Earthworm abundance and species composition in abandoned tropical croplands: Comparisons of tree plantations and secondary forests

We compared patterns of earthworm abundance and species composition in tree plantations and secondary forests of Puerto Rico. Tree plantations included pine (Pinus caribaea Morelet) and mahogany (Swietenia macrophylla King) established in the 1930s; 1960s; and 1970s; secondary forests were naturally regenerated in areas adjacent to these plantations. We found that (1) earthworm density and fresh weight in the secondary forests were twice those in either of the tree plantations, and did not differ between the plantations, and (2) the exotic earthworm species, Pontoscolex corethrurus Muller, dominated both plantations and the secondary forests, but native earthworm species, Pontoscolex spiralis Borges & Moreno, Estherella montana Gates, and E. gatesi Borges & Moreno, occurred only the secondary forests. Our results suggest that naturally-regenerated secondary forests are preferable to pine and mahogany plantations for maintaining a high level of earthworm density, fresh weight, and native species.