ASSESSMENT OF THE STRUCTURE AND BIOMASS ACCUMULATION IN MANGROVE FOREST OF KILIFI CREEK, KENYA

Abstract

Mangroves are typical marine ecosystems in tropical and sub-tropical coasts and are one of the most productive systems in the world. In Kenya, mangroves have formed well developed forests in sheltered coastlines such as bays, creeks and estuaries as well as in deltas. This study assessed quantitatively the structure and biomass accumulation of the mangrove vegetation of Kilifi Creek. The study also estimated the above and below ground biomass accumulation in Kilifi mangrove forest. Forest structure was analyzed using the quadrat method where belt transects were laid perpendicular to the shoreline at Kibokoni and Maya covering different vegetation types. A total of 152 quadrants were laid along 10 transects at Kibokoni and 145 quadrants along 9 transects at Maya. The stand density varied between 1,488 trees ha–1 and 1,849 trees ha–1 between the two sites representing Kilifi creek. Six of the nine mangrove species found in Kenya were observed in Kilifi. These included; Avicennia marina (Forsk.) Vierh. (Acanthaceae), Bruguiera gymnorrhiza (L.) Lam., Ceriops tagal (perr.) C. B. Rob., Rhizophora mucronata Lam. (Rhizophoraceae), Sonneratia alba Sm. and Xylocarpus granatum J. Konig. Based on species importance value (I.V), the dominant mangrove species were R. mucronata and A. marina which is typical of mangrove forests in Kenya. The allometric equation which uses stem diameter and specific wood density as predictive variables with high coefficient of determination (r2) of 0.979 and 0.954 respectively was used in estimating the above and below ground biomass accumulation. In comparison of the four dominant mangroves species, R. mucronata had the highest tree biomass accumulation of 85.7 + 16.3 Mg ha-1. This was followed by A. marina with 69.6 + 12.1 Mg ha-1. Sonneratia alba had 65.6 + 12.3 Mg ha-1 while C. tagal reported a value of 53.5 + 16.4 Mg ha-1. There were significant differences in above ground and below ground biomass accumulation across the two sites with (F (1, 4) = 5.21, ρ < 0.05) and (F (1, 4) = 7.25, ρ < 0.05) respectively. Total biomass accumulation was similarly significantly different across the two sites (F (1, 4) = 5.12, ρ < 0.05). A root: shoot biomass accumulation ratio of 1:2.7 was calculated for the whole of Kilifi creek mangrove forest. The findings of this study show the structural vegetation composition and estimates of tree mangrove biomass which can be utilized for conservation through negotiation of carbon credits in the carbon market and will aid in developing management strategies.