PARENT SESSION
Poster Session: Ecological Impacts of Invasive Plants
Tuesday, November 4, 2003, 5:00 PM to 7:00 PM
Global Ballroom

The impact of exotic grasses on the biodiversity of Brazilian savannas.

Pivello, Vania^*,1, ¹ Universidade de Sao Paulo, Sao Paulo, SP, Brazil

ABSTRACT- Exotic grasses - especially C4 African species - brought to Brazil as cattle forage found in the savanna region ("cerrado") favorable conditions to grow. Several became cerrado invaders and are threatening its natural biodiversity. Today, African grasses are present in every cerrado patch, including the nature reserves. The frequency, density, vigor, dominance and importance of native and alien herb species were analyzed in two cerrado reserves (Emas Cerrado and Pe-de-Gigante Cerrado, Sao Paulo, Brazil) aiming at comparing the abundance and importance of alien grasses against the native species in the communities, and also identifying spatial distribution patterns of the aliens. Herb species were sampled along border-to-center transects. Interspecific associations among the most abundant species were tested (chi-square and Spearman tests). In both reserves the African grasses Melinis minutiflora Beauv and Brachiaria decumbens Stapf scored very high values of importance. At Emas Cerrado, M. minutiflora was the second and B. decumbens the third most important species. At Pe-de-Gigante Cerrado, two physiognomies were analyzed. M. minutiflora was the most important in one physiognomy, and B. decumbens was the second in the other. Interspecific associations among these aliens and some native grasses resulted strongly negative suggesting an exclusion effect of them over the natives. Although both M. minutiflora and B. decumbens were more abundant in cerrado fragments borders, they showed different spreading strategies to establish on a new environment. M. minutiflora moves through disturbed plots and track borders while B. decumbens establishes as a monospecific belt from the fragment border to its center.

Key words: cerrado, African grasses, savanna, Brazil