Early post-fire succession in northwestern Patagonia grasslands

Abstract

Large-scale disturbances, notably fire and grazing, structure grass and shrubland dynamics in semi-arid environments. We studied early post-fire succession in two burned grasslands, one unburned grassland, and one shrubland near the burned area. We observed three processes: (1) establishment of a 'phantom' community comprised of fugitive species. Although transient, these species increase diversity and recharge the seed bank before the next disturbance; (2) regeneration of the original community by persistence of resprouter species and by auto-replacement; (3) early stages of invasion by seedlings of the shrub Fabiana imbricata, which germinate next to shrubland and create new F. imbricata patches. Weed invasion was principally due to the ruderal exotic species Verbascum thapsus from the nearby road verge and by rapid increase of Rumex acetosella cover, another exotic species present before the fire. Although post-fire climatic conditions are particularly important in semi-arid environments, succession depends greatly on the regeneration strategies and dispersal abilities of the species present in the burned area. The phantom community occurs only at the first stage of succession when there is little competition for resources. We could call this process 'the race for occupation of the area'. The second stage, when competition for resources becomes progressively more important, could be called 'the effort to maintain space'.

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

“…Our experimental results did not explain the massive postfire seedling recruitment observed of fugitive species in the field (Ghermandi et al, 2004). Probably, seed germination of the studied species is widely stimulated by other levels and periods of exposure to temperature and smoke, which were not tested in this study.…”

“…B. gracilis and N. linearis are fugitive herbs, which recruit in great abundance after fires but drastically reduce their cover one year later (Ghermandi et al, 2004).…”

“…Resprouting plants replace the biomass removed by fire from surviving aboveor below-ground dormant meristems, whereas non-sprouting species are killed by fire and depend on seed for persistence (Bond and van Wilgen, 1996). 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.…”

“…Fires normally occur during dry summers and the burned areas can be extensive because dominant vegetation accumulates large amounts of fast-drying fuel and their spatial continuity favors fire spread (de Torres Curth et al, 2008). However, these grasslands are resilient because of the fast regrowth of grasses and shrubs and seedling recruitment from the seed bank (Ghermandi et al, 2004). Fire is often caused by lightning; however fire occurrence of anthropogenic origin has increased in recent years (de Torres Curth et al, 2008).…”

Grazing Effects on Vegetation Composition and on the Spread of Fire on Open Sand Grasslands

“…Grazing and fire regimes are the most important large-scale disturbances on semiarid and arid grassland communities (van Langevelde et al, 2003;Ghermandi, Guthmann, and Bran, 2004;Feldman and Lewis, 2005). In most cases, fire and herbivory are independently investigated (Archibald, Bond, Stock, and Fairbanks, 2005), although more and more recent studies have examined these two disturbances together (Collins, 1987;Belsky, 1992;Noy-Meir, 1995;Boer and Stafford Smith, 2003;Harrison Inouye and Safford, 2003;Fuhlendorf and Engle, 2004;Fynn, Morris, and Edwards, 2005;Archibald et al, 2005).…”