Effects of traditional harvesting techniques on the growing stock of Rhizophora mucronata and Ceriops tagal in Lamu Mangrove forest, Kenya
Bisia, David Kodia
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The gazetted forest area in Lamu District is 50093.4 ha of which mangroves occupy 46,184 ha. and 85% of mangroves in Kenya. The Bajuni in Lamu depend on mangrove harvesting and fishing as their main source of income. They use traditional techniques when harvesting the mangroves since Forest Department does not have alternative harvesting methods. The Forest Department carried out inventories in 1967 and 1981 that assessed the then existing mangrove-growing stock. The inventories revealed that Rhizophora mucronata and Ceriops tagal the most preferred species in the Southern Mangrove Swamps had been depleted. The Government placed a ban on mangrove harvesting for charcoal production in 1972 and poles for export in 1983. The Southern Mangrove Swamps were closed to harvesting. However, the harvesting of poles for the local market was allowed in the Northern Mangrove Swamps. There have been subsequent prohibitions on mangrove harvesting for local market by the Government. There have been outcries from the mangroves dependant community over these prohibitions. The community believes that its harvesting techniques do not deplete the growing stock. The purpose of this study was therefore to determine the effects of traditional harvesting techniques on the growing stock of the mangroves in Lamu. The study assessed combined carrying capacities of regeneration potential, established regeneration and the growing stock for Rhizophora mucronata and Ceriops tagal in the previously harvested and un-harvested sites before the closure of Southern Mangrove Swamps in 1983. It also assessed the activities undertaken during harvesting through demonstration by one of the mangrove cutters; how harvesting techniques are acquired and effects of the harvesting prohibitions on the mangrove dependent community was investigated through a semi-structured interview. The study was carried out at Mokowe, Kizuke and Funga Mbuzi in the Southern Mangrove Swamps. The data on regeneration potential, established regeneration and growing stock were analyzed using sample means. A two-sample t significance test was used in finding out if there are any significance differences in regeneration potential and growing stock between harvested sites and those that had not been harvested at Kizuke and Funga Mbuzi. Sample means in the closed canopies at Mokowe, Kizuke and Funga Mbuzi for regeneration potential, established regeneration and the growing stock were compared. The results indicated that there were significances differences in regeneration potential and the growing stock between harvested and un-harvested sites. Harvested sites had higher regeneration potential and growing stock than un-harvested sites. At Mokowe, where we had maximum forest policing, carrying capacity for regeneration potential was lower that at Kizuke and Funga Mbuzi. It was observed that harvesting techniques are non destructive. From the semi-structured interview, harvesting techniques are passed from generation to generation through family lines and that Lamu mangrove dependant community main source of income is mangrove trade. Any prohibition on mangrove harvesting has negative impact on their livelihood. It is therefore recommended that selective harvesting of mangrove poles using traditional harvesting techniques should be allowed given that it enhances regeneration potential and subsequently the growing stock. This would also alleviate poverty to mangrove dependant communities at the Kenyan Coast. Traditional harvesting techniques should be enriched with the scientific knowledge to develop mangrove management plans for Kenyan mangroves. Commercially exploitable forests should be managed for suitable yield while adequate protection should be accorded to depleted portions of the forest. Poorly stocked areas especially where there are a few or no mother trees, should be protected until they regenerate and replanting should be carried out in completely depleted sites.