Inventory time-cost and statistical power: a case study of a Lao rattan

A pilot study was conducted to determine the optimal survey design for an i nventory of the commercially important rattan Calamus poilanei in central L ao PDR. Simulations were used to estimate the coefficients of variation (CV s) of population density estimates for alternative sampling designs, a mode l was developed to determine the optimal survey design which minimised surv ey time for a given survey precision and a statistical power analysis was u sed to determine whether these surveys were sufficiently sensitive to form part of a monitoring programme. Line survey and plot enumeration times were quite high due to moderately di fficult terrain. The Cv (135% for a 5 m x 50 m plot) was markedly higher th an in some comparable studies. The CV could be predicted well from plot siz e but plot shape explained little additional variance. The optimum plot siz e varied but the 5 rn x 50 in plot was close to the optimal solution over a wide range of situations. Surveys with a precision of 20% or better were p redicted to be very time consuming. Power analysis indicated that a survey precision of 5 or 10% was likely to be required if an annual monitoring pro gramme was to be useful in detecting a decline in the population. To achiev e this precision, surveys would have to be even more time consuming, and ma ny 'optimal' solutions were clearly impractical. For a resource of moderate value such as rattan cane, very prolonged or costly surveys such as these are most unlikely to be economically justified. (C) 2001 Elsevier Science B .V. All rights reserved.