Herbivory has a greater impact in shade than in sun: response of Quercus pyrenaica seedlings to multifactorial environmental variation

Many biotic and abiotic factors affect seedling establishment in woody plants. In Mediterranean environments, the major factors affecting tree regeneration are light, water, and herbivory. We investigated the response of some morphological and chemical traits of Quercus pyrenaica Willd. seedlings to simulated herbivory (hand removal of 50% of the aerial mass) and two levels of light (sun vs. shade) and water (one vs. two waterings). Water had no appreciable direct effect on morphological or chemical traits. Shaded seedlings grew less but had greater total leaf area. Simulated herbivory decreased the total leaf area, and root and aerial mass. Among the chemical characteristics, shaded seedlings had higher levels of nitrogen and lower levels of condensed tannins. In colorimetric assays of tannins, clipped seedlings had lower absorbances than did unclipped plants, and this effect was more pronounced in the sun than in the shade. Our experiment shows that light availability and herbivory affect the development and defence of Q. pyrenaica seedlings. Although Q. pyrenaica tolerated shade and simulated herbivory, both factors decreased biomass and chemical defence, which could affect the seedlings' future performance.