Growth rings and stem diameter of Dichrostachys cinerea and Senegalia mellifera along a rainfall gradient in Namibia

Abstract

Tree ring studies, have been an important tool for studying climate variations since the beginning of 1900s due to their ability to preserve of information about abiotic and biotic factors. This study is aimed at understanding the growth rings of two aggressive encroachers in Namibia, Dichrostachys cinerea and Senegalia mellifera. We used three sites across a rainfall gradient from 250 to 600 mm/yr, where the stem discs were collected and processed from all species. Stem discs of different sizes of the two species were sampled from each site, air dried, polished and characteristics of growth rings were analysed using WinDENDRO, COFECHA and SPSS software. Growth rings were present for both species across all three sites, however the characteristics of the rings varied by site. Both species show a positive relationship between stem diameter and heartwood diameter and also between numbers of growth rings and stem diameter. Stem diameter did not necessarily relate to the age of the tree. It is concluded see that growth ring characteristics of the two species vary by geographical location and are influenced by complex environmental interactions, mostly rainfall.