Diversity and functional dynamics affected by drought and fire in Patagonian grasslands

GHERMANDI LUCIANA; GONZALEZ SOFÍA

ECOSCIENCE (SAINTE-FOY)

UNIVERSITE LAVAL

Año: 2009 p. 408 - 417

1195-6860

During 1998-1999 a severe drought occurred in northwestern Patagonia that provoked an extensive wildfire. We monitored vegetation cover and soil seed bank to study the diversity and functional group gap dynamics in burned and unburned sites. Species were grouped in 3 functional groups: forbs, fugitive species and annual grasses. Post-drought vegetation recovered quickly due to a rainy spring in the second year but decreased after a dry and warm spring in the third year. These patterns underline the close relationship that exists between phenological phases and meteorological variables. Drought decreased richness but did not affect the presence of stress-tolerant species, whereas fire increased richness by allowing the establishment of fugitive species. Species in the fugitive functional group are possibly fire adapted and depends on the seed accumulation in the seed bank (storage effect) to coexist with other gap species. Forbs exhibited highest vegetation cover and seed bank density in the unburned site. Global climate change suggests an increase in the frequency and amplitude of El Niño/Southern Oscillation phenomena that, in Northwestern Patagonia, are related to the occurrence of drought, fire and changes in vegetation dynamics.