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Guayanilla Windfarm EIS: species-area relationships  

The proposal by WindMar RE to build a windfarm at Punta Verraco, Cerro Toro and Punta Ventanas in southwestern Puerto Rico has generated controversy (see my first post on the issue) on a number of issues. One of the things that bothers me most is the sloppy Environmental Impact Statement. I have not read the whole thing, but the biological aspects are disturbingly bad.

One of the most fundamental issues in ecology is the species-area curve. Species richness increases with area (but not linearly). Larger areas have more species. On a certain level this in intuitively obvious – the smallest possible area has one individual, so it can only have one species. If you expand your sample to include two individuals, you may find that the second individual belongs to the same species, or you may find another species. If every new individual encountered was a member of a new species, you would have a line with a slope = 1. In reality though, you are almost certain to encounter more than one individual of at least some of your species, so your curve will flatten a little bit. (What I am describing is a species-individual curve rather than a species-area curve, but similat rules apply for area.) One of the fundamental points that comes from this is that larger areas will contain more species. This is one of the most basic relationships in ecology. Anyone who has any background in ecology knows this. Unfortunately, this seems to have slipped the mind of the authors of the Habitat Conservation Plan (p. 27):

So far, botanists have recorded nearly 170 species of vascular plants at the WindMar site (see Appendix II), a diversity far below the over 700 species recorded in the Guánica State Forest. … This confirms hat the dry forest plant community on the WindMar site is poor and has been severely impacted. A management plan to help these forests recuperate is clearly in order.

Guánica Forest occupies about 4000 ha. The site in question occupies 290 ha. No one would expect the site to have anywhere near the number of species than Guánica Forest has. However, if you examine the species list (p. 13) you will see that it lists 168 species from Punta Verraco, which accounts for only 43% of the site (125 ha; Habitat Conservation Plan, p. 24). In addition, the authors of the report cite no sources for their figure of “over 700 species” recorded for Guánica Forest – the most recent source I am aware of lists a little over 650 species. Regardless, what this accounts for 24-26% of the species recorded for Guánica Forest in about 3% of the area. Add to that the fact that the species list for Guánica Forest includes habitats not represented in the survey, and you end up coming to the conclusion that species diversity of this site is very high.

When the authors of the report get the most basic biology so badly wrong, you tend to lose confidence in what they have to say rather rapidly.


24 July 2007

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