Restoring abandoned pasture land with native tree species in Costa Rica: Effects of exotic grass competition and light

Background

Understanding the early establishment requirements and performance of tropical tree seedlings is essential to ensuring the success of restoration plantings. This study characterizes growth and light requirements of six common neotropical tree species: Pseudosamanea guachapele (Fabaceae), Tabebuia impetiginosa (Bignoniaceae), Ceiba pentandra (Bombacaceae), Pachira quinata (Bombacaceae), Dalbergia retusa (Fabaceae), and Tabebuia rosea (Bignoniaceae).

Research goals & methods

Field studies were conducted in the pastures of the Santa Ana Conservation Center in Costa Rica under contrasting light environments and grass competition. Two differing grass competition sites were selected, one dominated by a tall grass, Hyparrhenia rufa and another dominated by a short grass, Cynodon mlenfluensis. Three light treatments were created (2, 37 and 100% light) using either neutral shade cloth (2 and 37%) or no shade cloth (100%). Growth characteristics and biomass partitioning of the seedlings were measured. Species differed in their relative growth rates (RGRs). The light × species interaction was significant at both sites. While all species had similar performance under 100% light on both short grass and tall grass sites, species growth differences were evident under 37 and 2% light levels. The general trend was to increase root mass ratio and decrease leaf mass ratio with increasing levels of light.

Conclusions & takeaways

The authors recommend using all these species in direct and moderate light conditions as an initial step for reforesting abandoned pasture lands. Incorporating all species will create a more heterogeneous environment. Choosing fast-growing light demanding species that can tolerate grass competition may help ensure success in the early stage of restoration.