Effect of weeding and fertilisation on bark thickness and stem form of seven pine species on a low-elevation site at Usutu, Swaziland

Abstract

On a low-elevation site at Usutu alternative species to Pinus elliottii, the species recommended in the past for such sites, were planted to evaluate growth differences. At rotation age, destructive stem profile analyses were conducted on some of the trees in order to fit a taper equation with mixed effects linear modelling to the data, as very little information is currently available for these alternative species. The effects of the combined application of phosphorus and potassium  fertiliser and intensive weeding on stem form were also investigated. The application of fertiliser and weeding affected the stem form of some species in the trial. The results were, however, not consistent across all seven species. These results highlight the importance of developing accurate volume estimation models for each of the species, and preferably to have separate models for unfertilised and fertilised trees  as volume errors, ranging from an overestimation of 4% to an underestimation of 10%, might occur if the changes in stem form as a result of fertilisation and weeding are not taken into account.

Keywords: forest mensuration, Pinus caribaea, P. elliottii, P. kesiya, P. oocarpa, P. patula, P. tecunumanii, P. taeda, plantation, relative bark thickness, taper equation

Southern Forests 2009, 71(3): 215–225