Original articleLand use change affects earthworm communities in Eastern Maryland, USA
Introduction
It has been estimated that prior to European settlement 95% of Maryland was covered with forests [2]. In the Chesapeake Bay region land clearing peaked in the late 1800s, when over 80% of the land was used for agriculture. By the 20th century much of this land has grown back to forest [27]. Today urban and suburban development is the major reason for loss of the remaining forests and agricultural land.
Earthworm invasion in North America has become a major ecological, conservation and management issue [4], [14], [16], [23]. Converting forests into agricultural fields has facilitated exotic earthworm establishment and further dispersion. The steps of earthworm colonization in forests and disturbed sites have been demonstrated in several studies [19]. Much less is known of the reverse process, i.e. how earthworm assemblages change when abandoned disturbed sites, such as agricultural fields are left for forest regrowth [20]. The objective of our study was to compare species composition and abundance in physically adjacent forest stands of various stages of old field succession. We expected high species richness and abundance in the successional stands, because of the age of these forests is closer to the initial disturbance. However, it is not known whether these assemblages can maintain high abundances over time, as the forests mature.
Section snippets
Study site
The Smithsonian Environmental Research Center (SERC hereafter) lies in the Rhode River estuary along the western shore of Maryland. This 2886-hectare watershed is 62% forest, 23% croplands, 12% pasture, and 3% freshwater swamp. The watershed is underlain by relatively impermeable clay layer. Soils at all study sites are fine sandy loams of the Collington–Monmouth series that have formed on sedimentary soils from the Pleistocene Talbot formation [8], [28]. The 160-year average rainfall is 1080
Results
The 1651 specimens collected belonged to 12 species (Table 1). With the exception of the native Diplocardia caroliniana (Acanthodrilidae) all species belong to the family Lumbricidae. Bimastos palustris and Eisenoides loennbergi are native North American lumbricids, the rest are of European origin. Surprisingly, the common anecic Lumbricus terrestris has not been found at SERC. However, L. friendi, recently recorded for the first time in North America [9], proved to be fairly common in the
Discussion
Non-native earthworms in North America have received a lot of attention both in the scientific literature and in the media (e.g. [4], [14], [16]). The concern is that exotic earthworms modify forest floor structure, soil characteristics and element cycling [3], [15], which results in change in other soil biota and loss of native rare understory plant species [12], [13], [19].
Most of the experiments and observations are reported from the Northern-Northeastern region that has lacked native
Acknowledgements
This study was partially supported by the National Science Foundation (DEB-9714835, DEB-0423476) and the Hungarian Science Research Found (OTKA No. T43508, OTKA T42745). We thank Anson Hines for granting permission to work on the SERC property, Dennis Whigham for the vegetation maps, Melissa McCormick for many useful discussions, and Peter Sólymos for helping with the statistical analysis. Two anonymous reviewers made helpful comments on an earlier version of the manuscript. Kim Townsend helped
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