Postfire shrub recruitment in a semi-arid grassland: the role of microsites

FRANZESE JORGELINA; GHERMANDI LUCIANA; BRAN DONALDO

JOURNAL OF VEGETATION SCIENCE

Opulus Press

Lugar: Grangärde; Año: 2009 p. 251 - 259

1100-9233

Question: (1) Which factors regulate postfire recruitment and spread of Senecio bracteolatus shrub in Patagonian grasslands? (2) What is the role of Stipa speciosa grass on S. bracteolatus establishment in the postfire succession? Location: Northwestern Patagonian grassland, Argentina. Methods: We studied the effect of fire on S. bracteolatus recruitment and density by comparing these variables between burned and unburned grasslands. In burned areas we compared abiotic characteristics and seedling establishment under tussock grass canopy (S. speciosa) and in gaps (inter-tussock areas). Postfire interactions between S. bracteolatus seedlings and S. speciosa were studied with field and greenhouse experiments. Results: Density of S. bracteolatus was higher in burned than in unburned areas. In burned sites, seedlings were more abundant under tussock grasses, whereas juveniles were more abundant in gaps. Grasses generated more attenuated micro-environmental conditions than gaps during stressful summers. Gaps were more abundant in burned sites, while “under tussock” microsites were more frequent in unburned sites. In burned areas, tussocks allowed greater establishment of seedlings (facilitation), but gaps allowed greater seedling growth and greater persistence of juveniles. Conclusions: Fire promoted S. bracteolatus recruitment in Patagonian grasslands by increasing the availability of favourable gap microsites. The positive condition for shrub seedlings became negative with time, probably due to grass competition. Gaps led to better performance and persistence of shrub plants. Six years after fire, greater shrub recruitment and adult density (observed as a trend) in burned grassland provide an opportunity for potential S. bracteolatus invasion.