NO. 240 ATOLL RESEARCH BULLETIN 240. Man atad the Variable Fulnerability ofIslan8 Life. A Study afReceni Vegetation Change in the 23ahuma-s by Roger Byme ATOLL Life. Issued hy THE SMITHSONLAN INSTITlJTION Washington, D. C., U.S.A. January 1980 ACKNOWLEDGEMENT The Atoll Research Bulletin is issued by the Smithsonian Institution, as a part of its activity in tropical biology, to place on record information on the biota of tropical islands and reefs, and on the environment that supports the biota. The Bulletin is supported by the National Museum of Natural History and is produced and distributed by the Smithsonian Press. The editing is done by members of the Museum staff and by Dr. D. R. Stoddart. The Bulletin was founded and the first 117 numbers issued by the Pacific Science Board, National Academy of Sciences, with financial support from the Office of Naval Research. Its pages were largely devoted to reports resulting from the Pacific Science Board's Coral Atoll Program, The sole responsibilitv for all statements made by authors of papers in the Atoll Research Bulletin rests with them, and statements made in the Bulletin do not necessarily represent the views of the Smithsonian nor those of the editors of the Bulletin. F. R. Fosberg Ian G. MacIntyre Me-H, Sachet Smithsonian Institution Washington, D,C. 20560 D, R, Stoddart Department of Geography IJniversity of Cambridge Downing Place Cambridge, England ATOLL RESEARCH BULLETIN NO. 240 January 1980 TABLE OF CONTENTS --Page TABLE OF CONTENTS iii LIST OF FIGURES v LIST OF TABLES viil ------Secti3n I. INTRODUCTION i 11. THE THEME: MAN AND THE VULNERABILITY OF ISLAND LIFE 3 Early Interpretations 3 Recent Views 5 Unresolved Issues 9 111. THE SETTING: A LOW LIMESTONE ISLAND 11 Insularity 13 Geology and Geomorphology 13 Soils 19 Climate 2 1 Hydrology 23 The Environment as a Whole 23 IV. THE PRESENT VEGETATION: A GENERAL VIEW 25 Salt-Water Habitats 27 Man1 s Impact 33 Seasonally-Flooded Fresh-Water Habitats 35 Man's Impact 37 Well-Drained Fresh-Water Habitats 39 V, CLEARING AND BURNING FOR AGRICULTURE 49 The Island Arawak 49 The English 5 1 The Free Negr2 53 Contemporary Agriculture 55 VI. SELECTIVE CUTTING OF INDIVIDUAL SPECIES 59 Dyewoods 59 Barks 6 1 Timber Trees 62 Local Exploitation 6Q VII. THE INTRODUCTION OF ALIEN PLANTS AND ANIMALS 67 Introduced Plants 67 Domesticated Animals 7 1 ----Section ---Page VIII. METHODS OF ANALYSIS Field Methods Analysis of Field Data Limitations of Field Data IX. THE IMPACT OF SHIFTING AGRICULTURE: AGE DIFFERENCES IN THE WOODLAND 89 The Whiteland 89 The Flatland 96 The Blackland 103 THE IMPACT OF SELECTIVE PRESSURES: AGE DIFFERENCES IN THE WOODLAND 113 Goats and the Woodland 115 Selective Cutting 122 Combined Selective Pressures 126 XI. THE INVASION OF ALIEN PLANTS 131 The Species Inv3lved 131 The Extent of the Invasi2n 133 XII. THE STABILITY OF THE WOODLAND 141 Adaptati~nsto Clearing and Burning 14 1 Resistance t3 Grazing and Browsing 149 Resistance to Invasion by Alien Plants 150 The Significance of Diversity 151 The Nature of Insularity 152 The Variable Intensity 3f Man's Impact 153 REVIEW AND CONCLUSIONS ACKNOWLEDGMENTS BIBLIOGRAPHY A Systematic list ~f the Plant Species Encountered on Cat Island 175 Index t3 Common Names of Plants Menti3ned in the Text 191 Data Sheet Used During Analysis 3f Old Fields 195 IV. A List of the Minar Species Encountered in each Habitat-Type and Age-Class 197 iii LIST OF FIGURES Figure Page Map 3f the Bahama Islands Lacation Map of Cat Island Geamorpholz~gicalCrass-Sectian of Cat Island Map af Cat Island Shawing Majar Habitat-Types Phz~tz~graphsh3wing Caastal Vegetation an H313cene Beach Ridges Phat3graph sh3wing Coastal Vegetati3n On H313cene Dunes Phat3graph showing Vegetation 3n a Leeward Lirnest.3ne Caast Phat3graph showing Vegetation on a Exposed Limestone Coast Phat3graph shawing a -----Rhizaphara Forest Pho tograph showing Tid a1 Channel Vegetation Ph3t3graph sh3wing C7rnpetitign Between Casuarina and Gundlachia Phot3graph *~f?'Hamm3ckg' Vegetati3n in the KcQueens Savanna Ph3 tograph 3f Recently Burned Palmettaes Ph3tz~graph3f "F3atpath Distribution" af Palrnet toes Aerial Phot3graph af the Waadland Photograph .3f the W33dland 133king east tawards Freetawn Figure Page 18. Ph3t3graph of the Whiteland being Cleared 19. Phot3graph of a Whiteland Field Ten Years after Cultivatic~n 20. Photograph of a Flatland Field Close to the Savanna 21. Photograph of Second Growth Vegetati.3n on the Flatland 22. Photograph of a Severely Burned Blackland Field in 1967 23. Phot3graph of a Severely Burned Blackland Field in 1970 24. Diagram sh.3wing Aerial Phot3graph Reference Grid 25. Whiteland Successi3n Diagram 90,91 26. Aerial Photagraph of Whiteland, 1943 94,95 27. Aerial Phot2graph of Whiteland, 1958 94,95 28. Flabland Successi3n Diagram 97,98 29. Aerial Photograph 3f' Flatland, 1943 100,101 30. Aerial Ph3t3graph of Flatland, 1958 100,101 31. Blackland Successi3n Diagram 104,105 32. Aerial Phot2graph 3f Blackland, 1943 106,107 33. Aerial Photograph of Blackland, 1958 106,107 34. Graphs sh3wing Diversity and Height against Age, for each Habitat-Type 35. Map sh3wing Distributian of Distance Classes 114 36. Phot3graph (1 showing Impact of Grazing by Goats Figure Page Photograph (2) showing Impact of Grazing by Goats 116 Graphs sh3wing Age/Distance Unpalatable Species 118 Graphs showing Age/Distance Distributi3ns 3f Selectively-Cut Species, and ---Metopium -----toxiferum Photagraph showing a Carn Field Infested with Leucaena leucocephala Ph3t3graph sh3wing ------Leucaena leuc3cephala being Outgrown by Native Species Ph3t3graph of a Recently Burned Blackland Field Phat3graph of a Tw3 Year Old Blackland Field Photograph of the Savanna/W3odland Transiti3n Phatograph of the Mangr3ve/Woodland Transiti3n Diagram sh3wing the Floristic Carnp.?sitian across a L3w Limestane Ridge LIST OF TABLES Table Page 1. Climatic Data 1952-1962 The Bight, Cat Island 2 1 Vegetation and Habitat-Types 26 Age and Tonal Density 84 The Number of Fields Sampled in Each Category Species Included in the Analysis of Browsing by Goats Species Included in the Analysis of Selective Cutting Diversity, Distance and Age Percentage Cover A1ien Species Area and Population of Small bJest Indian Islands, 1950-1958 MAN AND THE VARIABLE VULNERABILITY OF ISLAND LIFE. A STUDY OF RECENT VEGETATION CHANGE IN THE BAHAMAS 1 by Roger Eyrne I. INTRODUCTION A question of increasing concern to scientists and I2y- men alike is to what extent plant and animal communities can withstand disturbance by man. In this context the histori- cal biogeography of small i sl ands is especially relevant, Island life has proved to be particularly vulnerzble to human disturb2nce. In the brief period of human settlement faunal extinction rates have been proportionally much higher on islands than on the continents. For plants the situation is less clear. Few island studies have dealt in detail with the consequences of man's impact and as a result the vulner- ability of insular plznt communities is poorly understood. It was with this general problem in mind that the present study was undertaken, Vore specificzlly, an attempt was made to determine the extent to which man has modified the vegetation of Cat Island, a small island in the Bahamas, Originally, it was intended to deal with the vegetation of the island as a whole, but for several reasons the detailed analysis was limited to the mixed evergreen-deciduous woodland, or 'tcop- picevf as it is locally known. The woodland covers more than 90 percent of the island and has been intensively disturbed by man. On a theoretical level the question was considered as to whether or not the vegetation of offshore islands such as Cat is vulnerable in the same way as that of the Hawaiian Islands or the Galapagos. The choice of Cat Island was to a certain extent fortuitous. As a low-limestone island it provided a comparatively simple setting, it was reasonably 7. Yresent address: Department of Geography, Universi- ty of California, Berkeley, California, 94720. (nAanuscript received November 19 78--Eds. ) accessible, and like the Eahamas as a whole its vegetation was virtually unexplored. Field work was carried out during three visits: July to October 1967, June to August, 1968 and June to September 1970. In addition short visits were made to three other Bahamian islands: Bimini , Mayaguana, and New Providence. Historical evidence was gathered in London during the spring of 1968. Particular attention was paid to the manuscript collections at the Public Records Office, the British Museum, the Eritish Museum of Natural History, and the Royal Botanical Gardens at Kew. This text represents a revised version of a doctoral dissertation submitted to the Univer- sity of Wisconsin in 1972 (Eyrne, 1972). 11. THE THEME: MAN AND THE VULNERABILITY OF ISLAND LIFE The idea that island life is inherently vulnerable to disturbance by man was first proposed by Charles Darwin as supporting evidence for his theory of natural selection. Since Darwin's time, however, the whole question of insular vulnerability has been variously interpreted and as yet there is no consensus. Early Interpretations During his voyage on the Beagle (1831-1836), Darwin was particularly impressed by the extent to which man had dis- turbed the plant and animal life of so many remote islands. On St. Helena, for example, the woodland had been virtually removed by the combined effects of selective cutting and grazing, and the native plants had been apparently replaced by introduced species. The many imported species must have destroyed some of the native kinds; and it is only on the highest and steepest ridges that the indigenous flora is now predomingnt (Darwin, 1839: 485). In his account of the voyage, Darwin made no attempt to explain why the plants and animals of remote islands should have been so vulnerable to disturbance.