Silver fir (Abies alba Mill.) is able to thrive and prosper under meso-Mediterranean conditions

Diego Walder,Patrik Krebs,Harald Bugmann,Maria Chiara Manetti,Martina Pollastrini,Solaria Anzillotti,Marco Conedera

doi:10.1016/j.foreco.2021.119537

Abstract

The potential ecological envelope of silver fir (Abies alba Mill.) based on its present distribution suggests a high suitability for moist rather than warm and dry environments. This contrasts with paleoecological evidence reporting its former presence at low elevations under meso-Mediterranean conditions. In this study, we evaluated the growth performance of silver fir at low elevation (20–60 m a.s.l.) under meso-Mediterranean climatic conditions in Tuscany (central Italy). We conducted a dendroecological analysis on Abies alba trees along a geomorphological gradient (from depression to upper slope conditions). Climate-growth relationships were assessed by means of correlations, response functions, pointer years, and superposed epoch analysis.Silver fir was found to grow and regenerate well in these stands mixed with evergreen (e.g., Quercus ilex L.) and thermophilous deciduous Mediterranean tree species (e.g., Q. cerris L.). Summer drought was the most growth-influencing factor, with immediate (i.e., current season) negative impacts on tree-ring widths (TRW). No significant impacts were observed in the four years following extreme summer droughts, but the TRW series (which started between the 1930s and 1950s) showed a growth decline since the mid-1990s that is likely drought-related.Our results show that, provided there is a sufficiently large soil water holding capacity, silver fir provenances exist which are able to withstand Mediterranean summer droughts, can naturally and regularly regenerate in these systems, and may even dominate over typical meso-Mediterranean species. As long as annual precipitation is not too low (i.e., >850 mm) and summer drought conditions not too extreme (i.e., less than three months), silver fir has thus the potential to thrive under warm Mediterranean conditions.

Highlights

European climate is getting warmer and drier (IPCC 2013) and the frequency and intensity of extreme climatic events and related distur bance regimes are changing (Bowman et al 2014; Seidl et al 2014; Seidl et al 2017)
Our dendroecological investigation on meso-Mediterranean silver fir stands in Varramista confirms the potential of the species to thrive at the warm edge of its distribution, reaching similar growth performance as in Central Europe, in spite of substantially higher temperatures and much lower summer precipitation sums
The silver fir stands in Varramista follow the general long-term growth trends of most European silver fir populations, including a continuous reduction of tree-ring width over the last ca. 25 years as a consequence of increasing water stress

Summary

Introduction

European climate is getting warmer and drier (IPCC 2013) and the frequency and intensity of extreme climatic events and related distur bance regimes are changing (Bowman et al 2014; Seidl et al 2014; Seidl et al 2017). The current distribution of silver fir ranges from the Pyrenees to the Carpathians and from southern Italy to Poland, mainly following mountain ranges (Mauri et al 2016; Fig. 1) In such ecosystems, it represents an important keystone species significantly contributing to biodiversity conservation, stand resistance to disturbances such as wind and insects in mixtures with Norway spruce (Ott et al 1997; Rüegg 2015), as well as to forest ecosystem services, such as timber production and protection from gravitative natural hazards (Tinner et al 2013; Wolf 2003)

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