Feb 3, 2016

Australian Invasion: Casuarina induced erosion by Melissa N.

January 2016

On San Salvador, we looked around the island at everything from rock formations to coral reefs. I was interested to learn about the invasive casuarina. This Australian pine was brought to the island (and all of the Bahamas) in hopes of stabilizing coastal dunes during storms. Sadly this pine had the opposite effect.

Australian pines. Image by Meg Stewart https://www.flickr.com/photos/megstewart/4320102993

The casuarina has a shallow root system that can easily be ripped out under the stress of the frequent hurricanes. Once the roots become dislodged, the dune is ripped up giving way to the processes of erosion. The dune eventually loses its profile and becomes unstable.
The casuarina also has needles that cover the ground below the tree. These needles block sunlight penetration to the soil and acidify the soil surrounding the tree. The casuarina not only rips up the dunes, but also halts the growth of any vegetation that could stabilize the dune.

Figure shows a profile of dune erosion caused by cauarinas. Figure by http://www.geraceresearchcentre.com/pdfs/10thNatHist/113_Sealey_10thNaturalHistory.pdf

Photograph of a foreshore on San Salvador Island. Casuarina trees can be seen in the upper right hand corner of the image.

Image shows beach erosion caused by the Australian pine. Photo by https://casuarinacontrol.files.wordpress.com/2011/07/casuarina1.jpg

So what does all of this mean for the island's future? Dunes serve to protect the land in times of storms. Think of them as buffers for local homes located on the coast. When Hurricane Joaquin struck the island on October 2015, it brought powerful winds and swells that eroded sand away from dunes. Beaches on the eastern side of the island were particularly affected. Australian pines are speeding up the erosion process. What can be done about this? For one, the Australian pine has a very dense and heavy wood that withstands water. The trees could be harvested and made into furniture for export which would boost the island's economy and create a market for Bahamian furniture.  

Sources and further reading:

The cycle of casuarina induced beach erosion by Neil Sealey