Levantamento florístico e fitossociológico de um remanescente de caatinga no município de Palmeira dos Índios, Alagoas, Brasil

Abstract

ABSTRACT

Caatinga is an exclusively Brazilian biome, predominant in the Northeast region, highly threatened and susceptible to degradation processes. With the unbridled use of the Caatinga, extensive areas have been discovered where the vegetation has lost its characteristic plant diversity. Once closed, activities such as extensive grazing and suppression will allow the medium or long term, the vegetation to regenerate. Thus, this study aimed to perform floristic and phytosociological survey of a remnant of caatinga in the municipality of Palmeira dos Índios, Alagoas, Brazil. The survey of the arboreal-shrub components of the Caatinga was carried out by means of simple random sampling in 35 plots with dimensions of 20 m x 100 m each, totaling 70,000 m2 of sampling area. In each plot, all arboreal-shrub individuals with circumference at breast height (CAP) were quantified ≥ 6 cm and measured at height and diameter. The collected material was identified with the aid of specific bibliography and by comparison with the material of the collection present in the herbarium of the Institute of Environment of Alagoas - IMA/AL following the APG IV system. The dispersal syndromes were classified into three categories: anemochoric (dispersed by wind), zoochoric (dispersed by the animals) and autochoric (they present self-dispersion, by gravity and those with explosive dispersion). For the analysis of floristics, the Euclidean distance was used as a similarity function, because it is the most used in cluster analyses and presented greater ease of calculation. For phytosociology, parameters such as density (AD), relative density (DR), dominance (DOA), relative dominance (PAIN), frequency (AF), relative frequency (RR) and importance value (VI) were calculated. It is observed that the area has a total density of 17.76 ind ha-1 of 2.58 m2 ha-1 basal area (AB). The Shannon-Weaver diversity index (H'), was 1.90 nats per ind, which indicates low diversity, the same behavior occurred with the Simpson dominance index (C), where the observed value was 0.21. Regarding the distribution of individuals by diameter class, most were positioned in the first diametric classes, decreasing numerically, that is, when the diameter increases the number of individuals reduces. The families Fabaceae (Leguminosae) and Euphorbiaceae stood out for presenting the largest number of shrub-tree species in the study area. The studied area is still in the initial stage of ecological succession evidenced by the low floristic richness and the higher occurrence of species of the genus Croton that are pioneers of secondary forest areas. The woody vegetation of the study area is open and its phytophysiognomy is characterized as arboreal caatinga, which indicates that the vegetation is still in the process of succession. The results showed the predominance of Autocooria dispersal syndrome, which is the most frequent in the tree habit. Keywords: Structure, Diversity. Ecological succession.