PARENT SESSION
Poster Session 11: Disturbance Ecology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Shrub encroachment in a temperate savanna (Argentina): Responses to fire and herbivory in two dominant Asteraceae species.
Guadalupe, Galíndez*,1, Fernando, Biganzoli1, Cristian, Pereyra1, Ana , Scopel1, 1 IFEVA-CONICET. Facultad de Agronomía. Universidad de Buenos Aires. Av. San Martín 4453., Capital Federal, Argentina
ABSTRACT- Over the last decades and concomitantly with changes in the disturbance regime (i.e., fire and herbivory), temperate savanna of eastern Argentina has experienced a significant increase in the abundance of native shrubs. We set up a factorial experiment to study the responses of Baccharis dracunculifolia and Eupatorium buniifolium, the two dominant species, to fire (burned/unburned) and herbivory (grazed/ungrazed). During 2001-2003 we monitored: survival, growth, seed production and seedling establishment. Burning and grazing had a negative effect on B. dracunculifolia population in terms of survival; all juvenile and mature plants died at the end of the study. In contrast, 80-100% of E. buniifolium individuals (juvenile and mature) survived after fire due to their high resprouting capacity. However, in grazed treatments, all juvenile plants were consumed by grazing. Plant growth was significantly higher in burned than unburned treatments. Seed reproduction was significantly lower in burned and grazed than in unburned/ungrazed treatments. Although seedling emergency was low in burned and grazed areas for both species, < 8 and 25 seedlings/100 m2, for E. buniifolium and B. dracunculifolia, respectively, 50-100 % survived at the end of the experiment. Mortality was higher in grazed areas and all B. dracunculifolia that survived were associated with other species. Results indicate that both fire and grazing, rather than a single factor, control the population dynamics of these two species. This suggest that a decrease in fire frequency and/or alleviation of grazing pressure would result in an increase in shrub abundance. These predictions are in agreement with the changes in disturbance regime that these savannas have experienced over the last decades.
Key words: temperate savanna, shrub encroachment, fire and herbivory, Argentina