The effect of overstory composition on understory woody regeneration and species richness in 7-year-old plantations in Costa Rica

Regeneration under tropical plantations has been suggested as a route to facilitate the restoration of natural forests on degraded deforested lands in the tropics. We tested the hypothesis that 7-year-old tree plantations would have greater abundance and species richness of woody colonizers compared to abandoned pastures, but that the response may differ among plantation tree species. Species accumulation curves were constructed for each of seven plantation trees and abandoned pasture. Vochysia guatemalensis and V. ferruginea had higher rates of woody species accumulation in the understory than the other plantations species or the abandoned pasture. When considered by size class of the regeneration, Pentaclethra macroloba plantations had a higher species richness in the 30-200 cm-tall size class compared to the abandoned pastures, and Pines tecunumanii and Vochysia guatemalensis had greater species richness of stems >200 cm tall compared to the abandoned pasture. Composition of the regeneration was dominated by shrubs particularly Conostegia subcrustulata. Nevertheless the Vochysia spp. seemed to favor the presence of a greater diversity of tree species in their understory than the other plantation species. The facilitation of understory development and tree recruitment into the Vochysia plantations may be attributed to suppression of grasses and ferns together with a growth form that attracts seed dispersers. Thus with some plantation species there seems to be a true potential to facilitate a more rapid restoration of a forest community than would occur naturally.