Spatial Distribution of Earthworms in an East Texas Forest Ecosystem

Abstract

Earthworms were collected and identified in different ecological habitats of the Stephen F. Austin Experimental Forest (SFAEF) in the Piney Woods Ecoregion (PWE) of Texas. Earthworm spatial distribution data were collected over four distinct ecological habitats with a range of soil conditions and vegetative cover. A total of 128 sampling plots were surveyed in two different, broadly defined locations (mesic slope=68 plots, dry-mesic upland=60 plots). Using multivariate classification/ordination (TWINSPAN) and detrended correspondence analysis (DCA) of overstory vegetation data, these two locations were further divided into four distinct habitats: dry-mesic mixed upland, transitional zone, mesic slope and wet forested seeps. By using TWINSPAN and principal component analysis (PCA), it was found that earthworm species assemblages and understory vegetation corresponded to these discrete ecological habitats. ArcGIS10 was then used to create spatial distribution maps of earthworm species throughout these delineated ecological habitats in the SFAEF. Six earthworm species from the native North American genus Diplocardia were collected at SFAEF: D. caroliniana Eisen (1899), D. eiseni Michaelsen (1894), D. komareki Gates (1977); D. macdowelli Murchie (1963), D. mississippiensis Smith (1924) and D. ornata Gates (1943). Two earthworm species from the native North American genus Bimastos were collected: B. heimburgeri Smith 1928 and B. longicinctus Smith and Gittins 1915. The collection of B. longicinctus is a new state record for Texas. Amynthas corticis Kinberg (1867) specimens were collected, which represent a non-native genus from Southeast Asia. Ocnerodrilidae, a megadrile family first described by Beddard in 1891, were also collected likely representing non-native species originating from intertropical America and Africa (Christoffersen, 2008).