Temporal mangrove dynamics in relation to coastal development in Pacific Panama

https://doi.org/10.1016/j.jenvman.2005.02.004Get rights and content

Abstract

This study assessed the changes in extent of fringing mangrove located in Punta Mala Bay, Panama in relation to coastal development over a period of two decades. Punta Mala Bay was chosen for this study, due to its social importance and its biological significance, as it is one of the few mangrove areas left around Panama City. Fieldwork confirmed the importance of Laguncularia racemosa in the bay, which formed nearly monospecific stands with a large number of seedlings indicating that the forest was rejuvenating. The mangrove was mapped from 1980 to 2002 using digitised aerial photographs and a GIS was used to determine the location and rates of mangrove growth and loss before and after the construction of a road and water treatment works in 1998. The land use maps were produced with an overall accuracy of 83.8%. The user's accuracy of the maps for L. racemosa dominated stands was 89.7%, although the producer's accuracy was lower due to the omission of seedlings on intertidal areas. It was found that the mangrove was spatially dynamic and had grown substantially in the bay at a rate ranging from 6 to 215% per year until the construction commenced. Between 1997 and 2002 there were 100% loss of mangrove in some areas due to the coastal development. The resilience of the dominant species L. racemosa at this locality was shown by the continued growth of two mangrove zones during the construction period 1997–2002, with one zone increasing in area by 61%. The pioneering ability of L. racemosa after disturbance was demonstrated by the development of two new mangrove zones of 498 and 1254 m2 on bare intertidal areas after construction finished. Future mapping and fieldwork could provide information on the development of mangrove communities and their response to reoccurring human impacts.

Section snippets

Study site

The discontinuous fringing mangrove of Punta Mala Bay, Panama City within the Bay of Panama (08°56′45″N, 079°33′10″W) was the study site in this investigation. Punta Mala Bay is approximately 8.3 ha in size and is located to the west of the city, towards the entrance to the Panama Canal. The Gulf of Panama is characterised by wet and dry seasons, with the wet season lasting from May to December (average monthly rainfall 350 mm) and the dry season occurs between January and April (Glynn, 1972).

Forest structure in plots surveyed

A summary of adult and seedling parameters derived from the field data is given in Table 1. All plots contained adults, saplings and seedlings. Plot 3 had the greatest number of stems over 1 m high (adults plus saplings =201), although this was closely followed by plot 1, which had 186 stems. Additionally plot 1 also has the greatest stand basal area of 0.049 m2 in comparison to a slightly lower value of 0.039 m2 in plot 3. The lowest number of stems over 1 m was in plot 5, which also had the

Discussion

One of the most notable factors to emerge from this study is the dominance in Punta Mala Bay of L. racemosa with A. germinans and R. mangle present in small numbers. This is contrary to Jiménez (1994) who stated that this species was not commonly found on the Pacific coast of Panama. Results presented here and observations in Coiba Island located in western Pacific Panama (H. Guzman 2002, pers. obs) show that L. racemosa can colonise this area when conditions are suitable. This dominance is not

Conclusions

This study showed the dominance of L. racemosa at all intertidal levels of Pacific Panama, in contradiction to some previous studies on the distribution of this species. The value of aerial photography as a means to evaluate coverage by mangrove and spatial vegetation dynamics over time was demonstrated. The use of historic aerial photography in conjunction with forest structure data indicated that mangrove was undergoing normal rejuvenation and is recovering naturally from the intense coastal

Acknowledgements

We would like to thank all those at the Smithsonian Tropical Research Institute, Panama for their help during this project, especially Carlos Guevara and Franklin Guerra who assisted with fieldwork. Subsistence and travel costs for S. Benfield were funded by a NERC Studentship, Heriot-Watt University's Alumni Fund and an internship from the Smithsonian Tropical Research Institute. Additionally, we would like to thank the constructive points of the two anonymous reviewers that helped to improve

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