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

Capítulo 3
aggregation; on the other hand, in especially dry years survival is usually too low for
any aggregation to be observed. Therefore, experimental designs and statistical
analyses should consider the above‐described spatial and temporal heterogeneity
(Legendre, 1993; Zas, 2006) in order to accurately assess the influence of some key
factors influencing early recruitment stages. Although an increasing number of
spatially explicit experimental designs is being used to examine aggregation patterns
for recruitment‐related variables (Maestre et al., 2003; García and Houle, 2005; Quero,
2007a), few authors have applied them simultaneously to several philogenetically
related species.
Moreover, no study appears to have so far been conducted to establish the
aggregation patterns for morphological and growth related variables in seedlings (but
see Laliberté et al., 2008), which might have an impact on plant establishment.
Seedling growth rates are very often influenced by environmental factors (Poorter,
2001; Villar et al., 2008); therefore, changes in such factors along spatial and temporal
gradients might lead to the presence of areas with bigger or faster growing seedlings.
In addition to environmental factors, some intrinsec traits as seed mass determine
early seedling performance (ver capítulo 5). Experiments that evaluate seedling growth
have been typically carried out under controlled conditions, and field experiments use
to limit growth measures just to seedling height (Beckage and Clarck, 2003; Laliberté et
al., 2008). However, it is necessary to contrast the results and conclusions of this kind
of works with more complete field studies (Pérez–Ramos et al., 2010) in which more
morphological traits were involved.
The genus Quercus is widely represented in the Mediterranean basin. Evergreen
species are abundant in the semi‐humid Mediterranean mountains of southern Spain;
by contrast, semi‐deciduous and deciduous species are scantier and occupy microsites
with higher water availability owing to their lower drought tolerance (Acheral and
Rambal, 1992; Carrión et al., 2000, Urbieta et al., 2008b). Moreover, deciduous oaks
usually have higher leaf areas and growth rates than evergreens (Ruiz Robleto and
Villar, 2005; Quero et al., 2006).
77