Ecologia de epífitas vasculares nas florestas nebulares do Parque Estadual do Ibitipoca, Minas Gerais, Brasil

Abstract

The montane vegetation harbors great plant diversity due to the combination of features like the isolation, geodiversity and climatic variation in short distances, caused by elevation, which alter the plant community along the gradient. Epiphytes are especially rich in cloud forests of the Neotropical Region, but in Brazil there are only few studies in such vegetation. The Parque Estadual do Ibitipoca (PEIB), located at Serra da Mantiqueira, has a relief characterized by hills and cliffs, in altitudes between 1000 and around 1800 m that presents, interspersed to field vegetation, fragments of cloud forest and dwarfforest, being the latter divided in four physiognomies. These forest formations stand out for retaining moisture from the fog allowing high abundance of epiphytic individuals. In order to know the composition and structure of the community of vascular epiphytes in such formations were used specimens collected in the Park along more than 40 years deposited in herbaria, besides new expeditions conducted between July 2014 and July 2015 for observation, photographic record, and collection of the plants, which were deposited in the herbarium CESJ of Universidade Federal de Juiz de Fora. Results are presented in two chapters. The first chapter presents the checklist of vascular epiphytes in the cloud forests of PEIB, composed by 223 species distributed in 81 genera, being Pleurothallis s.l. R.Br. the richest (13 spp.), and 22 families, of which Orchidaceae is the richest (86 spp.), corresponding to 28% of the vascular flora of this formation. Both the absolute number of species and the epiphytic quotient represent one of the largest diversities ever found in such studies in the Brazilian Atlantic Forest, which is of great relevance if taking in account that the studied physiognomy represents less than 300 ha or around 20% of the total area of PEIB (around 1488 ha). This relevance is reinforced by the presence of 13 and 23 species threatened with extinction respectively in national and state levels in distinct categories. The second chapter presents the results of evaluation of the community of vascular epiphytes along the elevation and environmental gradients, represented by three of four subphysiognomies of dwar-forest. For this purpose were established 24 plots of 10 x 20 m, divided in eight sets each composed by riverine dwarf-forest with humiferous shallow soil, slope dwarf-forest with sandy deep soil, and slope dwarf-forest with sandy shallow soil. The establishment of the sets was based on the caves whose surrounding vegetation comprises the first aforementioned formation at different altitudes (Ponte de Pedra, Coelhos, Bromélias, Monjolinho, Cruzeiro, Pião, Viajantes e Três Arcos), being the other formations nearest as possible and with the most similar elevation possible. All phorophytes with diameter at breast height larger than 10 cm were analyzed in each plot. In order to evaluate the influence of luminosity on the ix occurrence of epiphytes, photographs of the canopy were taken, to estimate the cover percentage using the software CanopyDigi. The community structure was analyzed through calculation of absolute and relative frequencies, diversity index of Shannon (H’), uniformity index of Pielou (J), and taxonomic diversity indices [average taxonomic distinctness (K+) and variation in taxonomic distinctness (M+)], for each subdivision of the dwarf-forest and for the community as a whole. It were sampled 568 phorophytes (the richest having 29 species), resulting in 3771 occurrences of epiphytes, distributed in 146 species, of which 20 were accidental. Orchidaceae is the richest of the 22 families found, with 53 species (36%) and, together with Polypodiaceae (19 spp.), and Bromeliaceae (16 spp.), have 60% of the total. There was no correlation between the canopy cover and the observed richness of epiphytes (r = 0.26, p = 0.23). The values of H’ and J for the community were respectively 3.97 and 0.82. The diversity was different between the physiognomies of dwarf-forest and along the elevation gradient, being greater with enhancement of the elevation. The value of K+ to Gruta dos Coelhos was lower than expected, and represents a potential impact caused by the massive visitation of tourists, resulting in collection of ornamental plants or environmental degradation, once this is the cave of easiest access in PEIB. The obtained results highlight the diversity of this region and the important contribution of the epiphytes, as well as its sensibility to the different vegetation physiognomies and the climatic variations caused by the elevation, which conducted to an atypical diversity gradient, besides the importance of taking in account the anthropic impact, even in a conservation unity.