Mapping mangroves aids conservation of valuable habitats
Mangroves are globally important habitats, found across the world from South East Asia to the Caribbean. A varied collection of trees and shrubs adapted to a salty intertidal environment, mangroves provide a huge variety of 'ecosystem services'. Mangroves are particularly good at reducing coastal erosion by providing a buffer against the effects of waves, currents and flooding.
In Malaysia, mangroves have been valued at US $300,000 per kilometre for their storm protection and flood control alone. Highly biodiverse, mangroves provide an ideal habitat for fish, shellfish and birds, including many endangered species, as well as food stocks. Another beneficial property of mangroves is their natural filtration system, allowing silt and sediment to settle, filtering out pollutants and retaining nutrients. This makes mangroves some of the most productive habitats on Earth. Threatened by rising sea levels, habitat loss and over-fishing, scientists rapidly need to find a way of protecting these vital resources.
How can we monitor mangrove loss?
Scientists have begun to determine how best to monitor and halt the decline in global mangrove habitat. Recent research, published in Pertanika Journal of Science and Technology compared three techniques which can detect changes in mangrove forest areas. All three techniques were types of "remote sensing technology", allowing scientists to monitor changes in mangrove cover without actually visiting the area. Remote sensing technology is often cheaper, freeing valuable resources to be spent elsewhere, and can be less time consuming. Scientists used satellite images to compare tropical mangrove cover in the Matang Mangrove Perak Forest, Malaysia, over a period of two years. The three techniques compared, all carried out by computer, were:
Image differencing
Images of mangroves from the same area are compared and differences between the images highlighted, to show how mangroves changed over time.
Normalized Difference Vegetation Inde
Images are assessed to determine whether they contain live, green vegetation, which shows whether the area of living mangroves has decreased.
Mutual information
Images of the same area from different dates are compared and assessed to see how similar they are. This is repeated for many images and shows the changes in mangrove cover over time.
Results showed that mutual information was the most reliable way of detecting changes in mangrove habitat, especially in areas where there was already less plant growth. In addition, mutual imaging worked more effectively that the other two techniques when images were taken in different weatherand lighting conditions. Now, scientists hope to use this technique to determine where mangrove loss is occurring quickest and take steps to halt the decline.
Top Image Credit: © jirapong
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