Categorisation of land-cover and land-use adjacent to a Sri Lankan mangrove lagoon using object-based classification: state-of-the-art

This research deals mainly with the changes in land cover and their impact on the environment (the soil, the infiltration and drainage of water, evapotranspiration, flora and fauna) in and around Chilaw Lagoon, a Sri Lankan mangrove site. This requires research on the space-time dynamics in soil use and land cover to estimate and predict the human influences on the ecological changes. It examines how the fishing and the shrimp farms can (co-)exist on a sustainable manner in particular. A tool getting more and more crucial in the detection, description, quantification and observance of changes in the landscape and land use, is remote sensing (e.g. Dahdouh-Guebas et al., 2005a). In combination with geographical information systems (GIS) and field work, this is an effective management tool, particularly useful in the detection of ecological degradation (Dahdouh-Guebas et al., 2005b). It is very important to detect cryptic ecological degradation to mitigate loss of ecological functions, such as the protection function of mangroves (Dahdouh-Guebas et al., 2005c; Dahdouh-Guebas and Koedam, 2006). In addition, mangroves function as a source for timber and non-timber forest products for subsistence users, and as a nursery for numerous marine species (Ewel et al., 1998). Our research implements the following activities: (1) Characterisation of the actual land cover by means of remote sensing (Ikonos images) before the field work; (2) Verification on the field of the results of the image classification: land cover, land use, habitats, vegetation assemblages, individual species; (3) Field work on the vegetation structure; (4) Evaluation of the perception of the local population concerning the actual situation of the wood and fishery resources and in particular the cultivation of shrimps; and (5) By analysis of the image processing, the ecological footprint of the shrimp farms and the fishery, a calculation will be attempted of the area of the mangrove forests that are needed for a sustainable management of the shrimp farms and of the mangrove forests. There appears to be a conflict between the shrimp farms and the mangrove forests. One cuts down mangroves to build shrimp farms. But, on the other side shrimp farms cannot survive without mangroves because the gravid females used for stocking the shrimp ponds are dependent on the mangroves. A first expected result is an extensive classification of a very high Ikonos satellite image of Chilaw-Lagoon, with an interpretation key. This will give a good view on land cover and land use in the lagoon which will be used for land management. A second expected result is to give guidelines, based on the ecological footprint of shrimp farms, for reforestation of mangroves. And by this way to give a solution for the conflicts between adjacent land use. The research is ongoing, but this presentation discusses the state-of-the-art in the light of the above objectives and the expected results

Modelling mangrove propagule dispersal: sensitivity analysis and implications for shrimp farm rehabilitation

info:eu-repo/semantics/publishedHexennial International Conference ‘Meeting on Mangrove ecology, functioning and Management – MMM3’, 2-6 juillet, Galle, Sri Lank

Changes in mangrove vegetation area and character in a war and land use change affected region of Vietnam (Mui Ca Mau) over six decades

Aerial photographs and satellite images have been used to determine land cover changes during the period 1953 to 2011 in the Mui Ca Mau, Vietnam, especially in relation to changes in the mangrove area. The mangrove area declined drastically from approximately 71,345 ha in 1953 to 33,083 ha in 1992, then rose to 46,712 ha in 2011. Loss due to herbicide attacks during the Vietnam War, overexploitation, and conversion into agriculture and aquaculture encouraged by land management policies are being partially counteracted by natural regeneration and replanting, especially a gradual increase in plantations as part of integrated mangrove-shrimp farming systems. The nature of the mangrove vegetation has markedly been transformed over this period. The results are valuable for management planning to understand and improve the contribution of mangrove forests to the provision of ecosystem services and resources, local livelihood and global interest

Disentangling the effects of global climate and regional land-use change on the current and future distribution of mangroves in South Africa

The mangrove distribution in South Africa is fragmented and restricted to small forest patches occupying only 16 % of the estuaries within the current range. In this study we used species distribution models to test (1) whether the absence of mangrove forest and its species (Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata) within their current range is driven by climate or by climate combined with human or geomorphic perturbation and (2) how climate change may potentially affect the latitudinal limit of the mangrove forests and its species in South Africa. We used three modelling techniques (generalized linear models, generalized additive models and gradient boosting machines) and a set of three climate-based predictive variables (minimum air temperature of the coldest month, waterbalance and growing-degree days) combined separately with an index of human or geomorphic perturbation. Climate variables for the future projections were derived from two general circulation models driven by two socio-economic scenarios (A2a and B2a). Within the range of the mangrove forest, the fragmented distribution of the mangroves in South Africa was not explained by our set of climate variables alone. The index of human perturbations slightly improved the predictions but the index of geomorphic perturbation did not. Climate change will create climatically suitable sites for the mangrove forest and the two species A. marina and B. gymnorrhiza beyond their current limits, but model outcomes did not agree on the future potential distribution of R. mucronata. We were able to successfully predict range limits and to detect future climatically suitable sites beyond the current limits. Factors controlling mangrove distribution within its range are still to be identified although absences were partly explained by human perturbations. © 2013 Springer Science+Business Media Dordrecht.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms

Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala-Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on propagule dispersal behaviour. Propagule transport was simulated using a finitevolume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on propagule dispersal patterns. Sensitivity analysis showed that smaller propagules, like the ovalshaped propagules of Avicennia officinalis, dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped propagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the propagules being retained within the vegetation. Only a small proportion (max. 5 %) of propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of propagule dispersal modelling in guiding hydrological restoration efforts that aim to facilitate natural mangrove regeneration.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mangrove floristics and biogeography revisited: further deductions from biodiversity hot spots, ancestral discontinuities and common evolutionary processes

This treatment provides a novel re-assessment of the common biodiversity patterns and evolution of mangrove plants based on the ancestral biogeography, extant floristics and distribution records for all species. It is generally acknowledged that mangrove plants occur where they do in the world because past and current factors have influenced their dispersal, diversification and establishment. Over time, the importance and timing of each factor responsible will have changed notably, especially considering their likely co-occurrence with global processes including continental drift and periods of glacial maxima. The premise here is that all extant taxa arose concurrently from their 17 or so family lineages in response to the same overall influencing factors. Accordingly, the combined distribution and phylogenetic patterns of all mangrove genotypes therefore might have a broadly, common framework for their genesis and dispersal. In this treatment, I test the hypothesis that the evolutionary processes of diversification, divergence and speciation have been driven by largely similar geophysical circumstances and events of isolation and reunion. As such, all phylogenies might have been created from the same chief factors and events, including: land barriers, water separation, and climatic conditions; albeit applied sometimes differently for each of the genetic lineages where mutation rates and dispersal capacities might differ. With such matters in mind, the approach taken has been to thoroughly review known distributional records and patterns, along with assessments of diversity hotspots, spanning large geographic areas, plus species gradients and discontinuities of extant and fossil records. All these are considered tangible evidence of the processes of dispersal and evolution affecting particular mangrove entities. In this way, the combined influence of dispersal, divergence and speciation of the various mangrove plant types, as likely to be the key factors affecting phenotypic variations resulting in their possible, shared patterns around the world. In summary, the integrated role and influence of each taxon has been re-evaluated by comparing matching distributional patterns and common phylogenetic relationships in consideration of key drivers, concurrent physical events and circumstances