Abstract
In Mediterranean environments, light and water are clearly dominant ecological drivers of seedling growth and survival, and their interaction could modify productivity and forest composition. We examine the early response of seedlings of four co-occurring Mediterranean tree species (Pinus pinea, Juniperus thurifera, Quercus ilex and Quercus faginea) grown in the nursery to differing light and water availability conditions. Morphological (survival, height, biomass) and physiological (shoot midday water potential, net photosynthesis, transpiration rate, stomatal conductance, Fv/Fm, PSII and ETR) traits were studied, along with biomass allocation traits and drought resistance and plasticity indices. A significant effect of both factors was mainly shown for growth and morphological traits, while survival, physiological traits and allometry were affected by either water availability or light, being more remarkable the effect of water availability over light. Drought severely limited Q. faginea’s survival under both light intensities. The high plasticity of J. thurifera and Q. ilex seedlings to different light and water availability environments will confer these two species with an adaptive advantage in the early growth stages in comparison with P. pinea and Q. faginea seedlings. Thus, to maintain the codominance of the four species, silvicultural interventions should focus on the joint management of all of them.
Highlights
Light and water availability at stand level are environmental factors that greatly conditioned survival, growth and regeneration dynamics of forest species [1,2,3]
At the end of the experiment, seedlings grown under shade conditions and high water availability (W+L−) were the tallest for all species except for Q. faginea, which was tallest at full light conditions and high
At the end of the experiment, seedlings grown under shade conditions and high water availability (W+L−) were the tallest for all species except for Q. faginea, which was tallest at full light conditions and high water availability (W+L+) (Figure 3)
Summary
Light and water availability at stand level are environmental factors that greatly conditioned survival, growth and regeneration dynamics of forest species [1,2,3] Their interactive effect occurs in a great variety of site conditions [4], and could modify productivity and forest composition [5]. The complex interactions and trade-offs between light and water availability have helped to determine the optimal regeneration niche of a wide range of forest species [6,7,8,9] Understanding how such interactions affect seedling performance will be especially relevant in those regions that show a marked drought season and that are highly sensible to the effects of climate change [10]. The projection of more frequent, longer, severe summer droughts and heat waves in the Mediterranean region (e.g., [12,15]) will hinder the successful establishment of tree seedlings in the short term and the regeneration of the stand in the long term
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