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

Capítulo 4
(pag 29). In order to characterize better the seed characteristics, seed moisture
content was determined in seeds used to estimate seed dry mass (Appendix S1).
Twenty five experimental plots were set on each of 3 light categories: open
woodlands, beneath cover of Q. ilex, and beneath cover of Q. ilex and simulated shrub
cover. To simulate shrub cover, a green mesh that allowed through 27 % of incident
radiation was placed over the corresponding experimental plots on a rectangular
structure of 2 x 1 m horizontally held on four iron sticks 40 cm over the soil. These light
categories were established to cover a wide range of light availability and to estimate
leaf traits based on light conditions (see below). Each experimental plot was divided in
two replicates (separated 50 cm), so there were 150 replicates in total. Sixteen acorns
(4 per species) were sown at each replicate, 4 cm deep and 5 cm apart in a square grid
of 4 x 4 acorns. Each replicate was protected by a wire square (50 x 50 cm, 1 cm mesh
width), put up and half‐buried to avoid predation by rodents (J. Pausas personal
communication). Weeds were removed by hand during the first spring to avoid
competition.
In each experimental plot, replicates were randomly assigned to an irrigation
treatment (irrigated vs. non‐irrigated). Water was applied during the summer months
of the first year of the experiment (70 days, June – August 2007) at 15‐30 days
intervals. In total, 51 L m ‐2 was added, simulating a rainy summer in this area (data
from Consejería de Agricultura, Junta de Andalucía).
Data collection
The main environmental variables measured that likely influenced seedling
establishment were light availability and soil moisture. The spatial variability of light
was explored with hemispherical digital photography (Rich, 1989). At each plot, a
photograph was taken at the seedling level (about 30 cm over the soil) using a
horizontally‐levelled digital camera aimed at the zenith, using a 180° field of view fisheye
lens. The images were analysed using Hemiview canopy analysis software v 2.1,
which estimates a global site factor (GSF) by combining the proportion of direct and
diffuse radiation. In further analyses this measurement was used as a proxy for light
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