Research Collection Master Thesis Vegetation survey and GIS-based zonation of the Fond d'Albaretz Forest, Praslin, Seychelles Author(s): Farrèr, Claudia; Hertach, Martin Publication Date: 2009 Permanent Link: https://doi.org/10.3929/ethz-a-005791819 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Vegetation Survey and GIS- based Zonation of the Fond D’Albaretz Forest, Praslin, Seychelles Master Thesis in Environmental Sciences Claudia Farrèr Martin Hertach March, 2009 Supervision: Dr. Karl Fleischmann and Prof. Peter J. Edwards Institute of Integrative Biology Zurich Abstract The Seychelles flora displays a high degree of endemism and various endemic woody species are threatened according to the IUCN Red List. The habitats of rare endemic species are often confined to boulder fields and glacis. Threats are competition by invasive species, forest fires and anthropogenic habitat degradation. To preserve habitats it is crucial to understand possible interconnections between the vegetation composition, boulder fields and fire disturbances. We investigated these interconnections in the area of the Fond D’Albaretz on Praslin Island, which is part of a unique ecological framework and shelters large interlinked boulder fields. An extensive database on the vegetation composition was acquired by means of count-plot analysis and trail transecting. Vegetation zonations were conducted in terms of (i) nativeness, (ii) protection values and (iii) presence of red listed species. Connection between the occurrence of boulder fields and palms was studied with a boulder field classification. Spatial data on the occurrence of boulder fields and large patches of the fern Dicranopteris linearis were gained using satellite images, a geographic information system (GIS) and the global positioning system (GPS). We also studied post-fire succession by qualitatively monitoring recently affected areas. To visualize the risk of the induction and the spread of fire, we produced a fire risk map by including topographic, anthropogenic and vegetation-based parameters. Based on prominence values, we found that 75.4% of the vegetation of the Fond D’Albaretz is native and 20.7% is endemic. Twenty-one different endemic species were found, one of which was classified as “critically endangered”, one as “endangered”, eleven as “vulnerable”, five as “near threatened” and three as “least concern”. The vegetation zonation reveals a uniform high protection value of the forest and is therefore comparable to the Vallée de Mai. We found a significant correlation between the presence of big boulders and palms (adults and saplings). We also found a moderate significance for the correlation between the presence of big boulders and threatened species. Interpretation of satellite images and spatial mapping in the field showed that boulder fields cover an area of 46’437 m 2. Resprouting in post- fire-areas is dominated by endemic species. Most of the area of the Fond D’Albaretz shows a high risk of spreading or inducing forest fires. The Fond D’Albaretz is of high ecological importance due to its consistently high protection value, its comparability to the Vallée de Mai and its relics of original low-altitude forest. The extensive boulder fields are a hideaway for threatened plant species and protect them from forest fires. The limited presence of Dicranopteris l. and invasive species suggests that forest fires only rarely affected the Fond D’Albaretz in the past. The protective force of boulder fields against fires, the absence of preceding disturbances and the ecological framework seem to be the main reasons for the high ecological value distinctive of the Fond D’Albaretz. The use of GIS proved to be very valuable and the newly established fire risk map can be used as a measure to effectively fight forest fires in the future. Keywords : Ecological importance, Boulder field classification, Protection value, Vegetation zoning, Dicranopteris l. , Red listed woody plant species, Geographic information system, Fire risk map, Fond D’Albaretz, Praslin, Seychelles. Acknowledgements We would like to thank our supervisors Dr. Karl Fleischmann and Prof. Peter J. Edwards from the Institute of Integrative Biology, ETH, for the possibility to write this master-thesis and for their overall support. Special thanks go to Matthieu and Bart LaBuschagne and their families who made this work possible. Your support with all our daily life and work problems was fantastic. Matt, we thank you for all the adventurous trips in the forest. We have spent an unforgettable time in the Seychelles! Many thanks go also to the staff of the Hotel Coco de Mer for cheering up our days, for cooking and joining us in the staff canteen and for their kindness to provide internet access. A special thank goes to our neighbours Sudarsana Weliwitigoda and Don Jagath Katugampola with his wife Ayomi and their daughter Suchali. Thank you for all the good times we spent at your home, the delicious food and all the nice talks. We will miss you! Many thanks go to the Plant Conservation Action group (PCA) and especially to Katy Beaver, Frauke Fleischer-Dogley and Lindsay Chong Seng for administrative help, accommodation and inputs for our work. It is always a great pleasure to meet you! We would like to thank Victorin Laboudallon for the insightful walk and helping us with identifying species. We are thankful to Justin Prosper from the GIS-Unit at the Policy Planning and Services Division of the Ministry of Environment on Mahé for providing us with all the needed spatial data of Praslin. We are grateful to the Praslin Development Fund (PDF), where we thank the chairman Mr. Michel Gardette for organising us the permit to visit the Fond Ferdinand Nature Reserve and Micheal Gill who was a great guide in the field and helped us to locate former plots. Special thanks go to Patrizia Frei for statistical support, inputs for writing the report and unforgettable two weeks in the Seychelles. We thank Karsten Rohweder and Hans-Heini Vogel from the Institute of Integrative Biology, ETH, for providing us with even in the tropics astonishing good working laptops and for their technical support by finishing our thesis. Last but not least, we would like to thank our parents for their overall support. Content 1. Introduction .................................................................................................................................1 2. Methods ........................................................................................................................................4 2.1 General principles.................................................................................................................................... 4 2.2 Trail transecting........................................................................................................................................ 4 2.3 Count-plot analysis................................................................................................................................... 6 2.4 Photo monitoring.....................................................................................................................................7 2.5 Boulder field classification....................................................................................................................... 8 2.6 Vegetation zoning..................................................................................................................................... 9 2.7 Dicranopteris linearis survey......................................................................................................................13 2.8 Boulder field mapping ...........................................................................................................................14 2.9 Qualitative monitoring of post-fire areas...............................................................................................14 2.10 Fire risk map.........................................................................................................................................15 3. Results ....................................................................................................................................... 17 3.1 Fond D’Albaretz - State of the forest .....................................................................................................17 3.1.1 General findings.......................................................................................................................17 3.1.2 Prominence along trail transects..............................................................................................17 3.1.3 Prominence within sampling plots ..........................................................................................19 3.1.4 Red listed species......................................................................................................................21 3.2 Boulder field classification.....................................................................................................................22 3.2.1 Palms vs. dicotyledonous trees.................................................................................................23 3.2.2 Threatened species vs. invasive species....................................................................................24 3.3.