Early post-fire succession in northwestern Patagonia grasslands

Abstract

Large-scale disturbances, notably fire and grazing, structure grass and shrubland dynamics in semi-arid environ- ments. We studied early post-fire succession in two burned grasslands, one unburned grassland, and one shrubland near the burned area. We observed three processes: (1) establish- ment of a 'phantom' community comprised of fugitive species. Although transient, these species increase diversity and re- charge the seed bank before the next disturbance; (2) regenera- tion of the original community by persistence of resprouter species and by auto-replacement; (3) early stages of invasion by seedlings of the shrub Fabiana imbricata, which germinate next to shrubland and create new F. imbricata patches. Weed invasion was principally due to the ruderal exotic species Verbascum thapsus from the nearby road verge and by rapid increase of Rumex acetosella cover, another exotic species present before the fire. Although post-fire climatic condi- tions are particularly important in semi-arid environments, succession depends greatly on the regeneration strategies and dispersal abilities of the species present in the burned area. The phantom community occurs only at the first stage of succession when there is little competition for resources. We could call this process 'the race for occupation of the area'. The second stage, when competition for resources becomes progressively more important, could be called 'the effort to maintain space'.