Cox, Anne Cheney.

Sixty-two coastal and inland tree islands (hammocks) in Martin and Palm Beach Counties were mapped. Species composition was determined for 36 sites and used to test several hypotheses. The hypothesis was tested and supported that the percentage of tropical species inhabiting a tree island increases on north to south and west to east gradients. A linear regression was run to determine patterns in percent composition of tropical species and whether low hammocks were separable from high hammocks. Data suggested that a range from 70 to 80 percent tropical species composition might be used to define "tropical" hammocks. Since hammocks in southern Florida are considered habitat islands, the MacArthur and Wilson concept was tested. An obtained slope (z value) of 0.18 compares well with the slope of 0.17 predicted by the MacArthur and Wilson model. A cluster analysis showed similarities of 36 sites based on 83 tree and shrub species present.