Abstract
Brunei Bay, which receives freshwater discharge from four major rivers, namely Limbang, Sundar, Weston and Menumbok, hosts a luxuriant mangrove cover in East Malaysia. However, this relatively undisturbed mangrove forest has been less scientifically explored, especially in terms of vegetation structure, ecosystem services and functioning, and land-use/cover changes. In the present study, mangrove areal extent together with species composition and distribution at the four notified estuaries was evaluated through remote sensing (Advanced Land Observation Satellite—ALOS) and ground-truth (Point-Centred Quarter Method—PCQM) observations. As of 2010, the total mangrove cover was found to be ca. 35,183.74 ha, of which Weston and Menumbok occupied more than two-folds (58%), followed by Sundar (27%) and Limbang (15%). The medium resolution ALOS data were efficient for mapping dominant mangrove species such as Nypa fruticans, Rhizophora apiculata, Sonneratia caseolaris, S. alba and Xylocarpus granatum in the vicinity (accuracy: 80%). The PCQM estimates found a higher basal area at Limbang and Menumbok—suggestive of more mature vegetation, compared to Sundar and Weston. Mangrove stand structural complexity (derived from the complexity index) was also high in the order of Limbang > Menumbok > Sundar > Weston and supporting the perspective of less/undisturbed vegetation at two former locations. Both remote sensing and ground-truth observations have complementarily represented the distribution of Sonneratia spp. as pioneer vegetation at shallow river mouths, N. fruticans in the areas of strong freshwater discharge, R. apiculata in the areas of strong neritic incursion and X. granatum at interior/elevated grounds. The results from this study would be able to serve as strong baseline data for future mangrove investigations at Brunei Bay, including for monitoring and management purposes locally at present.
Highlights
IntroductionA combination of ground truth and remote sensing data analysis is advantageous for developing the most reliable land-use/cover mapping and thereby useful for making appropriate decisions for conservation and management of natural resources (Kovacs, Wang & Blanco-Correa, 2001; Kovacs et al, 2004; Chauhan & Dwivedi, 2008; Neukermans et al, 2008; Satyanarayana et al, 2011; Leempoel et al, 2013)
The spatial extent of the dominant mangroves was estimated at ca. 35,183.74 ha where N. fruticans occupied the highest land-cover followed by R. apiculata, S. caseolaris, X. granatum and S. alba in the order
Ground inventory revealed the abundance of N. fruticans and R. apiculata as widespread species while S. caseolaris, X. granatum and S. alba as locally distributed species at the river mouth and/or interior/elevated grounds
Summary
A combination of ground truth and remote sensing data analysis is advantageous for developing the most reliable land-use/cover mapping and thereby useful for making appropriate decisions for conservation and management of natural resources (Kovacs, Wang & Blanco-Correa, 2001; Kovacs et al, 2004; Chauhan & Dwivedi, 2008; Neukermans et al, 2008; Satyanarayana et al, 2011; Leempoel et al, 2013). The Point-Centred Quarter Method (PCQM) is recognised as the most appropriate ground-truth for mangrove and remote sensing combinatory investigations (Cintrón & Schaeffer Novelli, 1984; Dahdouh-Guebas & Koedam, 2006; Satyanarayana et al, 2011). The PCQM is efficient for characterising mangrove vegetation and less time-consuming, but it causes minimum damage to the understorey while sampling (Cunningham, 2001; Dahdouh-Guebas & Koedam, 2006)
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