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

Whithin population variability influences early seedling establishment on four Mediterranean Oaks
Survival
Mediterranean climate is characterised by large water deficits in which
belowground resources are more critical than light or other environmental factors
(Retana et al., 1999; Coomes and Grubb, 2000; Maltez‐Mouro et al., 2007). In fact,
irrigation was the main factor that explained survival after the first summer for all
species. The benefit of an extra amount of water during the dry period has been
largely demonstrated on Mediterranean environments (Castro et al., 2005; Gómez‐
Aparicio et al., 2008; Mendoza et al., 2009). Indeed, rainy summers represent a
recruitment opportunity for species growing in semi‐arid ecosystems. Interestingly,
when irrigation was not taken into account, maternal origin had a prime role in the
survival of all species except Q. faginea. This result suggests that the effects of
maternal source can be masked under the ameliorated conditions simulated by
summer irrigation. In this sense, under extreme environmental conditions, such as the
severe drought that occurred during the experiment (just 3 mm of precipitation during
the 3 summer months), maternal traits are the main factors determining survival.
Other factors were implied in first‐year survival of Q. suber, maybe showing the
weaker effect of irrigation for this species that has been previously reported (Gómez‐
Aparicio et al., 2008). Depending on mother tree, radiation negatively affected Q.
suber survival. Moderate shade provided by shrubs or trees creates a suitable
microhabitat for recruitment that protects seedlings from excessive evapotraspiration
(Puerta‐Piñero et al., 2007; Gómez‐Aparicio et al., 2008). This beneficial effect of shade
was probably overwhelmed for the other species in our study by soil water availability
because the summer of the experiment was exceptionally dry. Indeed, under nonirrigation
conditions, survival of Q.suber depended on spring soil moisture, as well as
on intrinsic parameters (seed mass and maternal traits).
Different effects explained survival after second summer for each Quercus
species. Irrigation had a delayed effect only in two of the four species studied and
interestingly, this effect varied across mothers. For these species, seedlings that
survived the first year due to an increased water supply were able to survive in the
second year, maybe because during the second growing season they could develop
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