Site Productivity Assessment in Rainforests: An Objective Approach Using Indicator Species

Site productivity assessment is a prerequisite for growth prediction and yield forecasting. Site index (top height at an index age) is not suitable in rain forests where tree height is difficult to measure and tree age is impossible to determine. This paper reports a study which ranked 80 permanent plots according to potential diameter increment, and established equations which allow site productivity to be determined from the presence or absence of several tree species or from geological maps and Landsat TM data. Eighteen pandemic species were selected as a basis for comparing the growth potential of each plot. Regression analysis of their individual diameter increments was used to establish the plot's growth potential. This approach ensures freedom from biases introduced by species composition and stocking. The values determined by regression were scaled for convenience, into the range 3-10. Stepwise linear regression was then used to derive equations which would enable objective assessment of the productive potential of these and other rain forest sites within the region. Validation using independent data indicated that three equations, employing species occurrence, geology and Landsat TM data, provided reliable estimates of the productive potential of rain forest