O papel da diversidade das espécies de plantas residentes no estabelecimento de Dicranopteris flexuosa (Schrad.) Underw nas veredas do cerrado

Abstract

Dicranopteris flexuosa (Schrad.) Underw is a weed included in a list of fern species most problematic to the environment, due to their potential to invade new environments (ie, their invasiveness), to replace native species in natural habitats (causing local species extinction) among other negative impacts on the environment, the use of resources or human health. These potentially invasive ferns exploit opportunities through deliberate or accidental transportation to a region where they have no natural competitors, herbivores or pathogens that would limit their occurrence. Due to its characteristics, in recent years D. flexuosa has replaced the native species of the ‘veredas’ of a protected area, National Park of Chapada dos Guimarães. Considering the importance of preserving this phytophysiognomy we investigate the role of diversity provided by native plant species in the establishment of D. flexuosa. Our hypothesis is that D. flexuosa will occur less frequently, occupying less vegetation cover in places with greater diversity of native plant species. In addition, we hope to identify the native species that contribute most to the protection of the assembly against the weed specie. We installed 33 plots of 1 m x 1 m in which we quantify richness and cover occupied by each plant species (ranging from 0 to 100%). To estimate the biomass of D. flexuosa, we divided the plot into 4 parts (50 x 50 cm) and collected the biomass in one part at ground level. We found that richness of species of resident plants is not correlated with the cover and biomass of D. flexuosa. The biomass of weed specie was also not affected by the diversity of plant species. However, the area occupied by D. flexuosa was significantly affected by diversity of resident plant species. When the weed specie was absent, 18 new plant species occurred, all of them with herbaceous life habits. Another 13 plant species were able to coexist with D. flexuosa. Of these, 6 species occurred both in plots with the presence of D. flexuosa and in plots where it was absent. But the other 7 plant species, all with a tree-shrub habit, occurred only in the presence of the weed specie. The specie that showed strongest negative correlation with D. flexuosa was Aristida sp., native grass more abundant in ‘veredas’. Our results suggest that species diverisity of resident plants strongly reduces the success of establishing D. flexuosa. Plant species can present different degrees of contribution to ecosystem invasiveness. Aristida sp. seems to play a significant role in relation to other native species in the control of D. flexuosa cover because of the niche similarity, which limits the co-occurrence of both by competition. Resource sharing and positive interactions between species of herbaceous habit contribute to reduce invasiveness of assembly. Native species of tree-shrub habit can co-occur with weed specie by niche differentiation. We conclude that the maintenance of local biodiversity is an important mechanism to prevent the arrival and establishment of non-native species with potential to reducing local density of native species.