Relações florísticas e estruturais do componente arbustivo-arbóreo e regenerante no Parque Nacional da Furna Feia, RN

Abstract

The Caatinga is the main ecosystem located in a region with a semi-arid climate, being a great habitat for plant and animal species, landscape variety, high biological richness, and several endemic species. Composed of a xerophilous and heterogeneous vegetation in terms of phytophysiognomy and structure, with a predominance of small trees and shrubs, with small, deciduous leaves, equipped with adaptation mechanisms to the condition of water scarcity. The history of land occupation and exploitation in the Brazilian Northeast has caused strong anthropic pressure on these areas of Caatinga, causing significant losses of native vegetation, which is linked to an exploitation model characterized by the deforestation of native areas for livestock, extraction of wood for firewood, growing agricultural plants, hunting, building roads and highways, and misuse of fire. The present study was carried out in the Furna Feia National Park, in two sub-areas classified according to historical use: (A1) disturbed area, and (A2) preserved area. Twelve sampling units was carried in each subarea, composed of plots of 20.0m x 20.0m (400m²) randomly distributed, located with a GPS receiver and marked with a tape measure. In each plot, all live shrubs/trees with a circumference of 1.3 m from the ground (CAP) ≥ 6.0 cm were sampled and labeled, and the floristic sampling intensity was defined as a function of the population variance, until reaching the stability of the collector curve. For multistem individuals, the equivalent diameter was adopted. In the sampling of natural regeneration, a sub-plot was implanted in one of the ends of each plot, with 1.0 x 20.0 m (20m²), being sampled all shrub/tree individuals with a minimum height of 0.5 m, grouped in three height classes, where: C1 = Height (H) ≥ 0.5 to 1.5m; C2 = Height (H) > 1.5 to 2.5 m and C3 = Height (H) > 2.5 m. The floristic sufficiency of the adult component was obtained in the fourth plot at 1,600m², suggesting that the sample is sufficient for floristic representation of both subareas. In subarea A1, 933 individuals of 29 species and 15 botanical families were sampled, while in subarea A2, 1,137 individuals of 23 species and 14 botanical families were sampled. In both subareas, the Fabaceae family was the richest in number of species, followed by Euphorbiaceae, with the largest number of individuals, respectively. There is a low similarity in the number of individuals between the subareas, on the other hand there is a high similarity of species shared in the subareas. Floristic sufficiency of natural regeneration in subarea A1 was reached in the 9th plot at 180m², and in the 5th plot at 100m² for subarea A2, configuring that the sampling was sufficient to represent the floristic composition of the subareas. In general, Fabaceae was the family with the highest representation of species sampled in both subareas, responsible for the largest number of regenerating individuals, but most of the sampled species is in the initial class (C1). Of the 29 species sampled in the adult component, only 16 were found in the regenerating component. Of these, only 4 species presented individuals in the C3 classof the A1 subarea, and only 2 in the A2 subarea. Mimosa arenosa was the only species with regenerating individuals in the three height classes in both subareas, with the highest rates of total natural regeneration. Diversity showed a reduction as the height class increased, an inversely proportional behavior occurred with equability. There was a low sharing of regenerating species between subareas, this low similarity is understood as a reflection of past environmental events, such as disturbances suffered by sporadic human action in subarea A1, as well as prolonged droughts in periods prior to field collections.