A method for monitoring mangrove harvesting at the Mngazana estuary, South Africa

The Mngazana estuary supports the third largest area of mangroves, and probably the largest stand of Rhizophora mucronata Lamk., in South Africa. The objective of this study was to determine the extent of harvesting in the Mngazana mangrove forest, using available aerial photographs and ground surveys. At 19 sites where harvesting was evident the number of juveniles, adults and stumps were counted in three replicate 25m2 quadrats. GIS was used to generate maps, which indicated that approximately 80% of the mangrove forest showed signs of medium to high harvesting intensity, and that harvesting was taking place in easily accessible areas, especially where Rhizophora mucronata was the dominant species. The ESRI ArcMap density function was used to illustrate the number of harvested stumps and adults within a specific area. GIS analyses classified the mangrove area according to three harvesting intensity classes: low intensity with a ratio of adults to stumps of 2:1, medium intensity 1:1 and high intensity 1:2. According to the classes, 21% of the mangrove area was classified as harvested at low intensity, 35.5% was medium intensity and 43.5% was high intensity. The results indicate that areas dominated by Rhizophora mucronata showed a high intensity of harvesting, while areas where Avicennia marina was dominant showed a low intensity of harvesting. The information from this study can be used to make recommendations for the conservation and management of mangroves in the estuary. In a management plan, access to areas where harvesting is concentrated should be controlled so as to minimise impacts and to allow regeneration to take place.