O papel da vegetação residente no estabelecimento de plântulas com diferentes características funcionais

Abstract

Root competition is considered an important process in forests with nutrient-poor soils. Species with different functional traits may have distinct responses to root competition along an environmental gradient. The main objective of this study was to investigate how three plant species with different functional traits respond to root competition with the neighboring vegetation along an environmental gradient in secondary forests. A second objective was to investigate if the resident understorey vegetation cover reduces seedlings consumption by herbivores, ameliorating the negative effects of root competition. The study was conducted in six secondary forests with distinct ages in Central Amazonia. At each forest, five blocks were established for a total of 30 blocks in the experiment. Each block included a pair of plots: control and treatment. The treatment plot was trenched and the understorey vegetation was removed. In each plot two individuals each of Bertholletia excelsa, Hevea brasiliensis and Handroanthus serratifolius were planted, totaling 120 individuals per species. The seedlings were monitored every three months and causes of death were registered whenever possible. After 10 months of records, for each species, competition indexes, site suitability indexes and biotic disturbances intensity were calculated based on final biomass and seedling monitoring. Functional traits of all live seedlings, canopy openness above the plots and available nutrients in the soil were also measured. For all species, the indexes of competition varied from positive (facilitation) to negative (competition) and the importance of root competition was associated with species-specific site suitability indexes. Root competition affected functional traits by reducing the light capture efficiency for all species. Biotic disturbances explained most of the variation among the species-specific site suitability indexes for seedlings of B. excelsa and H. brasiliensis. The availability of resources seems to play a secondary role for all species. The intensity of biotic disturbances was not negatively associated with understorey vegetation cover. These results highlight that root competition is more important in sites where seedlings become more developed. Facilitation occurred at the most severe level of the environmental gradient and may be related to reduced biotic damage in plants in control plots when damage is high for seedlings of B. excelsa and H. brasiliensis. Individuals of each species were consumed by distinct herbivores and the attractiveness of the understorey vegetation for different herbivores may have influenced more than the vegetation cover when facilitation occurred.