Estudos fitossociológicos e dendrométricos em um fragmento de caatinga, São José de Espinharas - PB.

Abstract

The present work aims to analyze the floristic composition, characterize the parameters of the horizontal, vertical, internal, parametric and regeneration structures, adjust volumetric models in order to obtain stem volume estimates as well as estimate a form factor for stems in caatinga vegetation. The study area is located in the Cachoeira Settlement, in the municipality of São José de Espinharas-PB. We used 49 sample with an area of 400 m² (20 x 20 m), systematically distributed, spacing between plots of 300 x 300m, demarcated with the help of GPS navigation (Global Positioning System). To collect the inventory data, regeneration and the internal structure (Class of vitality, quality of stem, crown position and height of bifurcation), the Measurement Network Management of the Caatinga Protocol was followed. For the study of volumetric estimates, we used a 225 sample stem. For each stem, measurements of the circumference at 0.30 m above the ground (C0, 30), circumference at breast height (CAP) and total height of the largest stem were taken. In the rigorous scaling procedure, the stem was measured in sections (1 m), by the method of Smalian, up to a minimum usable value of about 1.5 cm diameter, taking notes, where appropriate, of the circumference and length fraction of the final section. After the measurements, the total volumes per stem were obtained. We used Schumacher and Hall (1933) models, Spurr model in the linear form, and the model in the Schumacher and Hall (1933), in the non-linear form, all of them with two options for the independent variable, diameter at 0.3 meters above the ground and equivalent diameter, totalizing six models. The form factor was estimated by the ratio between the actual volume obtained by stem rigorous scaling and cylindrical volume, whose base is the sectional area obtained by the DAP at 1.30 m and height of the stem. The tabulation, processing and analysis were carried out using the software Microsoft Office Excel 2007, Statistica and Mata Nativa 2.0. We found, in the study area, 30 species and 15 families and 26 genera. The species Luetzelburgia bahiensis, listed in this work, is not present in previous records. There is no record about its occurrence in the vegetation of Paraiba. The species with the highest density were: Croton blanchetianus, Poincianella pyramidalis, Mimosa tenuiflora, Combretum sp, Aspidosperma pyrifolium and Mimosa ophthalmocentra. The species with the largest VI (%) in the area is P. pyramidalis with 23,46 %. On the vertical structure, the second height class presented a greater steam distribution in density in the study area. In regeneration, the species C. blanchetianus, Combretum sp. and P. pyramidalis showed a higher steam density in the area. The first three diametric classes have the largest number of stems of the forest. Class I 60 1%, Class II 28,25% and Class III 8,17%, totalizing 96,53%. Over 71% of the stems in the caatinga were healthy. The obtained value was 0.87 for the studied form factor. The first four volumetric models showed good performance for volume estimates of stems in the caatinga.