Individual tree species effects on earthworm biomass in a tropical plantation in Panama

The impact that tree plantations have on biodiversity conservation is unclear, therefore, it is of major interest to understand the links between trees and the organisms associated with them. The objective of this study was to examine the effect of individual tropical tree species and neighborhood interactions on earthworm abundance. The study was conducted in Panama using six native tree species: Luehea seemanii, Cordia alliodora, Anacardium excelsum, Hura crepitans, Tabebuia rosea and Cedrela odorata. Trees were grown either in monocultures or in three-and six-species mixtures in 45 x 45 m plots and ranged between 3-4.5 m height at the time of the study. Formalin was used to extract earthworms and hand sorting was used for the top 5 cm of soil. I hypothesized that earthworm biomass depended on the individual tree species. Results showed that the tree species had a significant effect on earthworm fresh biomass (F-5,F-92 = 2.546, p = 0.033). Hura crepitans supported on average the highest earthworm biomass (13.4 g/m(2)). As a second set of analyses I performed an ANOVA to test for the possible tree neighbor effect. It showed that when either C. alliodora or A. excelsum are the neighboring trees, they decrease the earthworm biomass of their neighbor (p = 0.020 and p = 0.050, respectively). A new species of earthworm was discovered at the site: Anteoides n. sp. I failed to find a significant effect of plots (monoculture and mixtures) on earthworm biomass. This study provided evidence to support the hypothesis that some tree species favor earthworm biomass over other species.