Introduction

Forests provide a range of goods and services upon which humanity depends, from local (e.g. flood prevention) to global (e.g. carbon sequestration). Yet some 13 Mha of forest is lost each year, mostly in the tropics (Canadell & Raupach 2008). Considerable political, media and scientific attention has focused on this forest destruction and fragmentation and its implications for livelihoods, biodiversity and ecosystem services. However, human influences on forests now go beyond deforestation and degradation, to changing the states of atmosphere and climates and altering biogeochemical cycles, which in turn bear heavily on the functioning and composition of forest ecosystems. A range of disciplines are required to chart such change, understand how it works and predict where it is going. They span a broad range of scales from photosynthetic machinery in leaves, to the dynamics of forests across wide regions, to global atmospheric circulation. Integration of these multiple strands and scales of investigation has only recently begun, and this volume makes an important contribution to weaving them together into a more cohesive, albeit still incomplete, picture.

The story is told in three parts, beginning with a collection of perspectives on the global environmental drivers of forest change, the complexity of their interaction and effects, and important feedbacks. The second section concentrates on species-level traits and trade-offs, and how these explain the composition and dynamics of forests in a changing world. Finally, a number of approaches and tools are presented for measuring forest change and forecasting its future direction.

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).