Tree rings indicate different drought resistance of a native (Abies alba Mill.) and a nonnative (Picea abies (L.) Karst.) species co-occurring at a dry site in Southern Italy Giovanna Battipaglia a,b,c, *, Matthias Saurer b , Paolo Cherubini a , Rolf T.W. Siegwolf b , M. Francesca Cotrufo c a WSL Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland b PSI Paul Scherrer Institute, CH-5232 Villigen, Switzerland c Department of Environmental Sciences, Second University of Naples, Via Vivaldi 43, I-81100 Caserta, Italy 1. Introduction Mediterranean forests are particularly sensitive to climate changes (Scarascia-Mugnozza et al., 2000). Hence, forest manage- ment can play a key role in mediating the adaptation of vegetation and preventing ecosystem degradation in the Mediterranean region and has priority on the agenda of European forest policy. Natural regeneration is generally preferred in managing European forests, but in a changing environment it is important to identify the acclimatization and adaptation capability of each tree species to improve a forest ecosystem’s resilience and productivity without reducing its complexity and the provision of goods and services. Climate change scenarios predict a likely increase in drought stress (with increased temperature and decreased precipitation) throughout Europe, with the Mediterranean region being particularly affected (IPCC, 2007). Already, the climatic trends in the Mediterranean basin during the last 50 years have been characterized by a rise in mean temperature (2–4 8C), and an increase in both the frequency and intensity of severe droughts (IPCC, 2001, 2007). In this context it is essential to study the abilities of plants at the species and individual levels to respond to climate change by modifying their wood anatomical and physiological response patterns (e.g., Baas, 1976; Gartner, 1995). Tree-ring analysis offers a unique opportunity for under- standing the response of trees to drought stress over decades, and over centuries and millennia. Trees in temperate and boreal forests (but not in the tropics) form a new wood growth layer every year (annual ring). The physical and chemical characteristics of the wood cells formed in each particular year reflect the environ- mental conditions in which the tree grew during that year, and can Forest Ecology and Management 257 (2009) 820–828 ARTICLE INFO Article history: Received 11 July 2008 Received in revised form 13 October 2008 Accepted 14 October 2008 Keywords: Abies alba Picea abies Silver fir Norway spruce Mediterranean Drought Tree rings d 13 C d 18 O ABSTRACT Climate changes induced by the anthropogenic alteration of the atmospheric radiative balance are expected to change the productivity and composition of forest ecosystems. In Europe, the Mediterranean is considered one of the most vulnerable regions according to climatic forecasts and simulations. However, although modifications in the inter-specific competition are envisaged, we still lack a clear understanding of the ability of the Mediterranean vegetation to adapt to climate changes. We investigated how two co-occurring tree species commonly used in afforestation programmes, the native Abies alba Mill. and the nonnative Picea abies L. Karst., adapt to climate change by assessing their growth performance and physiological responses in relation to past climate variability. Growth was addressed by analysing tree-ring width and carbon and oxygen stable isotopes. Statistical relationships between isotopic value and monthly climate data suggest that the two species underwent ecophysiological adaptation to Mediterranean climatic constraints. These adaptations are also expressed in the ring-width data. Based on the carbon isotope ratio reflecting the stomatal response to drought, we found that the precipitation in the first period of the growing season, i.e. early spring, is a major factor influencing the annual growth of A. alba, which although native, proved to be sensitive to drought. P. abies, on the other hand, showed a higher tolerance to summer drought stress. These findings should help define criteria for sustainability and effective forest conservation in the Mediterranean region. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Current address: Swiss Federal Institute for Forest, Snow and Landscape Research-WSL, Zu ¨ rcherstrasse 111, CH-8903 Birmensdorf, Switzer- land. Tel.: +41 44 739 2392; fax: +41 44 739 2215. E-mail address: giovanna.battipaglia@wsl.ch (G. Battipaglia). Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco 0378-1127/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2008.10.015