Vegetation Survey (Week 2)

Our first study location was in an area densely forested with Australian Pines near East Wells Inlet - with an estimated 50 trees within view in our study site. We marked off two parallel 12-meter transects through the area, taking samples at the 0, 6 and 12 meter marks. Using a clinometer and some basic trigonometry we found that the average height of Australian pines we sampled in this area was 42.6 feet. Using the densitometer and again sampling trees at the 0, 6 and 12 meter mark we found that the average canopy cover of for trees that we sampled at this location was about 57.1%. In addition, we used 1 x 1 meter quadrants to sample the remaining native vegetation in the area and found that it covered only .333% of the area sampled, with most of the ground being covered by dead and dry needles. Of the native species sampled, we found that only 1 species remained (sea purslane).


Our second location was on a small near by island called Gun Cay. At this site, we saw a much different habitat dominated by low-lying native plants like inkberry, spider lilies, railroad vine, and buttonwood with a few Australian pines having established themselves in small numbers on the fringe. We followed the same exact procedure we used at our first study site. Here, the average height of the Australian pines measured trees was 31.82 feet, with an estimated 25 trees in our study site. The average canopy cover for trees sampled at this site was 59.35%. With less pines in the area, we observed that both the amount of native plants and diversity increased. In this location, we found 3 different species of native plants (sea purslane, buttonwood, black mangrove) with the native vegetation making up 74.16% of the ground cover sampled.

Although you can easily observe that the presence of Australian pine has a negative impact on native plant species, the data we collected doesn't completely support this statement. There were numerous variables that could have had an effect on the outcome of our data. For example, East Wells had previously had a fire, which killed the majority of the Australian pines in the area, leading to there being a greater amount of canopy cover at the Gun Cay study site because all the trees at East Wells had lost their needles. So even though the Australian pine population at East Wells was far more established and had a greater density of trees, our data showed a lesser canopy cover due to their bare branches. This fact caused the data to appear a little misleading because you would expect a more established population with great density of trees in an area with few remaining native plants to have a high percentage of canopy cover. If we were to replicate or expand on this study in the future we would include more study sites and one that had not been effected by fire.

In the end I believe that the results of our data probably created more questions than it produced answers. Was it the fire that came through East Wells what wiped out all the low-lying native vegetation in the area or was it the established pine population that was blocking the sunlight these plants needed? We also observed that there was a thick layer of pine needles covering the ground in East Wells, what impact does this layer have on native vegetation? Is there a chance that a layer of decomposing pine needles can change the chemistry of the soil to a level that native plants cannot tolerate? Our first location at East Wells was further from the water than our second location at Gun Cay is it possible that the Australian pines act as weed withdrawing valuable water from the ground water from the ground and not allowing the native vegetation to receive enough for their survival - particularly in areas further away from a permanent water source? Whatever the reason may be, there are still many questions that need to be answered before we can figure out what exactly causes Australian pines to outcompete the native vegetation of Bimini. Questions like these need to be answered before strategies can be established to eradicate this native species and restore these area to their native ecosystems.

By: Emilse, John, and Valerie