Dominance of native earthworms in secondary tropical forests derived from slash-and-burn Mayan agricultural practices (Yucatán, Mexico)

Abstract

In order to assess earthworm communities influenced by successional changes in tropical subdeciduous forest (TSF), we studied several secondary forests developed after annual crops in southern Yucatan (Mexico). All these secondary TSF were derived from slash-and-burn (S&B) Mayan shifting agricultural practices. Accordingly, four repetitions of four stages in the S&B shifting system were selected: currently cultivated annual maize crops, three-year-old fallow, and 20- to 30-year-old and 50-year-old secondary forests. Earthworm communities were characterized according to richness, abundance, and biomass values; some soil-related variables were also determined, both environmental (litter, moisture, and temperature) and physicochemical (texture, Cation exchange capacity-CEC, P, N, C). C and N content and CEC were lower in annual crops than in fallow and forests. Except for soil temperature (slightly lower in forests stages) and clay and sand content (respectively lower and higher in late stages), the other edaphic (pH, P content) and environmental variables (litter and soil moisture content) did not vary among successional stages. Five species of earthworms were found, one exotic (Dichogaster affinis) and four native (Balanteodrilus pearsei, Diplotrema oxcutzcabensis, Mayadrilus calakmulensis, and an unidentified ocnerodrilid). A higher number of species (4) was found in annual crops, whereas late successional stages contained only two species; conversely, higher values of abundance and biomass were found in 50-year-old forests than in annual maize crops. The native B. pearsei dominated all successional stages, with relative values of abundance and biomass over 80% in fallow and forested stages, reaching up to 99% in 50-year-old forests. The single exotic species was limited to annual crops with relatively low abundance and biomass values. We discuss the reasons for the prevalence of the native B. pearsei and the absence of exotic species in successional stages, especially regarding the kind of soils characteristic of the Yucatán peninsula, and the persistence of ancient Mayan agricultural practices.