Análise da vegetação e estimativa de biomassa e carbono em uma área de caatinga no sertão do Rio Grande do Norte.

Abstract

Caatinga is a biome classified as tropical dry forest and comprises approximately 11% of the Brazilian territory. Its vegetation has a high endemism rate and it is greatly adaptable to the extreme climatic conditions on the Brazilian drylands. Approximately 29 million inhabitants live in the area where the Caatinga is predominant and due to centuries of unmanaged use of forest resources, it is now one of the most seriously endangered and least known biomes in the planet. Therefore, the objective of this work was to carry out an analysis of the tree-shrub vegetation and estimate both the biomass and the carbon of a caatinga area in the town of Caraúbas, located in the state of Rio Grande do Norte. For that purpose, 12 partitions, measuring 20 x 20 m (400 m2) each, were allocated adding up to 4800 m2 of total sampled area. All individuals with CBH > 6 cm were measured, a total of 1942 ind.ha-1. The distribution of the samples included 19 species, 17 genera and 9 families, most of them Fabaceae and Euphorbiaceae (9 and 3 species, respectively). After analyzing the floristic and phytosociological parameters, the species that obtained the highest values of ecological importance in the area were: Cordia glazioviana, Combretum leprosum, Cenostigma pyramidale, Mimosa ophthalmocentra and Mimosa tenuiflora. In order to explore their natural regeneration, subdivisions of 20 m2 were employed, allocated within the partitions that comprised the forest inventory, where 75 samples were distributed in 11 species, belonging to 5 botanical families, with special attention to the species Croton blanchetianus, Mimosa ophthalmocentra, Mimosa tenuiflora and Jatropha mollissima, with (21; 12; 11 and 9 samples, respectively), representing 70.66% of the evaluated regenerants. The Shannon diversity index (H') for the adult component was 1.83 nats.ind-1 and regeneration index was 2.04 nats.ind-1. The adult shrub/tree and the regenerating components have a floristic diversity at the same level of the local anthropized caatinga. The subdivisions allocated within the lots applied in the forest inventory were used for the evaluation of the biomass by the destructive method, measuring 10 x 10 m, and all individuals in their inner side were slayed and traced; the stem components such as thick branches, thin branches and leaves were weighed separately. Approximately 100g of samples from each compartment were collected and taken to the laboratory to determine the dry mass. Along with the calculated data, the mathematical models were adjusted contemplating the sum of the components of the arboreal-bush individuals. The total quantified biomass for the 5 evaluated species was approximately 11.05 t.ha-1 and fixed carbon was estimated at 5.52 t.ha-1. The evaluated mathematical models were Chapman-Richards’, Schumacher’s and Hall and Naslund’s classic equations, that presented satisfactory adjusted R2 indexes.