Global change exacerbating Mediterranean stresses

Mediterranean forests have always had to cope with challenging environmental conditions that change across different temporal and spatial scales. However, the rapidity of current environmental change, driven by greater-than-ever human influences on natural processes, is unprecedented and has triggered renewed research endeavour into the impacts on Mediterranean ecosystems (Valladares 2008). The climate of Mediterranean areas is expected to become drier and warmer, with decreasing water availability for plants and increasing evapotranspiration (IPCC 2007). This will result in more acute physiological stress, increased importance of species-specific tolerances, plasticity and thresholds, phenological change and recruitment effects (Montserrat-Martín et al. 2009; Morin et al. 2010; Peñuelas et al. 2004). Several studies have demonstrated how the conditions currently experienced by seedlings and saplings are quite different to those when current adults recruited (Lloret & Siscart 1995; Montoya 1995). The anticipated impacts of such changes have led to a renewed interest in classic ecophysiological research into drought stress and tolerance (Wikelskia & Cooke 2006), as well as population-level studies on phenotypic plasticity and the evolution of tolerance in certain key tree species, such as Holm (Quercus ilex) and cork oaks (Q. suber) (Gimeno et al. 2009; Ramírez-Valiente et al. 2010).

Niche modelling techniques are used to forecast changes to species distributions under future climate scenarios, and the results predict abrupt shifts of dominant tree species in the next decades. Forest diebacks, species migration and displacement, and altitudinal shifts of forest types have already been recorded (Peñuelas & Boada 2003; Allen et al. 2010). For example, in northeast Spain Fagus sylvatica and Calluna vulgaris are being replaced by Quercus ilex at high elevations (Peñuelas & Boada 2003).