Silvicultural and economic aspects of pure and mixed native tree species plantations on degraded pasturelands in humid Costa Rica

Reforestation of degraded land in tropical regions provides one means of restoring ecosystems and improving rural livelihoods. Most plantations in humid tropical regions are established in pure plots, including few species of high commercial value, generally exotics. The present study compares growth and economic viability of 15-16 year-old trees of native species in pure and mixed plantations on degraded pasturelands at La Selva Biological Station, Costa Rica. The species with the best growth were Vochysia guatemalensis, Virola koschnyi, Jacaranda copaia, Terminalia amazonia, and Hieronyma alchorneoides. The mixed plantations performed better than pure plantations for all growth variables considered, including height, diameter at breast height, volume, and aboveground biomass. Mixed plantations outperformed pure plantations economically, with Net Present Value (NPV) of $1,124 to $8,155/ha and Internal Rate of Return (IRR) of 7.7-15.6% depending on the species mixture. The most profitable pure plantations were those of Vochysia guatemalensis, with NPV and IRR of $6,035/ha and 14.3%, respectively; Hieronyma alchorneoides ($2,654 and 10.8%); and Virola koschnyi ($1,906/ha and 9.22%). These are the estimated benefits that would be accrued at harvest. These projections are realistic since the decision to harvest is generally mandated not just by profit maximization but by economic necessity, thus many small- to medium-scale farmers in Costa Rica harvest plantations prior to the completion of the rotation length. Mixed plantation may be the preferred system for reforestation with native species designed for timber production or carbon sequestration because this system is more economically viable and productive than pure plantations.