Establecimiento de cuatro especies de Quercus en el sur de la ...

Whithin population variability influences early seedling establishment on four Mediterranean Oaks
INTRODUCTION
A vast proportion of the forested areas in temperate and subtropical regions of
the Northern Hemisphere are dominated by species belonging to Quercus genus
(Pulido, 2002). Traditional land uses (i.e. agriculture and cattle rising) have dramatically
reduced or deeply altered forested areas. Coupled with these management practices,
climatic and environmental factors determine a very limited regeneration with very
low seedling establishment and fast ageing populations. In Mediterranean areas, oak
forests are one of the main ecosystem types. The Mediterranean climate is
characterized by large intra and inter‐annual variations in environmental conditions
(Blondel and Aronson, 1995). In addition, resource availability may change spatially,
and it is also distributed across gradients that determine a great variability of
combinations of different factors (Sack and Grubb, 2002; Gallardo, 2003). Plant species
have to cope with this spatial and temporal heterogeneity, which is especially
important in the first stages of establishment, when seedlings are especially sensitive
to environmental conditions (Pulido, 2002). Multiple factors constrain the
establishment of woody seedlings at its first phases in Mediterranean areas. Summer
drought is known as a major cause of mortality (Herrera et al., 1994) and its impact is
likely to increase in the Mediterranean area under a climate change scenario (Peñuelas
et al., 2004). Rainy summers may thus represent a recruitment opportunity, especially
in species less tolerant to hydric stress (Mendoza et al., 2009). Another limiting factor
for growth and survival is light availability, whose spatial gradient determines niche
differentiation along successional stages (Beckage and Clark, 2003). Many studies have
demonstrated that moderate shade benefits seedling survival by protecting against
excessive evapotranspiration and photo damage caused by high radiation (Puerta‐
Piñero et al., 2007; Gómez‐Aparicio et al., 2008).
It has been proposed that maintaining high phenotypic diversity may be crucial
for species inhabiting in such unpredictable and heterogeneous environments
(Sánchez‐Vilas and Retuerto, 2007). In this way, the study of adaptive variation within
and among populations is necessary to understand how species deal with local
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