Earthworms in abandoned tropical pastures



Short name: 


Data set ID: 



Plant community succession alters the quantity and chemistry of organic inputs to soils. These differences in organic input may trigger changes in soil fertility and faunal activity. We examined earthworm density and community structure along a successional sequence of plant communities in abandoned tropical pastures in Puerto Rico. The chronological sequence of these plant communities were pasture, grass-vine-fern, shrub-small tree, and forest. Earthworm density was the highest in pasture (831 worms/m2 in top 0.25 m soil), decreased as secondary succession proceeded, and reached the lowest (32 worms/m2) in the forest. Whereas only soil feeding Pontoscolex corethrurus was present in the pasture and grass-vine-fern communities, both soil and litter feeding worm species were found in the shrub-small tree and forest communities. Ground litter biomass had a negative correlation with earthworm density. Soil water content differed slightly among the successional communities, but were unlikely to play an important role in triggering differences in worm density among these abandoned lands. Soil pH values did not differed along the successional changes. These results suggest that decrease in earthworm density and increase in worm community diversity during secondary succession may result from changes in the quantity and chemistry of organic inputs, rather than in soil properties. We conclude that successional development from grass-dominated pastures to woody species-dominated forests reduces earthworm density and diversifies worm community structure in humid tropical soils.

Date Range: 
1993-06-21 00:00:00 to 1993-07-28 00:00:00





Using air photos taken in 1936, 1951, 1964, 1971, 1977, 1983, 1988, 1991 and 1993, we were able to locate four sites adjacent to each other on the same hill slope north of the Rio Sabana. Three sites were deforested and converted to pastures prior to 1936, two of which had subsequently been abandoned by 1971 and 1988, and one has been maintained as pasture. The fourth site has been forest since 1936. The site abandoned in 1971 has developed into a shrub-small tree community (Aide et al., 1995) dominated by species in Melastomataceae (Miconia prasina, M. impetiolarias, M. racemosa) and Rubiaceae (Palicourea riparia, Psychotria brachiata). The more recently abandoned site has developed into a grass-vine-fern community. Soils in all the study sites are Oxisols, belonging to the Zarzal series with high clay content. Earthworms were sampled between June 21 and July 28, 1993. Three 0.25 m2 (pasture and grass-vine-fern communities) or 0.5 m2 (shrub-small tree and forest communities) plots were located 15 m apart in each site along the slope. Ground litter (leaves and twigs < 2 mm) were collected in each plot and stored in plastic bags. Soils in the upper 250 mm were then removed onto a cloth sheet. Earthworms were hand- sorted and stored in plastic bags in a cooler with ice. A soil sample was taken from each plot and placed in a plastic bag for measuring pH and water content. Ground litter biomass was obtained after drying twigs and leaves at 60 C for at least 72 hrs. Fresh weight of earthworms was acquired after the worms were rinsed with water and dried with paper towels on the same day they were collected. Soil moisture content was calculated for each site by oven-drying 15 g of fresh sample at 105 C for 48 hrs. Soil pH was measured using a paste of 1:1 ratio of fresh soil and deionized water. The analyses of variance and Scheffe's multiple range test were employed to examine differences among successional communities. The significance level was set at alpha = 0.10.



Time Period: