Human-impacted mangroves in Gazi (Kenya): predicting future vegetation based on retrospective remote sensing, social surveys, and tree distribution

Dahdouh-Guebas, F.; Van Pottelbergh, I.; Kairo, J.G.; Cannicci, S.; Koedam, N.

doi:/10.3354/meps272077

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Human-impacted mangroves in Gazi (Kenya): predicting future vegetation based on retrospective remote sensing, social surveys, and tree distribution

Dahdouh-Guebas, F.; Van Pottelbergh, I.; Kairo, J.G.; Cannicci, S.; Koedam, N. (2004). Human-impacted mangroves in Gazi (Kenya): predicting future vegetation based on retrospective remote sensing, social surveys, and tree distribution. Mar. Ecol. Prog. Ser. 272: 77-92. dx.doi.org/10.3354/meps272077

In: Marine Ecology Progress Series. Inter-Research: Oldendorf/Luhe. ISSN 0171-8630; e-ISSN 1616-1599

Available in	Authors
VLIZ: Open Marine Archive 97805 [ download pdf ]

Keywords

Analysis > Mathematical analysis > Statistical analysis > Variance analysis > Multivariate analysis
Aquatic communities > Benthos
Audiovisual materials > Photographs > Aerial photographs
ISW, Kenya, Gazi Bay
Mangroves
Prediction
Maftaha Bay [Marine Regions]
Marine/Coastal; Brackish water

Author keywords

mangroves; dynamics; aerial photography; macrobenthos; multivariate analysis; forecasting; interviews; Kenya

Authors		Top
Dahdouh-Guebas, F., more Van Pottelbergh, I. Kairo, J.G.	Cannicci, S. Koedam, N.

Abstract

Gazi Bay, Kenya, covers an area of 18 km^², and its mangroves are degraded. We present a quantitative and qualitative evaluation of the degradation of vegetation structure and dynamics of mangrove communities over a period of 25 yr, using aerial photography in a geographical information system (GIS), combined with ground-truth data for different vegetation layers, and with faunal and environmental factors. Retrospective analysis and understanding of current practices were aided by interviews with Gazi village elders and by field observations of mangrove tree stumps. GIS-based vegetation maps were combined with data obtained using the point-centred quarter method (PCQM), an accuracy analysis was performed, and forestry parameters were derived from the resultant PCQM data. In addition to general human-induced degradation of vegetation structure and floristic composition of the seaward mangrove zone, a particular sandy beach is expanding at the expense of mangrove, whereas the back mangrove zone has undergone minor changes. Aerial photographs of 1992 and current field data show an apparent zonation of 6 different monospecific or mixed mangrove communities, with a high importance of Rhizophora mucronata in each community and each vegetation layer. Retrospective vegetation structure was combined with correspondence analyses on the PCQM data derived for adult, young and juvenile trees in order to make predictions. Present dynamics initiated by anthropogenic degradation of mangroves continues, even though human impact has diminished. We predict that under a 'no impact scenario', the sandy ridge will continue to expand, that this will speed up under a 'mangrove cutting scenario', and that a scenario altering the complex topography will lead to a major re-organisation of the mangrove and terrestrial vegetation structure.

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