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

Whithin population variability influences early seedling establishment on four Mediterranean Oaks
Data analyses
To investigate the effect of different variables on seedling emergence we used
generalized mixed models (GLMM) with a binomial distribution of errors and a logit
link function, and constructed a model for each species. Seedling emergence was taken
as 1 if plants emerged and 0 otherwise. Experimental plot identity was included as a
random factor to account for the nestedness of the data, and light availability, preemergence
soil moisture, seed mass, mother plant and all two‐way interactions were
taken as the fixed factors. In all cases, seed mass was heavily dependent upon the
mother plant (ANOVA; Q. faginea: R 2 =0.71, P=0.000; Q. ilex: R 2 =0.77, P=0.000; Q.
pyrenaica: R 2 =0.74, P=0.000; Q. suber: R 2 =0.28, P=0.000). To avoid multicollinearity
problems we regressed seed mass against mother tree, and replaced the former
variable with the residuals from the regression (Graham 2003); therefore, the residuals
for seed mass would represent the unique contribution of seed mass, independent
from mother‐induced effects (Castro, 1999).
To detect potential factors influencing time to emergence in each Quercus
species we used Linear Mixed Models (LMM), in which experimental plot identity was
included as a random factor, to account for the structure of the data. As fixed factors
we considered the same variables as above, and all two‐way interactions.
To analyse seedling survival in two successive years after plantation and
establishment success at the end of the experiment we built binomial generalized
mixed models (GLMM) for each species. Seedling survival was taken as 1 if emerged
seedlings were alive and 0 otherwise, and establishment success was coded as 1 for
those seedlings found alive at the end of the experiment and 0 for those plants dead
or not even emerged. In all cases, experimental plot identity was included as a random
factor to account for the structure of the data. Light availability as measured through
GSF, residuals of seed mass (see above), mother plant, irrigation treatment, and all
two‐way interactions were taken as the fixed factors. For models in year 1, soil
moisture in spring was also included to reflect early growth conditions.
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