Senecio bracteolatus post-fire invasion in a semi-arid grassland: the role of microsites.

FRANZESE J., GHERMANDI L. & BRAN D.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 20 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 comparing these variables between burned and unburned grasslands. In burned areas we compared the abiotic characteristics of two microsites 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 site, seedlings were more abundant under tussock grasses, whereas juveniles were more abundant in gaps. Grasses generated attenuated micro-environmental conditions than gaps during stressful summers. Gaps were more abundant in burned site, while “under tussock” microsites were more frequent in unburned site. In burned areas tussocks allowed greater establishment of seedlings (facilitation), but gaps allowed greater seedlings 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 shrubs seedlings became negative with time probably due to grass competition. Gaps allowed a better perform 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.