Establishment and Soil Characterization of Long-Term Forest Monitoring Plots in the Virgin Islands Biosphere Reserve

Matuszak, John; Craft, Ellen; Knausenberger, Walter

Established 3 permanent study plots on St. John - in the Reef Bay, Fish Bay and Hawksnest Bay watersheds. Gathered data on the more prominent trees (includes a few paragraphs about each species) and on soils (pH, salts, organic matter, sodium, texture, P,K, Ca, Mg, S, Zn, Fe, Cu, Mn). Gives management recommendations. Three permanent study plots have been identified and established on St. John, with the overall long-term objective of monitoring representative components of secondary forest development on a small, steep-sloped, dry-to-moist tropical island. The plots are in representative ecological zones-- upland moist forest (Bordeaux), gallery moist forest (L'Esperance) and dry evergreen woodland (Hawksnest), and are 1.0, 0.5 and 0.5 ha in size, resp. They are situated on watersheds of critical importance to the V.I. National Park: Reef Bay, Fish Bay, and Hawksnest Bay, respectively. The bays are the subject of several long-term marine studies by V.I. Resource Management Cooperative and other research groups. The implementation of vegetation and soil studies on these watersheds will allow specific aspects of the association of land and marine systems on this island to be evaluated for the first time. Pertinent background on events leading to this study are given, as is the rationale for selection of the study areas. Topographic and geological characteristics, and past land-use, of these sites are briefly reviewed. The regenerating forest is an intriguing mixture of native and introduced species. Comparative study of the relative development of these two groups is likely to be most instructive, and of high relevance to other islands, especially in the Neotropics. Of the twelve species of trees most abundant in one or more of the three plots, eight are discussed briefly in their biological, historical and cultural contexts: Acacia muricata, Andira inermis, Ardisia obovata, Byrsonima coriacea, Guapira fraqrans, Inqa fagifolia, Pimenta racemosa, and Tabebuia heterophylla. Soil was sampled at three depths from 33 sites immediately outside the perimeter of the three study plots. The samples were analyzed for pH, soluble salts, organic matter, sodium content, texture, five macronutrients (exchangeable P, K, Ca, Mg, S), and four micronutrients (exchangeable Zn, Fe, Cu, Mn). Nitrogen was not analyzed. The average pH ranged from 5.71 at Bordeaux, to 7.12 at Hawksnest. Percent organic matter was rather high, normal in a forest environment, but the Hawksnest plot was consistently lowest. Most of the nutrients were in the low-to-medium range, with the exception of iron, which was high to very high at the Bordeaux plot. The latter is consistent with the results of a geochemical survey of St. John by Tucker et al. (1985). Some differential in nutrient levels is apparent within and among the study areas, and these could have an effect on plant distribution and growth, but detailed analysis of this is beyond the scope of the present report. Representative specific recommendations arising from this study are offered, concerning terrestrial plant development, soils and nutrient relationships, as they relate to management considerations and information and education needs in the Virgin Islands.