Consequências da alteração do hábitat para a dispersão e predação de sementes de Cavanillesia arborea (Malvaceae) em florestas tropicais secas

Abstract

We compared these processes in pasturelands and preserved old-growth forests in the Mata Seca State Park and its surroundings. To describe the seed shadows, 15 isolated individuals of C. arborea were marked in each habitat type and seed density was determined up to a 30 m radius from each parental plant. To compare seed predation and germination between pasture and forests, five seeds were offered at 5, 10 and 15m from another 15 individuals marked at each habitat. Habitat alteration affected seed shadows and the dispersal distance was longer at the open vegetation of pasturelands (11.35 m forest vs. 14.21 m pasture). Seed predation was significantly higher in forests (59.05%) than in pastures (9.52%), but mortality by other factors showed the reversed pattern (22.3% vs, 90.2%). Temporal patterns of seed predation, mortality by other factors and germination also differed between habitats. Seed predation started late in pastures, probably because grass growth with the first rains provides foraging protection for predators from their natural enemies. On the other hand, seed mortality by other factors increased drastically in the same period, making most seeds produced in pastures unavailable for ground predators. As a whole, all seeds offered in pasturelands died after four months of experiment, whereas 16.1% of seeds were saplings in forest at the same date. Given the high rates of deforestation of Brazilian tropical dry forests, the absence of recruitment in pasturelands is a serious threat to the viability of C. arborea populations