Enderbury Island
Page 6
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Transcription
C.R. Long 1964 shrubby Sida bushes. The nests are constructed of Sida twigs with Boerhaavia stems and leaves placed in the center. The nests in the dead or weakly sprouting Cordia and Messerschmidtia are composed of Sida twigs piled high. The twigs on the bottom are weathered a gray color while those on top are lighter and appear to have been added at a later time. The Digitaria sp. is much shorter and less vigorous in appearance than that observed on Starbuck. Much of the Sida is prostrate - only at the protected edges of the lagoon or around the outside edge of the brush patches is the Sida upright. Both seedling and adult plants of Sida seem to be frequent in the Sesuvium patches rimming the lagoon (on the north end the Sesuvium has filled in the old lagoon area). The wind seems to be out of the east at this season and almost constant. The brush piles, located toward the rim of the islands must also penetrate deeper for moisture to the fresh water lens below. This lens is subject to greater depletion in the dry lagoon areas and perhaps the lens is contracted during periods of extreme evaporation and dryness. The guano soils and underlying hardpan, and, the salty crusts formed in the lagoon beds may be responsible for the existence of any vegetation available water supplies on these dry islands. The Lesser Frigates nesting in the brush patch "spill over" into open areas on the west side (bare surfaces or some small Sida and Lepturus). Further along this side of the island is a guano mound, guano operation ruins and another brush area with Cordia and Messerschmidtia spp. supporting the nests of Greater Frigatebirds and redfooted boobies. Transect II (starting on the west near old guano diggings - from the shore). sand Triumfetta -> gravel and sand, bare disturbed site Digitaria Sida -> Boerhaavia -> Lepturus dead Cordia Portulaca Cassytha on Sida larger gravel, rocks -> former house sites mid-point of island Lepturus gravel and sand Sida Digitaria Portulaca Sida Portulaca Boerhaavia In the rubble of the old guano operations on the north end of the island the Sida - Portulaca - Boerhaavia association was observed. A few clumps of Lepturus are also present but very sparsely distributed in this area. The distribution of plant species on the north end is non-uniform. On the rocky flats and rolling mounds Boerhaavia is found - suggesting, perhaps, a pioneer species in rocky or heavily gravelled areas. In some of these same areas one finds Portulaca associated with the Boerhaavia. It may be that the perennial Boerhaavia with its seasonal addition of dead leaves and stems and, finally, a dead rootstock of considerable size may contri- bute significantly to the windblown sand (which accumulates between and down below the rocks) - and windblown organic matter to form the necessary soil pockets for the successful sprouting and growing of other species. The Portulaca is shallow rooted and needs a soil which will hold some water content and at the same time be near the sunlit surfaces. In semi-protected areas behind the hillocks you find patches of Lepturus, usually on the east face slopes. In the depressions between the hillocks - in coral gravel and guano soil Sesuvium seems to thrive, but not forming a continuous mat over the