Distribution and density of Leucaena leucocephala on St. Eustatius
This report was commissioned by St. Eustatius National Parks (STENAPA) in order to investigate the distribution and density of Leucaena leucocephala (Tan Tan) on St. Eustatius. L. leucocephala is a very fast growing invasive species. The research was initiated due to species’ presence in large quantities within the national parks and the fact that it possibly threatens native flora due to its competing characteristics.
The research areas consisted of the Quill National Park, Boven National Park and the Miriam C. Schmidt Botanical Garden. Data collection was based on a random sampling design which covered 25 % of the entire research area. Subplots were taken within the random plots containing data on soil cover, canopy cover, density, local area and the number of seedlings, saplings, mature trees and overmature trees. Additional information was collected on all mature and overmature trees within the plots, including height, crown vitality, GPS coordinates and diameter at breast height (DBH).
Results within the National Parks showed that the highest densities are present along the Bergje trail, Venus, the Quill trail and the Miriam C. Schmidt Botanical garden. Lower densities of L. leucocephala appear around the Jenkins bay trail, Gillboa first ridge and the entrance of the Around the Mountain North and South trail. Results indicate a positive correlation between the number of mature L. leucocephala trees and the percentage of canopy cover. A negative correlation was discovered between the number of mature L. leucocephala and the percentage of soil cover.
L. leucocephala was found in multiple sites on St. Eustatius, the majority of these being characterised by road sides, gullies and disturbed areas with an open canopy. Multiple reports state that L. leucocephala was found in areas with similar characteristics as the areas in which L. leucocephala was recorded in St Eustatius. L. leucocephala is very common on bare soil according to the same reports, however the results of this research differs from this trend.
An alternative explanation for the abundant distribution of L. leucocephala on St. Eustatius might be the presence of free-roaming goats. Many goats were observed in areas which contained the highest densities of L. leucocephala, while no goats were observed in almost all areas that were free of L. leucocephala.
Recommend future activities include a long term monitoring program in order to see whether L. leucocephala is spreading within the national parks. Sites that require monitoring are Venus, Gillboa Hill entrance and the gulley between Bergje and the Jenkin Bay trail.
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