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This study documents the status of forest vegetation in the karst region of Los Haitises National Park, Dominican Republic, following the abandonment of pastures (≤5 years), young (≤5 years) `conucos' (mixed plantings), old (7–30 years) conucos, and cacao plantations (>25 years). We compared these sites to vegetation characteristics of patches of forest in karst valleys (`old forest'–too old to know their exact land use) and on mogote tops with no recent history of human disturbance. The youngest sites date to when squatters were removed from Los Haitises National Park. Forest structure (density, basal area, and species richness of woody plants ≥1 cm DBH) were all significantly affected by land use. Density was highest in intermediate-aged valley sites (old conucos) and mogotetops, while both basal area and species richness tended to increase with age of abandonment. Although cacao plantations had been abandoned for more than 25 years the species diversity was low, due to continued regeneration of this persistent crop. Abandoned pastures had the greatest nonwoody biomass and were dominated by the fern Nephrolepis multiflorawhich had completely replaced pasture grasses. An ordination of the woody plant communities separated the mogotetops from valleys, emphasizing the strong control that topography has on the forest community in moist and wet tropical forests on karst substrates. Valley sites were arranged in the ordination in order of their age, suggesting a successional sequence converging on the composition of the `old forest' sites.

We have demonstrated specific adenosine 5',5‴ -P₁,P₄-tetraphosphate (Ap₄A) receptors at heart cell surfaces (1-3). Optimal Ap₄A binding requires receptor activation (2, 4). Other investigators have demonstrated that Ap₅A and Ap₆A act as vasopressors (5). We now compare the binding of Ap₄A, Ap₅A and Ap₆A on heart membranes to determine if all three ligands bind to the same receptor and their relative avidities. Anti-Ap₄A receptor antibodies inhibit the binding of all three ligands. SDS-PAGE analysis of Ap₄A, Ap₅A and Ap₆A cross-linked to membranes reveals that all three are attached to a 30 kDa peptide. The specific activity for binding to unactivated membranes is similar for all three ligands. However, after receptor activation there is a 3.4× increase in Ap₄A binding and a 32.5× decrease in the KD; values remain unchanged for Ap₅A and Ap₆A. These data indicate that Ap₄A, Ap₅A and Ap₆A bind to the same receptor on cardiac membranes but receptor activation enhances only Ap₄A binding.Copyright 1994, 1999 Academic Press, Inc.