A resprouter herb reduces negative density-dependent effects among neighboring seeders after fire

Plant communities are often composed of species belonging to different functional groups, but relatively few studies to date have explicitly linked their spatial structure to the outcome of the interaction among them. We investigated if mortality of seeder species during their establishment after fire is influenced by the proximity of the resprouter herb Brachypodium retusum. The study was conducted in a Mediterranean shrubland (00°39′ W; 38°43′ N), 40km northwest of Alicante (Spain) with Ulex parviflorus, Cistus albidus, Helianthemum marifolium, and Ononis fruticosa as dominant obligate seeder species and a herbaceous layer is dominated by the resprouter B. retusum. We followed the fate of mapped seedlings and the biomass of B. retusum one, two, three and nine years after an experimental fire. We used point pattern analyses to evaluate the spatial pattern of mortality of seeder species at these years in relation to the biomass of B. retusum. We hypothesize that B. retusum may initially have a positive impact on seeder survival. We implemented this hypothesis as a point process model that maintains the overall number of dead seeder plants, but seeder survival varied proportionally to the biomass of B. retusum in its neighborhood. We then contrasted this hypothesis with a previous analysis based on a random mortality hypothesis. Our data were consistent with the hypothesis that proximity of B. retusum reduced the mortality of seeder plants at their establishment phase (i.e., 2 yrs after fire). However, we found no evidence that B. retusum influenced seeder mortality when plants grow to maturity. We also found that, under the more stressful conditions (fire+erosion scenario), B. retusum had a lower impact on the performance of seeder species. Our results suggest that B. retusum may reduce negative density-dependent effects among neighboring seeder plants during the first years after fire.