Fire cue effects on seed germination of six species of northwestern Patagonian grasslands

Abstract

Abstract. Postfire recruitment of seedlings has been attributed to a stimulation of germination by fire-related cues. The germination response to heat shock (80 • C -5 min), smoke (60 min), the combination of both factors and no heat no smoke (control) was studied in six native species (two dominant grasses, two dominant shrubs and two annual fugitive herbs) of northwestern Patagonian grasslands. Seeds of the grasses Festuca pallescens and Stipa speciosa and the shrub Senecio bracteolatus (Asteraceae) germinated when they were exposed to heat shock, whereas seeds of the other shrub, Mulinum spinosum (Apiaceae), were killed by this fire cue. In grasses, probably the glume of caryopsis protected embryos from heat. Possibly, the seed size could explain the different responses of the two shrubs. Heat combined with smoke reduced seed germination for S. speciosa and S. bracteolatus. The heat could have scarified seeds and the longer exposure to smoke could have been toxic for embryos. The same treatment increased germination of the annual fugitive herb Boopis gracilis (Calyceraceae). We concluded that fire differentially affects the seedling recruitment of the studied species in the northwestern Patagonian grasslands.

Fire as a stimulant of shrub recruitment in northwestern Patagonian (Argentina) grasslands

“…Moreover, when this species was subjected to experimental burning, seedling growth decreased (Franzese and Ghermandi 2012). The germination of F. pallescens was not affected by smoke, heat, or the combination of these factors (Gonzalez and Ghermandi 2012), but experimental burning was shown to reduce the germination and seedling growth of this species (Franzese and Ghermandi 2012). Even though P. speciosa and F. pallescens can resprout after fires, the remaining biomass is very low, and as these species are constantly subjected to grazing, especially by sheep, seedlings and young resprouts can be rapidly eliminated.…”

“…The shrubs M. spinosum and S. bracteolatus are present in low density and are scattered within the grassland matrix. After exposure to fire cues, seeds from M. spinosum were killed and germination of S. bracteolatus seeds was inhibited (Gonzalez and Ghermandi 2012). P. speciosa seeds were shown to increase germination after being exposed to smoke alone (Franzese and Ghermandi 2012) but when the seeds were exposed to a combination of heat and smoke, germination was inhibited (Gonzalez and Ghermandi 2012).…”

“…After exposure to fire cues, seeds from M. spinosum were killed and germination of S. bracteolatus seeds was inhibited (Gonzalez and Ghermandi 2012). P. speciosa seeds were shown to increase germination after being exposed to smoke alone (Franzese and Ghermandi 2012) but when the seeds were exposed to a combination of heat and smoke, germination was inhibited (Gonzalez and Ghermandi 2012). Moreover, when this species was subjected to experimental burning, seedling growth decreased (Franzese and Ghermandi 2012).…”

“…In the last 20 years, many studies concerning the role of fire effects on seed germination have been carried out in fire-prone ecosystems with Mediterranean-type climate (autumn-winter precipitation), such as Australia (Crosti et al 2006;Tieu et al 2001), South Africa (Brown et al 2003), California (Keeley and Fotheringham 1998), the Mediterranean Basin (Moreira et al 2010), and Chile (Figueroa et al 2009;Gó mez-Gonza´lez et al 2008). In northwestern (NW) Argentinian Patagonia, there are few studies on fire cues related to vegetation recruitment (Franzese and Ghermandi 2011;Gonzalez and Ghermandi 2012) notwithstanding the fact that fire, along with grazing, is the main disturbance that affects this region (Gittins et al 2011). Human interventions, as well as the ENSO phenomenon, have changed the fire regime in this region during the last 100 years (Kitzberger et al 2005).…”

Growth and reproductive post-fire responses of two shrubs in semiarid Patagonian grasslands

“…This species forms a transient seed bank: seeds of S. bracteolatus are not found in the seed bank after fire (Gonzalez and Ghermandi 2008). Also seed germination is not stimulated by heat (808C) and smoke treatments (Gonzalez and Ghermandi 2012). Further, Franzese (2006) found that seed production of S. bracteolatus was greater in burned than unburned grasslands 5-6 years after fire.…”