Shifts in the regeneration niche of an endangered tree (Acer opalus ssp granatense) during ontogeny: Using an ecological concept for application

Most of our knowledge regarding ontogenetic niche shifts in plants has been derived from studies involving only two or unconnected life stages. Approaches covering a broader range of different life stages are still needed to fully understand the implications of ontogenetic niche shifts for plant regeneration dynamics. We investigated ontogenetic shifts in the endangered Mediterranean tree species Acer opalus ssp. granatense (A. opalus) comparing the environmental characteristics of individuals of different ages with those of a random sample of available microsites. In addition, since herbivory could be limiting factor, herbivory damage was quantified. Differences in environmental characteristics between locations of individual plants and randomly selected points became larger with plant age. suggesting that the regeneration niche of A. opalus shifts during ontogeny, undergoing a contraction. The presence of shrubs and adult trees, the depth of the litter layer, and herbivory were the main factors influencing these changes. A. opalus can germinate in all available microhabitats its seeds can reach, but samplings establish and grow only in a subset of microhabitats, which represent a change in tolerence to extrinsic factors. Old saplings establish under the canopy of shrubs, far away from tree cover that could block light required in the oldest stage. Therefore, temporal changes in the nature and strength of plant-plant interactions are also occuring. The ecological concept of niche shifts reveals the microsites with higher probabilities of long-term sapling survival of A. opalus: shurb cover involves an array of environmental changes crucial for the successful establishment of A. opalus saplings under stressful Mediterranean conditions, from microhabitat amelioration to herbivory protection. (c) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.