Branch architecture in relation to canopy positions in three Mediterranean oaks.

Branch architecture is a key determinant of plant performance owing to its role in a light interception by photosynthetic tissues. However, under stressed conditions, excess light may be harmful to the photosynthetic apparatus, and plants often present structural mechanisms to avoid photoinhibition. Three-dimensional models were constructed of the aerial parts in different locations within the crown of three co-occurring tree species (Quercus ilex, Q. suber and Q. faginea) growing in a Mediterranean environment. We hypothesized that the species with the shorter leaf life span would exhibit higher leaf display efficiency (silhouette to total leaf area, STAR), maximizing light interception and photosynthesis in the short term. In addition, more exposed positions within a canopy should develop more structural avoidance mechanisms to minimize excessive radiation. Significant differences were detected in architectural traits at both the intra- and interspecific level. Architectural traits promoting greater self-shading were more frequent in the species with longer leaf longevity and in the canopy locations experiencing higher temperatures at the times of maximum sunlight. However, these trends were in part counteracted by the changes in individual leaf area, which tended to be larger in the species with shorter leaf longevity and in the less exposed canopy locations. We conclude that the variation in architectural traits occurs mainly as a means to avoid the excessive self-shading of branches with the largest leaf size.