Waterbird detritus impair seedling root growth in a unique centenarian cork oak population: implications for forest regeneration
Abstract: Field studies have shown than soil-mediated effects of nesting wading birds may be a main cause of the decline of centenarian cork oaks (Quercus suber L.) in the Doñana Biological Reserve (SW Spain). The aim of this work was to experimentally investigate whether soil modification by bird detritus significantly affected the first stages of development of Q. suber. Seedlings were growing under controlled conditions in three types of natural soils with different levels of wading bird influence. Our results showed that main root length was strongly reduced by bird influence. Bird-influenced soils significantly decreased both the above-ground and the below-ground seedling dry biomass. Guano seems to harm primary root meristem stopping the main root growth, which becomes thickened (root stunting). This impedes the quick initial main root growth that this species usually exhibits prior to shoot emergence. Since the presence of a well-developed main root is essential to explore deep soil layers and extract additional water over the dry season, we predict that guano-affected seedlings will suffer a higher mortality in summer. We concluded that even low levels of wading bird influence could strongly hamper cork oak regeneration in the studied area. Thus, both natural and assisted cork oak regeneration will fail in these bird-influenced soils.