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

S L Gonzalez,L Ghermandi

doi:10.5194/nhess-12-2753-2012

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.

Highlights

In fire-prone ecosystems, many plants have developed regeneration mechanisms which allow them to survive fire and persist in time (Whelan, 1995)
Fire-related cues did not affect seed germination of the grasses (P > 0.05) (Fig. 1a and b), the germination of Stipa speciosa was somewhat lower when seeds were exposed to Heat + Smoke treatment (Fig. 1b)
Senecio bracteolatus seeds showed that decrease of the germination for the combined treatment was significant (P < 0.05) (Fig. 1c)

Summary

Introduction

In fire-prone ecosystems, many plants have developed regeneration mechanisms which allow them to survive fire and persist in time (Whelan, 1995). In the first postfire growing season, massive seedling recruitment of seeder shrubs and fugitive species from the soil seed bank is commonly observed (Ghermandi et al, 2004; Keeley et al, 2005). The latter species occupy the site temporarily and their abundance normally decreases in subsequent years. Some studies from chaparral and tropical savannas showed that the combination of heat shock and plant-derived smoke can produce a decrease in germination (Keeley and Fotheringham, 1998; Williams et al, 2003). Seeds in the soil experience a combination of several cues during and after fire, but their germination response to the combination of heat shock and smoke is not well understood (Thomas et al, 2007)

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