The mangrove carbon cycle- influence of below-ground processes and managed cutting

INTRODUCTION Mangroves are tropical forests that grow in salty water, usually at the coast. They are valuable ecosystems, providing wood for fuel and timber, habitat for fish, birds and invertebrates and physical protection against shore erosion and storm surges. Mangroves also trap carbon from the atmosphere in the form of peat, which is stored below ground in the wet sediments where they grow; there is still much to learn about this process. Despite their importance they are suffering high rates of destruction, as people clear them for shrimp farming, timber extraction and other uses. Many nations, including Kenya, are looking at better ways of managing their mangrove resources, such as allowing controlled cutting of these forests followed by re-planting. It is important that any such management maximises the ecological benefits of the forests and minimises any ecological damage - for example, management should ensure that below-ground carbon stocks are maintained and that the emission of greenhouse gases is minimised. AIMS This research has two related aims, both focused on a better understanding of carbon cycling and greenhouse gas emissions in mangroves: 1) To examine how controlled cutting, which reproduces on a small scale the commercial cutting that has started again in Kenya, affects carbon stored below the ground and greenhouse gas emissions, along with other factors of importance to a healthy mangrove ecosystem such as the communities of fish and crabs that live there. 2) To determine the sources of carbon dioxide and other greenhouse gases that are lost from the soil in mangrove ecosystems - for example, whether this is coming mostly from the respiration of the roots or from decomposition of organic matter in the soil. We will also determine the productivity of mangrove roots, allowing us to estimate how quickly such roots can grow and trap carbon. In addition to these main aims, we will also be training Kenyan scientists and involving a local women's group and school children in mangrove education and restoration events. FIELD SITE This research will be conducted at Gazi Bay, some 60km from Mombasa on the coast of Kenya. The bay is fringed by a coral reef, and contains seagrass beds and mangrove forests. Gazi village next to the bay is home to 1000 people who use their mangroves for a wide range of products. METHODS Using a natural forest we will clear 5 small areas of trees and compare the greenhouse gas emissions and root decomposition in these with control forested plots. By studying stable isotopes, natural chemical markers in the gases, we will be able to differentiate broadly between the possible sources of the gases coming from our plots. We will also monitor the effects of the cutting on crab and fish communities, and on the ability of the mangrove forests to trap sediment and to retain a stable height above sea level. All the cut areas will be replanted with trees grown by local people in a nursery, and the local school and women's group will participate in a 'mangrove day' of replanting and education.