Post‐fire shrub recruitment in a semi‐arid grassland: the role of microsites

Abstract

Question: (1) Which factors regulate post‐fire recruitment and spread of the shrub Senecio bracteolatus in Patagonian grasslands? (2) What is the role of the grass Stipa speciosa on S. bracteolatus establishment in the post‐fire succession? Location: Northwest Patagonia, 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 the canopy of grasses (S. speciosa) and in gaps (inter‐tussock areas). Post‐fire interactions between S. bracteolatus seedlings and S. speciosa were studied using 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. Tussocks 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 higher establishment of seedlings (facilitation), but gaps allowed more seedling growth and higher persistence of juveniles. Conclusions: Fire promoted S. bracteolatus recruitment in Patagonian grasslands by increasing the availability of favourable gap microsites. Grass protection for shrub seedlings became negative with time, probably due to competition with grasses. Gaps led to better performance and persistence of shrub plants. Six years after fire, higher shrub recruitment and adult density (observed as a trend) in burned grassland provides an opportunity for potential S. bracteolatus invasion.

Are Fabiana imbricata shrublands advancing over northwestern Patagonian grasslands? A population dynamics study involving fire and precipitation

“…Given that F. imbricata is unpalatable, environmental value as a production unit might diminish because of its advance. Several previous studies suggest that fire can promote shrub invasion in the Patagonian steppe (Franzese et al, 2009;Ghermandi et al, 2004Ghermandi et al, , 2010Gonzalez et al, 2010). In early post-fire succession, new encroachment foci of F. imbricata were observed (Ghermandi et al, 2004).…”

“…Plants show variable responses to these variations which regulate their population dynamics. Many species are stimulated by fire, which increases their germination and seedling recruitment (Bond and van Wilgen, 1996;Franzese et al, 2009;Ghermandi et al, 2004Ghermandi et al, , 2010Pausas et al, 1999) to the point that, for some species, reproduction has a forced dependence on fire and they can be driven to extinction by fire suppression (Bond and van Wilgen, 1996).…”

Effect of fire on recruitment of two dominant perennial grasses with different palatability from semi-arid grasslands of NW Patagonia (Argentina)

“…The temperatures selected were within the temperature range that seeds buried in the superficial soil layers experience during grassland fires (Wright and Bailey 1982). We exposed the seeds to dry heat, because fires occur during summer when the superficial soil is dry (Franzese et al 2009). For the smoke treatment, seeds were exposed to smoke for 10 min (Pérez-Fernández and Rodríguez-Echeverría 2003).…”

Deadwood anisotropic facilitation on seedling establishment after a stand-replacing wildfire in Aosta Valley (NW Italy)

“…This is particularly evident in climatically stressed sites, where seedlings establishment is strongly limited by harsh conditions. Mature plants, shrubs, deadwood or rocks can play a positive role in ameliorating microsites along with surface microtopography (Castro et al, 2002;Resler et al, 2005;Franzese et al, 2009;Beghin et al, 2010;Legras et al, 2010). Especially in water stressed/limited environment these elements can reduce soil temperature (shading effect) and wind (less transpiration), and increase relative humidity (Flores and Jurado, 2003;Castro et al, 2011).…”