Native tree survivorship and growth rates in mixed species plots: Neotropical timber plantations can promote associated biodiversity
Forests have been converted at an alarming rate in tropical and subtropical regions, and tree plantations are replacing both primary and secondary forests. Unfortunately, tree plantations are typically monocultures of non-native species with understories maintained devoid of all other plants. More data on growth rates of native timber species and potential associated biodiversity are needed if native species are to be utilized effectively in diverse plantation systems. This study analyzed survivorship and growth rates of native tree species and associated plant diversity colonizing mixed tree plantations in a lowland wet forest in Costa Rica. Seven native species were planted in abandoned pasture in two sites. Survival, height, and diameter at breast height (DBH) were periodically monitored in six plots of 49 trees each over 13 years. In addition, understory diversity associated with the plantations was examined. Two parallel transects were run in five of the six plots. Sets of 12 quadrats (0.5 m x 0.5 m) were created within each transect to measure percent cover. Within each plot, 2x20 m transects were used to tally and measure DBH for all stems above 1.0 m. All individual plants in quadrats and transects were identified to species.
Two tree species grew rapidly, achieving mean DBHs greater than 20 cm after 13 years of growth—Cordia bicolor and Terminalia amazonia. T. amazonia is an economically useful species that produces hard, durable wood used for furniture, paneling, and flooring. While C. bicolor is useful only for fence posts, its rapid growth makes it a valuable early successional tree. Moreover individuals of C. bicolor have begun reproducing, thereby attracting frugivores to the plots where it occurs. Associated plant diversity in the plantations was high with 142 species from 57 families colonizing the understory of the plantations in the 400 m2 area sampled. These findings demonstrate that using a mixture of native tree species in a plantation setting can provide trees of timber value, while also allowing for rapid re-establishment of understory diversity. We discuss our findings in the context of a mixed-species tree plantation providing harvestable timber while also supporting biodiversity and ecosystem services.