Afforestation site assessment : a study of indirect productivity evaluation procedures

Abstract

A comprehensive review of the forestry literature on site assessment was undertaken to determine and critically evaluate the theory and methodology of existing procedures for indirect productivity evaluation applicable to afforestation in New Zealand. This review identified two traditional approaches to indirect productivity evaluation for afforestation: the factorial approach, involving the generation of predictor equations, and the holistic approach, involving site classification and ordination. The literature review also suggested that these two approaches are not mutually exclusive but can be effectively integrated in a three stage research strategy designed to produce quantitative gradient models of forest ecosystems. The first stage in this research sequence generates a multiple linear regression model of the relationship between tree crop growth rate and selected quantitative abiotic environmental parameters. The second stage involves analysis of the residuals from the multiple linear regression model to determine the cause of unexplained variation in tree crop growth rate. The results of these two analyses provide the information required to construct a graphic co-ordinate system with axes corresponding to continuous gradients of the selected quantitative abiotic environmental parameters. The final stage of the research sequence is gradient analysis within the framework of the quantitative abiotic environmental coordinate field to delimit site-types, each relatively homogeneous and distinctive in the abiotic structural components of the forest ecosystem it encompasses. A field study was carried out to examine the effectiveness of this research strategy under conditions of actual use for afforestation with Slash Pine in the Auckland Forest Conservancy. The results of this field study indicate that the research strategy of the integrated approach provides methods for objective site classification and potential productivity evaluation which can be applied not only to afforestation areas but to any type of terrestrial ecosystem for the purposes of renewable natural resource management.