Avaliação do tamanho de parcelas e intensidades de amostragem para a estimativa de estoque e estrutura horizontal em um fragmento de floresta ombrófila mista

Abstract

The use of sampling techniques in forest inventories generates information regarding natural resources, contributing to the decision making of managers in the public and private spheres. Considering the importance of information generated by the use of sampling techniques, the objective of this study was to assess the influence of different plot sizes and sampling intensities to estimate the stock and phytosociological parameters. The studied area corresponds to a Mixed Ombrophylous Forest remnant, of 15.2 ha, located in the Campus III – Jardim Botânico, which belongs to the Federal University of Paraná. The methodological approach of this study consisted initially of the georeferencing of the study area and a census, of all trees with breast height diameter (DBH) greater than 10 cm. The collected data were included in a geodatabase. After this step 20 sampling variations of fixed area were defined to perform the inventory simulations. This process considered the combination of different plot sizes (200sq.m, 400sq.m, 500sq.m and 1000sq.m) with different sampling intensities (2%, 5%, 10% and 15%). The results indicated that the area contains 121 tree species, distributed in 47 families and 80 genera. In terms of species diversity the predominant family is Myrtaceae. The average forest basal area is 22.05sq.m/ha and the average number of trees is 601N/ha. The comparison of the census results with those obtained through the sampling simulations indicated that the sampling technique is quite reliable when the forest is considered as a whole. However, when the results are evaluated at the species level, they show a strong deviation in relation to the parametric value. In general an increase in sampling intensity provided an improvement of the estimations at species level. However it was observed that for plots of 200sq.m the variable of interest presented a highest value. The opposite was observed in larger plots. Plots of 1000sq.m tend to capture more accurately the variation of the spatial distribution of the variable of interest. Thus the obtained results are more reliable than those from 200sq.m plots with the same sampling intensity. In addition, plots of 1000sq.m were more precise for the estimation of the species cover index. The results corroborate with the hypothesis that to estimate the stock of a forest and phytosociological indexes larger plots present a better performance, particularly for species of great representativity in the forest. The only situation in which smaller plots might perform better is to estimate indexes related to rare species (less than one individual per hectare). Based on this it is recommended that for estimations regarding stock and phytosociological indexes, plots of at least 1000sq.m should be used and a sampling intensity as high as time and financial resources allow. Keywords: Forest inventory, sampling method, precision, phytosociology, spatial distribution, diametric distribution.