Restoration of a Sri Lankan rainforest: using Caribbean pine Pinus caribaea as a nurse for establishing late-successional tree species.
In the moist tropics, studies have demonstrated poor seedling establishment of late-successional trees on lands cleared of forest. This study examined the potential for establishing late-successional tree species that dominate the canopy of rain forest by planting within and adjacent to experimental openings that were created within a Pinus caribaea plantation. Use of the method was tested with 5 canopy tree species (Dipterocarpus zeylanicus, Mesua ferrea, Shorea disticha, S. megistophylla and S. trapezifolia) of tropical forest in south-western Sri Lanka. Seedlings were monitored for 2 yr within treatments that removed either 3 rows or 1 row of Pinus canopy, a canopy edge treatment and a control that left the canopy intact. The greatest growth and dry mass for all species were in the canopy removal treatments. In particular, S. trapezifolia and S. disticha exhibited the greatest height growth in these treatments. In the 3-row canopy removal treatment, M. ferrea had a significantly lower dry mass than the other species. Differences were shown in the number and area of leaves among species. Shorea trapezifolia, and to a lesser degree S. disticha, increased area by increasing leaf production. Dipterocarpus zeylanicus, and to a lesser degree M. ferrea, increased area by increasing the size of individual leaves. Guidelines based on results from this study recommend that species grow best when seedlings are planted within openings created by the removal of 3 rows of Pinus canopy. Where planting without canopy removal is required, S. disticha or S. megistophylla should be selected because of their greater shade and drought tolerance. This experiment demonstrated that Pinus can be used as a nurse for facilitating the establishment of site-sensitive tropical forest tree species that are late-successional. In particular, results have application for similar mixed dipterocarp forest types in SE Asia.