Allertonia the Vegetation of Eastern Samoa1 W
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ALLERTONIA THE VEGETATION OF EASTERN SAMOA1 W. ARTHUR WHISTLER^ CONTENTS Page Introduction .......................................................................... 46 Review of the Literature ................................................................ 47 Descriptionofthestudy Area ........................................................... 53 Geologyand Soils ................................................................... 55 Climate ............................................................................. 56 Vegetationand Flora ................................................................. 61 Methods Used ......................................................................... 61 Selection of Sites .................................................................... 61 Size. Shape. and Arrangement of Plots ................................................. 61 Identification of Species .............................................................. 63 Collectionof Data ................................................................... 63 Analysis of Data ..................................................................... 65 Community Analysis Results ............................................................ 67 Cluster Analysis ..................................................................... 67 Tabular Comparison ................................................................. 68 OrdinationGraph .................................................................... 74 The Climax Vegetation of Eastern Samoa ................................................. 76 Littoralvegetation ................................................................... 77 1. Lepturus Rock Strand ............................................................ 81 2.Ipomoea Sandstrand ............................................................ 83 3.LittoralShrubland ............................................................... 85 4. Pandanus Littoral Scrub .......................................................... 90 5.Mixed Littoral Forest ........................................................... :91 6. Pisonia Littoral Forest ........................................................... 94 7. Barringtonia Littoral Forest ....................................................... 96 Wetlandvegetation .................................................................. 98 &Coastal Marsh .................................................................. 98 9. Mangrove Forest ................................................................ 101 Rain Forest Vegetation ............................................................... 105 10. 'Au'auli (Diospyros spp.-Syzygium spp.) Coastal Forest ............................. 106 11 . Asi (Syzygium inophylloides) Ridge Forest ......................................... 110 12. Mamala (Dysoxylum samoense) Lowland Forest .................................... 112 13. Tava (Pomeria pinnata) Lowland Forest ........................................... 116 14. Maota-mea (Dysoxylum hunrii] Montane Forest ..................................... 11 8 15. Fega-vao (Syzygium samoense) Cloud Forest ....................................... 121 Scrubby Summit Vegetation ........................................................... 125 16. MontaneScrub ................................................................. 125 Disturbed Vegetation and Forest Dynamics ............................................... 129 Types of Disturbed Vegetation ......................................................... 130 ].Managed Land .................................................................. 130 2. Kula (Dicranopteris) Fernland ..................................................... 13 1 'This paper is part of a dissertation submitted to the University of Hawaii in December. 1979. in partial fulfillment of requirements for the degree of Ph.D. Most of the field work was carried out by the author while he was working on a project for Environment Consultants. Inc., of Dallas. Texas. The project was funded by the U.S. Fish and Wildlife Service (Department of the Interior Contract No. 11-16-0001-5782FA) and resulted in a report entitled An Inventory of the Wildlife and Wildlife Habitats of the Islands of American Samoa. Much of the raw data of the present paper has been taken from that inventory. I wish to thank the members of my Dissertation Committee. and especially Dr. Dieter Mueller-Dombois. for their invaluable guidance during the progress of this research. 2Present address: Department of Botany. University of Hawaii. Honolulu. Hawaii 96822. ALLERTONIA CONTENTS (continued) Page 3.Disturbed Forest ................................................................. 133 4.Rhus Secondary Forest ............................................................ 138 Forest Dynamics ...................................................................... la Lowland Forest (Vegetation Type IX) ................................................. 141 Montane Forest (Vegetation Type VIII) ................................................ 144 Secondary Forest (Vegetation Type VI) ................................................ 146 Population Trends in Monodominant Communities ..................................... 148 Summary .............................................................................. 150 Littoralvegetation .................................................................. 150 Wetlandvegetation ................................................................. 151 Rain Forest Vegetation .............................................................. 151 Scrubby Summit Vegetation .......................................................... 153 Disturbed Vegetation ................................................................ 153 Stability in Climax Forests ........................................................... 154 The Need for Further Research ....................................................... 155 Literature Cited ........................................................................ 156 Appendix I. Checklist of the native and naturalized flowering plants of Eastern Samoa, including species distributions by island. ................................................................ 159 Appendix 11. Raw table of the relative dominance figures from the 37 forest plots in the USFWS inventory. ............................................................................ 164 Appendix 111. Tree data for the 37 forest plots sampled during the USFWS inventory. ...........168 Appendix IV. Fusions of the 37 forest plots of Eastern Samoa using dendrogram analysis on the USFWS data. ................................................................................ 188 Appendix V. Modified X and Y coordinates for the ordination graph (Figure 9) of the 37 forest plots sampled in the USFWS inventory. ...................................................... 189 Appendix VI. Summary of the Is values for the 37 forest plots of Eastern Samoa, based on the USFWS inventory data. ....................................................................... 190 INTRODUCTION This study deals with the vegetation of the islands of Eastern Samoa. Although these islands are usually referred to politically as "American Samoa", the two terms do not exactly coincide. Swains Island, administered as part of the Territory of American Samoa, is excluded from this study, since it is geographically, ethnically, and floristi- cally a part of the nearby Tokelau Islands; it will be dealt with in another paper. The field research for this investigation was carried out between November, 1971, and May, 1979, during a series of visits to the islands. The field work involved nearly 24 months in Samoa, during which time more than 4,000 collection numbers were obtained. The bulk of the work, however, was carried out between May and December, 1976, during a two-year inventory conducted for the U.S. Fish and Wildlife Service (USFWS). The final report, entitled An Inventory of the Wildlife and Wildlife Habitats of the Islands of American Samoa (Contract no. 11-16-0001-5782FA), has been completed but is still unpublished. The information contained in the present study is largely based on this inventory but is more comprehensive, due to further field work and analyses of data. Until the USFWS inventory, there had been very little research done on the vegetation of either Eastern or Western Samoa. With this in mind, the following four objectives were used to guide the research upon which the present study is based: (1) To work out a system for identifying the plant communities by characteristic species composition; (2) To document the reality of the recognized communities by tabular statistics, mathematical methods, and vegetation mapping; WHISTLER: VEGETATION OF EASTERN SAMOA (3) To determine the major environmental variables underlying any of the emerging community patterns; (4) To test to what degree the community and environmental patterns developed in Eastern Samoa can be extrapolated to Western Samoa. The present study of the vegetation of Eastern Samoa distinguishes different types of vegetation on the basis of floristic, structural, and habitat characters. Each com- munity type is described in terms of structure and floristic composition of the forest trees, ground cover, epiphytes, and lianas. Floristic data from a series of 41 study plots have been analyzed and are used to support the delineations and descriptions of the divisions of the vegetation. REVIEW OF THE LITERATURE