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

Capítulo 4
environmental extremes. This can be related to an opportunistic exploitation of
resources that allows germination when minimal favourable conditions are met.
Across species, Q. faginea and Q. pyrenaica emerged before the evergreen
species. Urbieta et al. (2008a) found the same effect for deciduous oaks in a similar
field experiment, and it was also observed in a green‐house experiment using acorns
from the same sources (VGR, unpublished data). Thus, emergence date appears to be a
species‐specific character (Laliberté et al., 2008) that can be modified by maternal
source.
Surprisingly, the probability of acorn emergence was not explained by
environmental factors but only by intrinsic characteristics: maternal origin and seed
mass. Although other studies have described the effects of environmental factors on
emergence, most of them overlooked intrinsic factors related to maternal origin (Tyler
et al., 2008; Mendoza et al, 2009). Urbieta and co‐workers (2008a) accounted for seed
mass in explaining probability of emergence in oaks and found no influence of seed
mass on emergence rates, but their results might be unduly affected by extreme local
conditions such as winter flooding that prevented seedling emergence. In the same
sense, planting year has also found to be a crucial agent impacting emergence rates
due to rainfall variability (Tyler et al., 2008). In our case, suitable light and temperature
conditions in spring 2007 may have not limited seedling emergence that was thereby
more dependent on seed characteristics. Seed mass benefits on seedling emergence
have been previously reported (Winn, 1985; Seiwa, 2000). On the other hand, the
relationship between seed mass and emergence may only hold for some maternal
plants according to a similar essay with Scot pine (Castro, 1999). We found this effect
for Q. ilex, for which mother tree determined a positive or negative effect of seed mass
on emergence probability. On the other hand, Q. ilex had the lowest emergence rates.
Since there were no predation signs, this limitation could be caused by a higher
susceptibility to desiccation (Kollmann and Schill, 1996; Smit et al., 2009) or other
uncontrolled factors. Acorn genetic variability and physiological status may also have
an impact on germination and emergence rates (Merouani et al., 2001; Goodman et
al., 2005).
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