ORIGINAL PAPER Species response curves of oak species along climatic gradients in Turkey Emin Uğurlu & Jens Oldeland Received: 13 September 2010 / Revised: 21 December 2010 / Accepted: 22 December 2010 / Published online: 20 January 2011 # ISB 2011 Abstract The genus Quercus is one of the most important tree species in Turkey. However, little is known on the ecological preferences of Turkish oak species regarding climate. We analyzed species response curves using a HOF- model approach to describe the general pattern of oak distributions along climatic gradients and to identify the driving climatic factors for eight oak species in Turkey. While climate data were extracted from the free available worldclim dataset, occurrence data on oak species were assembled from the literature into a vegetation database (n =1,104). From the analyzed species response curves, only fa ew (16%) showed unimodal responses, while most were linear (31%) or exhibited a threshold response (31%). The driving factors were seasonality of temperature and seasonality of precipi- tation, indicating that Turkish oak species can be character- ized best by the preference of climatic stability. These findings have important implications for conservation and climate change research, which usually focuses on trends of the mean values of temperature or precipitation but less often on the seasonality. In this study, we further tested whether niche optima derived from raw mean values of occurrences could replace missing model optima due to non-responsiveness of HOF models of type I. However, we did not find this to be a satisfactory solution. Finally, we discuss the need for the construction of a national database based on phytosociological relevés for Turkey. Keywords Quercus . HOF model . Stability . Seasonality . Mediterrannean Introduction The genus Quercus is one of the most abundant and economically important genera of woody plants within the family Fagacaeae in the northern hemisphere. Quercus comprises approximately 500 species of trees and shrubs that occupy a diverse array of habitat and climate types (Manos et al. 1999). In Turkey, the total forest area is around 211,000 km 2 , of which one-third belongs to oak forest (Çolak and Rotherham 2006; Mayer 1986). As an economically important genus in Turkey, Quercus is used for coppice, timber, secondary products from acorns, for erosion control and for fodder (Borelli and Varela 2000). However, it is also one of the very problematic genera within the flora of Turkey. First, many Turkish species are heavily grazed, cut for fuel or otherwise represented by deformed specimens. In some areas, no fruiting specimen can be found. Furthermore, widespread hybridization and introgression have complicated the con- servation of oaks in Turkey. In order to preserve oak species, several in situ conservation projects for Turkish oak species have been started, i.e. by creating national parks, seed stands or gene conservation forests (Bozzano and Turok 2002). Much work has been done on the taxonomy of oak species in Europe and the Middle East (Camus 1934–1954; Kotschy 1858–1862; Menitsky 1984; Schwarz 1936, 1937; Zohary 1966). These studies diversified the genus Quercus Electronic supplementary material The online version of this article (doi:10.1007/s00484-010-0399-9) contains supplementary material, which is available to authorized users. E. Uğurlu Department of Biology-Botany, Celal Bayar University, Manisa, Turkey e-mail: emin.ugurlu@bayar.edu.tr J. Oldeland (*) Biodiversity, Ecology and Evolution of Plants, University of Hamburg, Hamburg, Germany e-mail: oldeland@botanik.uni-hamburg.de Int J Biometeorol (2012) 56:85–93 DOI 10.1007/s00484-010-0399-9