Four decade vegetation dynamics in Sri Lankan mangroves as detected from sequential aerial photography: A case study in Galle
In remote sensing, aerial photography is often indispensable, particularly in species-diverse mangroves, to identify species or genera or the typology of assemblages. Aerial photographs constitute a most valuable tool to study the dynamics of mangrove forests on a typology basis. They usually constitute the only retroactive basis of comparison to actual mangrove vegetation data. In the present study the dynamics of a mangrove area in southern Sri Lanka, namely Galle (06°01′N, 80°13′E), was investigated using sequential aerial photographs (1956, 1974 and 1994). To identify species or genera from aerial photographs a reliable determination key based on photographic features is needed. For the purpose of this study, a key proposed by Verheyden et al. (submitted) was used. Identification of species and genera from aerial photographs and a study of vegetation dynamics revealed that four sectors, each characterized by a particular vegetation dynamic, could be identified. Characteristic changes in these sectors consisted of either minor changes in composition, mangrove area increase or decrease, or major structural change. Furthermore, the results show that a dynamic interaction between mangroves and Cocos nucifera stands exists in the area. Ground truthing in each of the mangrove sectors confirmed the aerial photography interpretations. Quantitative and qualitative comparisons of field data on adult, young and juvenile trees result in a prediction of a transition of the Excoecaria dominated mangrove to a Bruguiera dominated one in one part, and an evolution towards a terrestrial vegetation elsewhere. These results point at fundamental floristic and structural changes in the mangroves of Galle, in a time scale of decades, both when comparing to the past and when predicting the future.
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Document Type: Research Article
Publication date: 2000-09-01
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