Fire responses of three co-occurring Asteraceae shrubs in a temperate savanna in South America

Abstract

South American temperate savannas have undergone significant woody plant encroachment through changes in their disturbance regimes. We studied fire strategies and the spatial variation in individual fire responses of Eupatorium buniifolium, Baccharis medullosa and B. dracunculifolia, the dominant shrub species at El Palmar National Park, in areas with different fire history. In recently burnt sites, all Baccharis dracunculifolia individuals died, whereas all E. buniifolium and B. medullosa individuals sprouted. The relative growth rate was higher in E. buniifolium, which invested more biomass in shoots, and in B. medullosa, which invested more biomass in leaves. At the unburnt site, B. dracunculifolia showed the highest growth rate and leaf biomass. B. medullosa produced capitula immediately after fire, whereas E. buniifolium reproduction was delayed for 1 year. In both species, production of capitula and reproductive effort were higher in recently burnt sites. For B. dracunculifolia, production of capitula was lower and the reproductive effort was higher in burnt than in unburnt sites. Seedling establishment was extremely low for E. buniifolium, low for B. medullosa and high for B. dracunculifolia in both recently burnt sites. E. buniifolium behaved as a sprouter, B. medullosa as facultative sprouter and B. dracunculifolia as obligate seeder species. In order to control the increase and/or attain desirable population levels of these species, fire management practices in these savannas should consider individual species' responses, particularly to the time since the last fire.