Hobdy, Robert

English

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A VEGETATIVE SURVEY OFMAUl COUNTY'S OFFSHORE ISLETSRobert HobdyDept. of Land & Natural ResourcesDivision of Forestry and WildlifeP. O. Box 1015Wailuku, Hawaii 967938788IntroductionOffshore islets in Hawaii present unique opportunities for the study of nativecoastal ecosystems. These offshore ecosystems remain largely intact on the manyislets throughout the State. In this respect they stand in sharp contrast to onshoreareas that have been altered by various influences and activities. They have remainedfree of dogs, cats, rats and mongooses which are serious predators on nesting seabirds,and they have also remained free of the several herbivorous ungulates that have soaltered our onshore vegetation. Furthermore, their isolated locations, rugged topographyand protected status have combined to ensure that human visitation is minimal. Intro-duced weed species are thus usually minor components of the vegetative cover. Onthese islets we can still catch a glimpse of a diverse and interesting coastal florathat once extended throughout our entire archaepelago.Maui County has thirty offshore islets on which biological surveys are beingmade. This includes surveys of seabirds as well as vegetative surveys. Fifteen'of these are located along the north and east shores 6f Maui, eight are located alongthe north and east shores of Molokai, five are on the west and south shores of Lanai,one is on the south coast of Kahoolawe and one, Molokini, lies in the AlalakeikiChannel midway between Maui and Kahoolawe.These islets range in size from Molokini which is 22.4 acres and in heightfrom Okala which rises about 425 feet above the sea to low islets only a fractionof an acre in size. Many other small rocks lie along these coasts, but they are sosmall and low that they are awash in high surf and support no vegetation or suitablehabitat for seabird nesting. These have been excluded from consideration here.Geologically speaking, 26 of the 30 offshore islets fall into the category ofsea stacks, rocky remnants of the original island coastline that have been separatedby erosion over time.These islets are extremely steep and rocky with limited amounts of soil on theBununits and on ledges. They are all located along coastlines facin& the open ocean89where storm wave action has been greatest. The remaining four islets were createdby scparate late stage volcanics. Molokini, Mokuhooniki and Kanaha are tuff coneremnants while Alau Islet near Hana is an old cinder cone. These formations generallyilie further offshore than sea stacks. They form greater quantities of loose soilbut this soil is usually rather sterile and quick to dry out during the dry seasons.Rainfall on these islets varies from about 175 inches/year on the north coastof east Maui to about 12 inches/year on Lanai, Kahoolawe and Molokini. Islet florascorrespondingly vary from lush perennially green representations to examples~ withxeric floras that respond to winter rains with quick growth that rapidly matures and,dries up during the summer months leaving the islets very barren in appearance. ,Results and DiscussionPlant species encountered included a few of nearly universal occurrence, somethat were characteristic of either wet or dry climates and several small isolatedpopulations of very rare species. Collections made have allowed reevaluation ofthese rare taxa. New determinations appear to be in order for some. At least onedistinct new species was discovered as well as perhaps three or four new varietiesor forms.Portulaca oleracca and Sonchus oleraceus were the two plant species found innearly every situation. Their occurrence seems to depend on seabird activity asthey are always found growing in excavated or disturbed soil within seabid colonies.The one islet on which these two species do not occur, Moku Huki, also has no seabirdactivity.Scaevola taccada, Sesuvium portulacastrum and Fimbristylis pycnocephala aretypical of wet islets where they make up a significant portion of the vegetation.None of them, however, occur on the dry islets, Conversely, Sida fallax, Boerhaviatetrandra and Jacqucmontia sandwicensis are typical of dry islets but do not occuron wet islets. Within the range of climates one can find most of Hawaii's halophytic'plant species.90Puu kone yielded two specied of Eragrostis.91One was a xeric form of E. variabilis- ..and the other was a diminutive plant with narrow appressed spikes that is arrnrentlya new species. It is being studied by Dr. Derral Herbst but it has nqt been describedyet.Peucedanum sandwicense var. hiroi was found on Keopuka high on inaccess3blecliffs. This rare plant has only been collected a few times on Maui and only severaldecades ago.ConclusionTo date 19 islees have been visited. Due to the sheer cliffs surrounding manyof them, however, not all have been accessible. Eleven of them were accessibleand for these,· vegetation checklists have been nlade. These are not included but areavailable upon request.facts about each islet.A general information sheet is attached with a variety of.'These surveys will continue until all of Maui County's offshore islets havebeen completed. ·The vegetation information will be combined with seabird informationcurrently being gathered by the U. S. Fish and Wildlife Service and State wildlifebiologists to give us a more complete biological overview. The knowledge gainedwill allow us to better understand these tiny ecosystems and to better protect themin the future.Literature CitedDegener, O. 1932 et. seq. Flora Hawaiiensis.Published privately.Hillebrand, W. F. 1888 Flora of the Hawaiian Islands.Reprinted by Hafner Publishing Co., New York and London, 1965.Annotated and published after the author's death (fascimile ofthe 1888 edition)St. John, H. 1973 List and Summary of the Flowering Plants in the Hawaiian Islands.Pacific Trap. Bot. Garden, Mem. 1. Lawai, Kauai, Hawaii 519 pp.92Table I. MAUl COUNTY'S OFFSlIORE ISLETSGENERAL INFORMATIONAverageHeight Geologic Vegetation AnnualIsland Islet Acreage ** (feet) Formation ~ensity Rainfall USG~_~Re..[erence----Maui Alau 5.0 148 Cinder cone Dense 50" Hana quadranglePu'u ku 1.5 72 Sea stack Moderate 50" Hana quadrangleMoku Pipi 0.9 50* Sea stack Moderate 120" Hana quadrangleMoku Huki 0.3 55* Sea stack Dense 175" Nahiku quadrangleMakoloaka 0.3 85* Sea stack Moderate 160" Keanae quadrangleMoku Mana 1.4 65* Sea stack Moderate 100" Keanae quadrangleMoku Hala 0.3 75* Sea stack Sparse 100" Keanae quadrangleKeopuka 2.2 125* Sea stack Dense 100" KeanaequadranglePapanui 0 kane 2.3 10* Sea stack None 65" Haiku quadrangleHulu 1.5 100* Sea stack Moderate 30" Kahakuloa quadrangleA'awanui 0.5 30* Sea stack None 30" Kahakuloa quadrangleA'awaiki 0.5 50* Sea stack None 30" Kahakuloa quadrangleKaemi 2.5 125* Sea stack Sparse 30" Kahakuloa quadrangleMokeehia 8.5 165* Sea stack Dense 30" Kahakuloa quadrangleMahinanui 1.5 40* Sea stack None 30" Kahakuloa quadrangleMolokai Moku Hoon:iki 14.1 203 Tuff cone Moderate 25" Halawa quadrangleK<lnaha 2.0 110* Tuff cone Moderate 25" Halawa quadrangleMoku Papapa 0.6 10* Sea stack None 30" Halawa quadrangleMoku Manu 2.3 175* Sea stack Sparse 50" Kamalo quadranglePauonuakea 0.5 75* Sea stack Moderate 60" Kamalo quadrangleHuelo 2.4 220* Sea stack Dense 50" Kamalo quadrangleOkala 7.4 425* Sea stack Dense 50" Kama10 quadrangleMokapu 11. 7 360 Sea stack Dense 40" Kamala quadrangleLanai Nanahoa 0.4 128' Sea stack Moderate 18" Lanai IslandKiei 1.0 40* Sea stack Sparse 17" Lanai IslandNoku Naio 0.1 30* Sea stack None 12" Lanai IslandPoopoo 2.1 65* Sea stack Dense 12" Lanai IslandPuu Pehe 1.6 101 Sea stack Moderate 12" Lanai IslandKahoolawe Puu Koae 17.0 378 Sea stack Sparse- 12" Kahoolawe IslandMolokin:!. Molokin! 22.4 160* Tuff cone Dense 15" Maui Island andKahoolawe Island***Acreage calculated by averaging 50 counts using a 256 dots per square inch dot gridHeight approximates from USGS Quadrant maps and personal observations

A vegetative survey of Maui county's offshore islets

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A vegetative survey of Maui county's offshore islets

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