change, it is important to know to what extent trees and forests will be impacted by chronic and episodic drought stress. As oaks play an important role in European forestry, this study focuses on the growth response of sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Quercus robur (L.)) under contrasting climatic conditions. Analyses cover both site conditions of their natural occurrence (Southern Germany and Northeast Italy) and site conditions beyond their natural range (South Africa). The sites beyond their natural range represent possible future climate conditions. Tree-ring series from three different sites were compared and analysed using dendrochronological methods. The long-term growth development of oak trees appears to be similar across the sites, yet the growth level over time is higher in the drier and warmer climate than in the temperate zone. When compared with previous growth periods, growth models reveal that oak trees grew more than expected during the last decades. A recent setback in growth can be observed, although growth is still higher than the model predicts. By focusing on the short-term reactions of the trees, distinct drought events and periods were discovered. In each climatic region, similar growth reactions developed after drought periods. A decline in growth rate occurred in the second or third year after the drought event. Oaks in South Africa are currently exposed to a warmer climate with more frequent drought events. This climatic condition is a future prediction also for Europe. In view of this climate change, we discuss the consequences of the long- and short- term growth behaviour of oaks grown in the climate of South Africa for a tree species selection that naturally occurs in Europe.

Highlights

Knowledge of the resilience and resistance of tree species is crucial for forestry in a changing climate
To study how growth patterns of oaks (Quercus spp.) differ outside their natural distribution area compared to their origin habitat, we focus on Quercus robur L. and Quercus petraea (Matt.) Liebl
The selected trees at the four German, the four Italian, and the nine South African research sites covered a representative scope of age, height, and diameter at breast height (DBH) (Table 1)

Summary

Introduction

Knowledge of the resilience and resistance of tree species is crucial for forestry in a changing climate. In order to generate respective knowledge, the growth and vitality of trees is often studied along. Such studies mostly include growth modelling of trees growing on the edge of their natural distribution [1,2,3,4] and trees that experienced drought conditions [5]. This information can provide valuable insight into the species-specific resilience and resistance under drought stress. Any statistical relationships between climate conditions and occurrence have the shortcoming of all statistical relationships: that conclusions concerning causalities are questionable

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