Effects of Pit and Mound Landscape on Soil Ecosystem Engineers at Local Scales - a Case Study in Hyrcanian Forest

Abstract

Earthworms comprise a major proportion of the total invertebrate biomass in terrestrial ecosystems and they are often called ecosystem engineers. Felling of trees by wind occurs continually in forest ecosystems. Many of trees are uprooted by windthrow, annually. The uprooting of old trees creates multiple microsites (e. g. pit and mound landscape) that are main source for soil heterogeneity. Efforts have been made in this study to determine the impact of pit and mound landscape on earthworm assemblages. Due to, the experimental forest station of Tarbiat Modares University studied that is located in Mazandaran province, northern Iran. For this purpose, twenty hectare areas considered and numbers of thirty four uprooted trees were found. Five microsites were distinguished including mound top, mound wall, pit bottom, pit wall and closed canopy. Soil samples were taken at 0~15 cm, 15~30 cm and 30~45 cm depths from all microsites using core soil sampler with 81 cm 2 cross section. Soil pH, water content, organic carbon, total nitrogen and carbon to nitrogen ratio measured in the laboratory. The earthworms were collected simultaneously with the soil sampling by hand sorting method. As a result, in this study soil characters changes had significantly impact on earthworm abundance at local scales. Earthworm's (epigeic, anecic and endogeic) density and biomass had more amounts in pit bottom whereas, no earthworms found in mound top and wall microsites. Principle Component Analysis (PCA) performed on earthworm population and environmental variables showed that water content and C/N ratio are potential indicators of earthworm abundance change.