TROPICAL DRY FORESTS OF ST-LUCIA, WEST-INDIES - VEGETATION AND SOIL PROPERTIES

The tropical dry forest life zone of St. Lucia is largely covered by s crub forest characterized by a short canopy and a large number of smal l-diameter trees. However, it is unclear whether these short-stature f orests result from edaphic properties that limit the development of ta ller-stature dry forest or result from the repeated harvest of wood. T o investigate the influence of edaphic properties on forest compositio n and structure, we sampled 21 stands within the dry forest life zone of St. Lucia. Mean canopy height in the scrub forest was 4 m and stand s contained an average of 39,407 stems ha(-1); 96 percent of those ste ms were less than or equal to 5 cm in diameter. Mean basal area in the scrub forest (stems greater than or equal to 1.0 cm DBH) was 15 m(2) ha(-1), 62 percent of which consisted of stems less than or equal to 5 cm in diameter Guettarda scabra (Rubiaceae) and Croton spp. (Euphorbi aceae) were the most common species. Soil organic C averaged 3.2 perce nt, potential net N mineralization was 1.49 mu g N g(-1) d(-1), and po tential net nitrification was 1.61 mu g NO3--N g(-1) d(-1). Concentrat ions of available P ranged from 1 to 3 mg kg(-1). We found no relation ship between vegetation and soil properties in the scrub forest of St. Lucia. Moreover, most soil properties in the short-stature scrub fore st did not significantly differ from those of relatively undisturbed t ropical dry forest in our study area, even though overstory compositio n and structure differed dramatically. Rates of net N mineralization i n the scrub forest were 57 percent of those in a relatively undisturbe d dry forest; chat difference was significant. The similarity of soil properties between short-stature scrub forest and relatively undisturb ed dry forest suggest that repeated disturbance, rather than edaphic p roperties, is a major influence on forest composition and structure wi thin the dry forest zone of St. Lucia.