Ecologia de epífitas vasculares em áreas verdes urbanas na Zona da Mata, Minas Gerais, Brasil

Abstract

Urbanization is a growing and ever-changing process and the urban green areas represent a shelter for nature. Epiphytes are plants that grow upon other plants without parasitizing them, that is, without removing any nutrients from them, and their presence in urban areas, despite the lack of studies, helps in assessing the environmental quality of the city and its surroundings. The aims of the study were to characterize the composition, structure and floristic diversity of the vascular epiphytic component in 26 urban green areas of 14 municipalities, located in the Juiz de Fora Microregion, Zona da Mata of Minas Gerais State; to investigate the floristic similarity between the areas and to evaluate the importance of environmental variables on this composition. The following hypotheses were tested: 1) the community of epiphytes will present low richness and diversity of species due to the susceptibility of this synusia to anthropogenic disturbances; 2) there will be low beta diversity due to the homogenization of the flora of the urban environment, which tends to present a reduced set of species that are more tolerant to such disturbances. In order to evaluate the community were calculated the relative and absolute frequencies, Shannon diversity index (H’) (compared through the Hutcheson t test) and Pielou equability (J'). A cluster analysis through UPGMA using Jaccard index was performed to evaluate the floristic similarity, and the relationship between the floristic composition and environmental variables were evaluated through a canonical correspondence analysis (CCA). A total of 110 epiphyte species were sampled in 26 green areas. Two Bromeliaceae species have the highest absolute frequencies: Tillandsia recurvata (L.) L. (68,8%) and T. tricholepis Baker (65.3%), together accounting for a relative frequency of 48,8%. Other four species worth mentioning due to the high frequency: the Polypodiaceae Microgramma squamulosa (30,8%), Pleopeltis astrolepis (19,4%) and P. pleopeltifolia (14,1%), and Rhipsalis lindbergiana (Cactaceae) (13,6%). The remaining species occurred in less than 10% of the sampled phorophytes. The H’ index value for the 26 areas was 2.44, and J' was 0.58, showing the dominance of the aforementioned species. In general, the MJF green area pairs presented Jaccard similarity index values higher than 25%, which is sufficient to consider the similar floristic composition between the areas. The CCA showed as important the following variables: average cloud cover, annual temperature variation, average annual temperature, evapotranspiration seasonality and elevation. It is possible to notice the homogeneity of the MJF epiphytic flora, probably due to the selection of tolerant species to the anthropic disturbance in the urban environment. Some results suggest that is necessary more comprehensive studies about the epiphytes in urban environment, like Orchidaceae as the richest family (once generally is poor in the such environment), better definition of the patterns of species distribution both regarding the anthropized environments and the relationships with exotic or native phorophytes, as well as to enhance the knowledge of the ecological functions played by the epiphytes in these places.