Forest structure and biomass of mangroves in the Mgeni estuary, South Africa

Abstract

Forest structure and biomass were determined in a mangrove stand dominated by Bruguiera gymnorrhiza (L.) Lam. Trees in 5 m² sample plots were harvested at ground level and then further cut into 1 m strata for separation into living wood, dead wood, leaves, reproductive material and pneumatophores. Mean above-ground living biomass was calculated at 94.49±7.83 t dry matter ha⁻¹, while dead wood contributed a mean mass of 7.63±0.89 t dry matter ha⁻¹. Excavations of roots yielded a below-ground biomass of 9.67 t dry matter ha⁻¹ which represented only 9.8% of the above-ground value. There was a mean density of 4700 living stems ha⁻¹ with plant heights ranging from 0.57 m to 5.80 m. Mean LAI was 4.95±0.80. As a basis for estimating standing biomass, regression lines were fitted to biomass values from individual trees of B. gymnorrhiza and Avicennia marina (Forssk.) Vierh. of various sizes. A comparison of these relationships with methods used by previous workers for estimating biomass suggests that most other methods cannot be applied without modification for local stands of mangroves.