The effects of moisture and shade on seed germination and seedling survival in a tropical dry forest in Jamaica
The effects of light and moisture on the early establishment of four canopy tree seedlings were studied from October 1999 to August 2000. The study was undertaken in a primary dry forest in the Hellshire Hills protected area, Jamaica with rainfall for the year totaling 650 mm most of which fell during the 6-month long rainy season. Seeds of Calyptranthes pallens, Eugenia sp., Hypelate trifolia and Metopium brownii were collected 1 month prior to the peak in the rainy season and planted in a nursery constructed within a cleared area of the forest according to a split-plot design which consisted of three blocks each containing three main treatment plots (no shading, partial shading and heavy shading) with each main plot being sub-divided into two sub-plots (regular watering and no watering). Seedling germination was prompt with shading having a more positive significant effect on seed germination than watering. Seedling mortality was high during the dry season particularly after the first month following a significant reduction in rainfall but seedling survival stabilised at the start of the wet season. Seedling survival was lower in un-shaded than shaded plots and in the shaded plots, survival was lower in partially shaded plots than in heavily shaded plots. Water supplement prolonged the survival of all individuals regardless of shading. Seedling size was positively affected by shading with seedlings within the partially shaded plots attaining the highest basal diameter while seedlings in the heavily shaded plots were the tallest. Water supplement also positively affected seedling size. High light levels during the wet period improved seedling growth but significantly increased seedling mortality during the dry season for all species. With respect to seedling response, M. brownii had the highest germination percentage and production but was most sensitive to drought. C. pallens had the highest survival and produced the smallest individuals. However, Eugenia sp. had the highest number of seedlings surviving at the end of the experimental period, and showed the lowest drought sensitivity.