Evaluation of mangrove structure and condition in two trans-boundary areas in the Western Indian Ocean

Abstract

1. The structure, forest condition and regeneration status of nine mangrove forests in two trans-boundary areas of Mozambique bordering Tanzania and South Africa were studied. The main objective was to estimate the cutting intensity in the selected sites – Saco and Sangala in southern Mozambique; Mecu´ fi, Pemba, Ibo, Luchete, Ulo in northern Mozambique, and Mngoji 1 and Mngoji 2 in Tanzania. 2. A total of 135, 10m 10m quadrats were set in the outer, middle and lower parts of the mangrove forests at all sampling sites. Measurements included stem diameter at breast height (DBH) and height of adult trees (i.e. all trees with stem diameter more than 2.5cm). Young trees (with stem diameter of less than 2.5cm) were classified as juveniles. To assess forest condition, trees within the quadrat were classified into intact, partially cut, coppiced, die back and stump. Pole quality was appraised through the classification of the lead stem into three categories–straight, semi-straight and crooked poles. 3. The results indicate different levels of exploitation with Mngoji 1 and Mngoji 2, the most degraded sites, having stump densities of 959stumpsha1 and 592stumpsha1, respectively. Most sites had mostly poles of inferior quality (crooked poles), but high densities of straight and semi-straight poles were found in Mngoji 1 (742stemsha1) and Saco (636stemsha1). 4. Natural regeneration was observed in most sites but not for all species, with adequate regeneration in Saco (14766 saplings ha1) and Mecu´ fi (14706 saplings ha1), while low regeneration was recorded in Mngoji 1 and 2 (2212 saplings ha1 and 4799saplingsha1, respectively). 5. These results indicate the need for improved mangrove management and replanting especially in mangrove depleted conservation areas of southern Tanzania.