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Ecology and Conservation

Research Report

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Key word: Pratas Island、drift disseminule、vegetation resotration

Pratas Island has undergone human activities such as firewood cutting, mining, and reclamation, and invasion of exotic species like Leucaena leucocephala, results in the fragmentation or degradation of its terretorial vegetation. At present, removement of exotic species and vegetation restoration have been conducted actively. This project suggests protocols for the reference of landscape vegetation restoration and vegetation management via the information of local flora and plant community investigation, ocean floating seeds survey, inspection of exotic species and distribution, vegetation permanent plots, and phenology monitoring works.
The floristic data showed 54 families, 131 genera, 158 species were collected, contain 6 rare species in Pratas Island. Vegetation types were classified into 7 types, namely Pisonia grandis forest, Scaevola taccada shrubland, Pandanus odoratissimus shrubland, Suriana maritime shrubland, Ipomoea pes-caprae subsp. brasiliensis grassland, Sesuvium portulacastrum grassland, Avicennia marina clump. Sea distance, lagoon or sea side, pH value and Kalium are the most important variables influencing species composition and vegetation distribution. Furturemore, 10 permanent samples were setting in the main vegetation type. We suggest the samples should to resurvey for each 5 years to monitor the plant competition and succession.
Assemblages of drift disseminules are investigated from beaches on the Pratas Island. The 53 disseminules taxa were recorded and identified, representing 28 families, 43 genera. There are 37 taxa (72.5 %) drifted from other area, 13 taxa (23.5 %) are dropped from the trees which native or planted on the Pratas Island; 25 taxa (47.2 %) are vital. The pea family (Leguminosea) is the most abundant taxa among the drift disseminules. According the results from the plots survey, 32 disseminules, 16 taxa were recorded. In general, the species richness is high but frequency of species is low. All of the seedlings are native plants, 15 taxa are recorded in the plots and 4 species 15 individuals are the seedlings of woody plants. Our data demonstrated the short term investigation hardly knows the drift disseminule of Pratas Island completely.
There are 75 exotic taxa in Pratas Islands. According to the invation property and distribution, 75 taxa can be divided into cultivated plants (39 taxa), casual alien plants (15 taxa), naturalized plants (7 taxa), and invasion plants (14 taxa). And according to the potential of migration, different suggestions including “temporary no treatment”, “vegetation restoring (for highly exposed land)”, and “removing” are conducted. Accordind to the result of phenology observation of 17 species in Pratas Island, the flowering periods can be divided into “all the year”, “during late winter to early spring”, “during spring and summer”, and “twice a year”. The proper seed collecting time of most afforestation species has been comprehended by current data. We suggest to focus only on certain species to conduct quantitative phenology monitoring.
Protocol of vegetation resotration and afforestation, guidance of plant phenology monitoring, and suggestions of guidance of exotic species control and management of Pratas Island were also documented. These documents can be reference information for works of vegetation restoration and management.