Site conditions and growth of pines at the North East Cape Forests

Abstract

This study deals with a unique reconstruction of pine growth on various sites of the North East Cape Forests (NECF), thus providing information of strategic importance to the regional afforestation. The reconstruction of growth was possible in a number of plantations established by the former land owners in areas perceived to be marginal for industrial tree planting. In total, 21 survey sites were demarcated in stands of Pinus elliottii (14 sites), P. patula (6 sites) and P. radiata (I site). This study involved (i) determination of tree dimensions and tree condition, (ii) collection of dendrochronological information through stem analysis, (iii) detailed surveys of soils and other site characteristics, (iv) monthly measurements of soil water status at some of the sites, (v) data analysis with the major objectives to define the current yield, mean annual increment (MAI), and timber yield and MAI at harvesting age of 18 years, (vi) modelling of the growth-site relationships to predict site index (SI ₁₈) and MAI₁₈ with site characteristics.

The data showed that pines can produce over 20 m³/ha/a at the NECF if the site species matching is correct. However, stem quality of P. radiata and P. patula was poor. It is assumed that the frequent stem malformations resulted from (i) mechanical damage to the growing tips (hail), or (ii) physiological stresses induced during prolonged spring droughts. The preliminary results of the growth-site relationships showed that the knowledge of soil water storage, rainfall as well as air temperature, soil bulk density and carbon content of the soils was important to understand and predict growth of trees.