The implications of harvesting on the population structure and sediment characteristics of the mangroves at Mngazana Estuary, Eastern Cape, South Africa

摘要

The Mngazana Estuary has the third largest area of mangroves in South Africa (118 ha) and one of the main environmental threats is the cumulative effects of long term small scale harvesting from local communities. This study investigated the change in aerial cover of the mangrove forest over time and assessed the effect of harvesting on the microenvironment and the population structure of Rhizophora mucronata (preferred harvested species) in both harvested and non-harvested sites. In 1982 there were 150 ha of mangroves of all species and since then 32 ha (21%) of the forest area has been lost. Areas of the estuary where mangroves have been completely removed showed significant differences in sediment characteristics. Changes in population size, ratios of adult trees to juveniles (harvested sites—1:5.5, non-harvested sites 1:3.4) and significant differences in height structure are some of the indications that harvesting is affecting the mangrove populations. Results show that while it is necessary to suggest proposals aimed at the sustainable use of the Mngazana mangroves, it is equally important in the short-term to make available alternative sources of materials to replace mangrove poles for building. The formation of the Mngazana Mangrove Management Forum provides an ideal opportunity to drive Participatory Forest Management (PFM) but this would require scientific and management support. The data shown here will provide ecological information required for PFM. Keywords Harvesting - Population structure - Management - Rhizophora mucronata - South Africa