Long-term Change in Plant & Animal Communities in the Bahamas

Figure 1. Nancy Albury and Dr. David Steadman at a blue hole dive site, Sawmill Sink on Abaco, examining the fossilized skull of a Cuban crocodile, recovered by diver Brian Kakuk (not shown). This species of crocodile is now extinct throughout the Bahamas.

In the Bahamas, there are extremely well preserved plant and animal fossils
in blue holes, providing an unparalleled record of environmental change –
blue holes have been called a window to the past. Findings of tortoise and
Cuban crocodile fossils from Abaco blue holes have even been featured in
National Geographic Magazine
. We  — David Steadman (University of Florida),
Patricia Fall and I (Arizona State University) — have recently received support
from the US National Science Foundation to build on these fossil findings
by studying long-term change in plant land animal communities on Eleuthera
and Abaco.

We’re especially interested in how Bahamian flora and fauna respond to long-term fluctuations in the environment and the impacts of Amerindians about 1000 years ago. There are a couple of questions we’re using to guide our research. The first is: what were the relative influences of climate change vs. human impact on ancient Bahamian landscapes? By using radiocarbon dating, we can begin to understand the changes in Bahamian plants and animals that occurred both before and after human arrival on the islands. Since pine produces abundant pollen carried great distances by wind, pollen percentages as low as we have found at Sawmill Sink (10-30%) suggest that little Pineyard habitat (Pinus caribaea Woodland; PW) existed on Abaco in the Late Holocene (ca. 4000 to 2000 BP). Human-set fires in the last millennium may have changed the vegetation near Sawmill Sink from coppice (subtropical dry evergreen forest) to the PW that now dominates Abaco (Figure 2 shows examples of the two terrestrial forest habitats).

The second question is: what are the long-term impacts of modern land use on terrestrial plants and animals? By studying modern Bahamian plant and animal communities, we will be able to improve our understanding of the influence of both prehistoric and historic land use.

Figure 2. Left column: Pine Woodland (PW), right column: Coppice. Top row: hemispherical photo, middle row: photo. Bottom row: Google Earth™ image.

Many of the same trees dominate both modern Coppice on Abaco and Late Holocene
pollen record from Sawmill Sink (Table 1).

Table 1. Average relative basal area (RBA, %) for species with RBA > 1% in 10 preliminary Coppice plots (10-m radius) on Abaco, The Bahamas. 34 species recorded in total. *, represented in pollen data, at least at the family level. Sapo = Sapotaceae.

There are major differences in the resident (Fig. 3) and migrant bird communities in
PW vs. Coppice on Abaco (Table 2). Only 14 of 25 resident species were found in both
habitats. The 3 most common residents in PW were not recorded in Coppice, and the
3 most common residents in Coppice were rare in PW. Coppice sustains more migrant
species than PW.

Table 2. Average individuals per point (only habitat indicator species are shown), Abaco, Bahamas, 11-16 Dec 2007, 13-18 Jan 2009. For each habitat type, N = 44 points (22 per year). Cop = Coppice indicator species; PW = Pine woodland indicator species. Nine other migratory species, and 14 other resident species, were recorded but are not listed because they do not specialize on either PW or Coppice. Their values are, nevertheless, included in the totals.

 

While the absence of pines on Eleuthera and southeastward through the Bahamas may
be natural, the dominance of PW on the four islands with pines may signal a more
substantial cultural disturbance upon colonization in the north compared to more
modest disturbance on the more southern islands. We expect to see the extinct animals
associated with Coppice on both Abaco and Eleuthera, followed by the disappearance
of extinct animals associated with a charcoal spike and a shift to pine woodland on
Abaco. We also predict that the vertebrate fauna will have a strong component of extinct
species before human arrival, with these species dying out in the subsequent centuries.
Even on PW-dominated Abaco, we predict that the landscape had a greater component
of Coppice before human arrival.

Working with The National Museum of the Bahamas, The Bahamas National Trust,
Friends of the Environment, Bahamas Caves Research Foundation and other groups in
the Bahamas will allow us to use specimens and artifacts collected from blue holes, our
window to the past, to address these fascinating questions about long-term
environmental change in the Bahamas.

By | 2017-12-01T14:05:04-05:00 May 23rd, 2012|Categories: Birds, Blue Holes, Fossils, Geology, Global change, Plants|0 Comments

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