Andros, the largest island in the Bahamas, has been invaded by Australians. Towering over the locals, they are taking over the beach, pushing out Bahamian residents from the interior and generally causing havoc.
An Australian Invasion
But it's not Australian tourists that are causing concern. It's the Australian pine tree (Casuarina equisetifolia), which is destabilising the coastline by causing erosion of the soil and taking over the habitats of important endemic species. Australian pine, also known as ironwood, beefwood, she oak and horsetail, is a deciduous tree with a soft, wispy, pine-like appearance, which grows 5-10 feet per year to a maximum of 100 feet or more. Once established, it radically alters the temperature, light, and soil chemistry of beach habitats, and inhibits the growth of native dune and beach vegetation, vital for coastal ecosystems. Unlike native shrubbery, the thick, shallow roots of Australian pine make it much more susceptible to high winds, leading to increased beach and dune erosion and interference with the nesting activities of sea turtles.
Drifting in on wind or water from Florida, only 50 miles to the west of the Bahamas, dumped by nurseries after being outlawed in the US, or imported by resorts as cheap landscaping alternatives to endemic species, invasive plants such as the Australian pine have spread wildly without the presence of any natural enemies to limit their reproduction or growth. Capable of flowering year-round, the pine can produce large numbers of small, 'winged' seeds which are dispersed by wind. At present there are no biological controls available, meaning that each individual tree has to be removed manually.
Because communities in the Bahamas were traditionally far apart (there are 700 islands and cays in the archipelago spread out over 124,000 square miles), they needed to be highly self-sufficient. With no doctors or hospitals within easy reach, 'bush medicine' - such as the use of the 'stopper' plant to halt diarrhoea among children - was vital.
Now this rich cultural tradition is being lost as native plants decline and Bahamians leave isolated communities to seek work in the cities. Sea lavender (Tournefortia gnaphalodes), for example, with its small white flowers, is already extinct in Florida and is now at risk in the Bahamas. It can't be grown from seed as it only germinates in hurricanes and storm events, and is therefore totally dependent on natural environments like the beaches of Andros and other Bahamian islands.
As part of the project 'Coastal Ecology of the Bahamas', Earthwatch scientists Dr. Kathleen Sullivan Sealey (University of Miami) and Lester Flowers (College of the Bahamas) are helping local communities in the long battle to reclaim the land for native species, by encouraging individuals and resort owners to remove invasives from their property. Earthwatch volunteers are also assisting with a restoration project just behind the beach. Originally this area would have been home to around 60-70 species of small trees and shrubs, providing a good buffer zone for hurricanes.
The volunteers use a compass and GPS receiver to lay out 10m x 10m plots, then weed them of invasive alien plants to see if native species can make a comeback. The diversity and growth of plants in each plot will be scored throughout the project to assess its effectiveness. Meanwhile research into the diversity of fish, corals and algae on North Andros and Great Exuma islands will help to correlate alterations in beach vegetation with corresponding changes in the nearshore marine environment.
The scientists and volunteers are also drawing on local knowledge of native plants to build a specimen library of culturally and environmentally significant plants. And data gleaned from the project on the ground is being used to 'ground truth' a satellite map of the location and abundance of invasive plants on the islands, which will be made available to the Bahamian government to assist in the management of invasive species throughout the archipelago. Now in its third year, the Earthwatch project continues to study the dynamic shorelines of the Bahamas in order to discover how we can learn to live compatibly with the landscape, and preserve these beautiful but fragile islands for present and future generations.
Julie Meikle participated in the Coastal Ecology of the Bahamas expedition in June 2004.