Composition and size class structure of tree species in Ihang’ana forest reserve, Mufindi district, Tanzania

Abstract

Ihang’ana Forest Reserve is part of the Udzungwa Mountains ecosystem that falls under the Eastern Arc Mountains (EAM). Previous plant biodiversity studies in this ecosystem concentrated on large-sized Forest Reserves of greater than 20,000 ha (FR) such as the Uzungwa Scarp ignoring small-sized forests of less than 300 hectares. This study was therefore undertaken to assess tree species composition, structure and diversity in Ihang’ana FR (2982 ha), one of the forest reserves in the Udzungwa Mountains Ecosystem. A total of 7 transects with 12 plots of sizes 20 m x 50 m each were established for vegetation sampling. Seventy tree species representing 32 families and a total of 6478 individuals were identified from Ihang’ana FR.  Alpha diversity ranged between 1.334 and 2.865 (mean 2.246 ± 0.309) with most plots recording species diversity of greater than 2.014. The most frequent occurring species were Aphloia theiformis (96.4%), Diospyros whyteana (91.6%), Nuxia floribunda (91.6%) Olea europaea (86.9%) and Macaranga capensis var. capensis (77.4%). Majority of these species similarly scored the highest Importance Value Index (IVI) as follows: Aphloia theiformis (112.6), Nuxia floribunda (111.36), Olea europaea (101.75), Bridelia micrantha (101.25), Diospyros whyteana (98.06), Macaranga capensis var. capensis (87.62), Morella salicifolia (71.3). M. capensis var. capensis, an indicator species for disturbance, was poorly represented in the lower DBH size classes, possibly an indication of forest recovery from past disturbance. Despite reports that licensed timber extraction used to take place in the forest in the early 1980s, the situation on the ground as observed during this study shows that the forest has recovered from such disturbance. It is therefore recommended that the central government continue supporting the local communities around the forest reserve for example in maintaining fire lanes as part of conservation and management of Ihang’ana Forest Reserve