adasd

IPEF, n.38, p.17-22, abr.1988

A AMOSTRAGEM ÓTIMA EM INVENTÁRIO FLORESTAL
FREDERICO PIMENTEL GOMES
ESALQ/USP. Departamento de Matemática e Estatística
13400 - Piracicaba - SP
RAUL CHA VES
Duratex Florestal S.A.
13200 - Jundiaí - SP
ABSTRACT - This paper discusses the determination of optimum plot size in forest inventory, using two-stage sampling and taking in account the intra-class coefficient of correlation (ρ) among sub-plots within plots. The optimum plot size is defined as the size plot that, for a fixed cost, minimizes the variance of the sample mean. Data of two populations of E. grandis and two of E. saligna were analyzed, leading to average estimates ρ = 0.704 for E. grandis and ρ= 0.536 for E. saligna. These estimates were proved to be statistically different, at the 5% probability level. Application of the theory led to the recommendation of plots of 100 to 200 m2, when the relation of cost of access/cost of measuring sub-plots of 100 m2 is not greater than 4. The use of smaller plots, under the conditions of the populations studied, can reduce in about 55% the cost of sampling, without 1055 of precision, when plots of 100 m2 are taken, or else in about 45%, in the case of plots of 200 m2 (instead of 600 m2). Alternatively, if cost of sampling is kept constant, plots of 100 m2 (instead of 600 m2) lead to a decrease of about 33% in the standard error of the sample mean. The decrease is about 27% when plots of 200 m2 are used. Obviously, the reduction of the size of plot is always followed by an increase in the number of plots included in the sample, but the total area covered by the sample is decreased.
RESUMO - Este artigo discute a determinação do tamanho ótimo de parcelas para inventários florestais, através do uso de amostragem de duplo estágio e levando em conta o coeficiente de correlação intraclasse (ρ) entre subparcelas dentro de parcelas. Define-se como tamanho ótimo o tamanho da parcela que, para um custo fixo,