Earthworm populations in a traditional village landscape in Central Himalaya, India

Abstract

Scientific knowledge of belowground biodiversity in the Himalaya, a biodiversity hotspot, is scarce. The aim of this study was to investigate density and biomass of earthworm populations and soil properties (texture, bulk density, organic C, total N and pH) in the full range of land use types viz., moderately degraded natural forests (MDNF), highly degraded natural forests (HDNF), rehabilitated forest land (RFL), traditional pure crop system (TPCS), traditional agroforestry system (TAS), abandoned agricultural land (AAL) and rehabilitated agricultural land (RAL) in a village landscape in Central Himalayan region of India. Of the 8 species present in the landscape, Amynthas alexandri and Metaphire anomala were the most widely distributed taxa, with the former absent only in RAL and the latter only in HDNF, while Bimastos parvus and Perionyx excavatus were confined to MDNF. TPCS and TAFS harboured the same species. AAL had only one (endogeics) and RAL all the three functional groups (endogeics, epigeics and anecics). All species except B. parvus showed a strong effect of season on population size, with the highest abundance and biomass values observed during rainy season. Only D. nepalensis and M. birmanica were a little bit abundant during dry season in TAFS. In the peak month of September, total density showed a trend of TAFS>TPCS>MDNF>RAL>AAL>RFL>HDNF (147, 132, 63, 27, 14, 8 and 5 individuals m−2, respectively) and biomass of TAFS>TPCS>MDNF>RFL>RAL>AAL>HDNF (266, 199, 51, 24, 21, 16 and 11gm−2, respectively). The study shows that (i) a change from TPCS to TAFS follows a substantial increase in earthworm density/biomass but not in species richness, (ii) TPCS/TAFS and MDNF host equal number of species but different species composition, with the former having much larger abundance than the latter, (iii) conversion of TPCS to AAL and of MDNF to HDNF cause drastic reduction in species richness and soil organic carbon (SOC), (iv) rehabilitation (change from AAL to RAL and HDNF to RFL) only partly recuperates SOC and earthworm fauna over a period of 20 years, (v) native species fail to survive in highly perturbed environment in HDNF and also in recuperating RFL but coexist with exotics in all other land use types, (vi) SOC explained around 60% of the variation in total density/biomass and (vii) heterogeneous landscapes with agriculture-forest mixed land uses are likely to support greater species richness than homogeneous agriculture/forest ones. Huge variability in land use histories, management practices and biophysical conditions warrant more research on spatio-temporal dynamics of earthworm communities and the linkages between belowground biodiversity, aboveground biodiversity and ecosystem functions.