Assessment of African Blackwood (Dalbergia melanoxylon) Population Structure in Kilwa District, Tanzania

Abstract

Overharvesting and limited conservation efforts have posed a serious threat to future availability of Dalbergia melanoxylon in Tanzania in recent years. The study was conducted between 2018 and 2020 covering Mitarure Forest Reserve (MFR) and 2 surrounding community forests of Ngea and Nambawala in Kilwa District. The purpose of the study was to assess the existing population status of the species in Tanzania. A total of 36 circular plots in Mitarure and 15 plots in each community forest were laid down. Data were recorded for the number of stems per plot, and then converted on per hectare basis where the basal area and densities per hectare were calculated. Data was disaggregated into 5 Diameter at Breast Height (DBH) generated distribution classes ranging from DBH 0 to more than 45 cm. The results revealed that, there was a contrast between the Mitarure Forest Reserve and community forests in terms of individual number of trees per unit area, basal area and densities. The numbers of stems per hectare for the species were found to be 16, 10 and 8 stems/ha in Mitarure, Ngea and Nambawala forest, respectively. Dalbergia melanoxylon in Mitarure forest was normally distributed. The respective basal area was over 80 m² per ha in Nambawala against over 60 in MFR and Ngea. The results suggest success of the communities in conserving the species after previous overharvest. Authorities should frequently visit forests to increase the population of the species and reduce unauthorised harvesting.

Keywords: Dalbegia melanoxylon, Population structure, Mitarure forest reserve, Ngea and Nambawala community forests.