An assessment of factors affecting early survival and growth of Pinus patula and Pinus elliottii in the summer rainfall region of southern Africa

Abstract

High initial mortality of pine seedlings planted in commercial timber plantations in the summer rainfall region of southern Africa has motivated research into possible causes. The objectives of this study were to assess whether survival and initial growth of Pinus patula and Pinus elliottii were related to site physiography, distribution of harvest residues and/or seedling size at planting. The study was carried out at three sites, situated in Mpumalanga, South Africa (1 trial), and Usutu, Swaziland (2 trials). Assessments of slope steepness, aspect, potential for water movement and harvest residue levels were made at three months after planting on 40-60 plots at each of the three trials. Survival, height and groundline diameter of the seedlings were also assessed at 1.5 months, 12 months, 18 months and 24 months after planting. Linear correlation, t-tests and analyses of variance were used to determine whether functional relationships existed between harvest residue levels, site physiography, seedling size, survival and growth. The outstanding results from this study were that neither site physiography nor harvest residues were found to be predictors of early survival, or growth, of P. patula and P. elliottii. The overall poor survival of P. patula in contrast to P. elliottii, despite similar exposure to stress inducing factors, highlighted the sensitivity of this species. One of the most interesting outcomes of this study was the indication of a positive relationship between initial seedling height and subsequent growth. While the results presented here cannot provide sound evidence for the strength of this relationship, the effect of seedling height (and more importantly size) at planting (and the causes there-of) and subsequent growth requires further investigation.

Keywords: physiography, harvest residues, seedling size

Southern African Forestry Journal No. 205 2005: 21-30