The performance of Mediterranean subshrubs depends more on microsite than on regional climate conditions.

摘要

Question: To what extent do small-scale biotic interactions and local variations determine the spatial pattern and plant performance of three Mediterranean subshrubs growing under contrasting climatic conditions Location: Three sites subjected to climatically contrasting conditions in Aragon (Javalambre, cold site; Bernues, mesic site; Monegros, xeric site), NE Spain. Methods: The three species studied were Hormathophylla spinosa, Ononis fruticosa and Linum suffruticosum in the cold, mesic and xeric sites, respectively. Two transects (100x5 m) were located in each site, one in the upper part and another in the north-oriented slope of a hill. All adult individuals located within each transect of each species were tagged, spatially located and their size measured (height and crown diameter). We also estimated visually the cover of other woody species around each subshrub individual to study inter-specific interactions. We estimated the age of all subshrub individuals by counting annual rings in basal wood sections. To investigate the spatial patterns and plant performance of the three species we used spatial point pattern analyses and structural equation modelling. Results: The density of individuals and the spatial pattern of the species varied greatly among and within sites. H. spinosa and L. suffruticosum showed higher variability in density among transects and a more aggregated spatial pattern than O. fruticosa. Similarly, the three subshrubs presented different architecture and performed differently in the two transects studied for each species. All three species presented higher growth rates in the upper part of the hill than in the north-oriented slope. Inter-specific interactions were more important than intra-specific ones in determining the performance of the three subshrubs, and were more intense in the case of H. spinosa and L. suffruticosum than in the case of O. fruticosa. Conclusions: Our results demonstrate that the spatial patterns of the three species studied varied within sites as a function of local environmental conditions. Moreover, plant-plant interactions can play an important role in explaining subshrub spatial patterns and performance in Mediterranean ecosystems. Inter- and intra-specific interactions acting at local scales should be considered for understanding the responses of Mediterranean subshrubs to regional climate.