Natural establishment of indigenous trees under planted nuclei: A study from a clear-felled pine plantation in an afrotropical rain forest

Applied nucleation has been proposed as a cost-effective reforestation alternative to large-scale re-planting or establishing plantations with exotic tree species. We tested applied nucleation in a regenerating clear-cut pine plantation in Kibale National Park, Uganda, where natural succession had been slow. We planted Neoboutonia macrocalyx, a relatively common indigenous pioneer tree species with animal dispersed seeds and a wide crown, in the pine plantation clear-cuts as seeds and transplanted seedlings. After six years of monitoring the growth of the nucleus trees we identified all naturally recruited seedlings under the nuclei and adjacent control sites without planted nuclei. We monitored the growth and turnover of the recruited seedlings for one year and examined the ground vegetation structure under the nuclei and control sites. We found that the N. macrocalyx nucleus trees had survived equally well if planted as seeds or transplanted seedlings and had attained heights up to ten meters tall. Understory vegetation structure under the established nuclei was less dense (P = 0.001) and shorter (P = 0.039) compared to control sites. We also found that natural recruitment of indigenous tree species under the nuclei was higher compared to control sites. The seedling density under the nuclei was significantly higher (P = 0.035), and there was a significant difference in the composition of seedling communities (P = 0.0001) with a larger number of different tree species found under the nuclei. We found that a viable seedling community had been established with a good potential to take over when planted nucleus trees eventually die. Our results show that planting nucleus trees can increase recruitment of indigenous tree species in locations where natural succession is otherwise slow. (C) 2015 Elsevier B.V. All rights reserved.