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

Spatial and temporal heterogeneity effects on seedling growth and establishment in four Quercus species
in the former. Therefore, water was seemingly a more limiting factor in plot 2, with
especially dry zones where all species were bound to exhibit a high mortality.
Growth and morphology
Unexpectedly, growth‐related variables exhibited virtually no aggregation
patterns. Laliberté et al. (2008) found the spatial patterns for stem diameter and
height to account for a very low fraction of the overall variance. Pérez‐Ramos et al.,
(2010) found growth of Quercus seedlings during the first year to depend more
markedly on the seed reserves than on the environmental conditions, as seedlings
have a limited photosynthesis capacity during these first stages. In our study, seed
mass was the main factor explaining morphology and growth variance, and it was
especially important on plot 1. Seed‐mass represents the amount of reserves available
for growth development on the first stages of seedling development. Larger seed‐mass
is related to a larger seedling biomass, which confer some advantages on seedling
stablishment (Hendrix et al., 1991; Chacón and Bustamante, 2001).
In general, variance explained in all models was not very high. Pérez–Ramos et al.
(2010) found similar values for first year growth in Quercus species, and models fit
increased in the second year, in which environmental variables were more explicative.
As noted above, it seems that during the first year seedlings are more dependent of
intrinsic characteristics as seed‐mass or other factors such as seed chemical
composition no contemplated in this study but which could be more critical (Villar‐
Salvador et al., 2009).
Although environmental variables explained less variance than seed mass, they
were selected as predictors in many models in plot 2 whereas they were just included
in one model of plot 1. This confirms the high variability in Mediterranean ecosystems,
where, as we have seen, resources availability may change in few meters, determining
two areas very closed each other but in which seedling performance was different.
Light availability is an important resource which determines species distribution
in Mediterranean environments (Beckage and Clark, 2003; Zavala and Zea, 2003).
However, it doesn´t appear as a key factor explaining Quercus growth variability. This
may be caused by the fact that growth of large seeded species is less responsive to
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