Unexpected earthworm effects on forest understory plants

Andrea Dávalos,Jordan Stark,Bernd Blossey,Victoria Nuzzo

doi:10.1186/1472-6785-13-48

Abstract

BackgroundIntroduced earthworms are widespread in forests of North America creating significant negative impacts on forest understory communities. However, much of the reported evidence for negative earthworm effects comes from field investigations either comparing invaded and non-invaded forests or across invasion fronts. While important, such work is rarely able to capture the true effect of earthworms on individual plant species because most forests in North America simultaneously face multiple stressors which may confound earthworm impacts.We used a mesocosm experiment to isolate effects of the anecic introduced earthworm, Lumbricus terrestris L. on seedlings of 14 native plant species representing different life form groups (perennial herb, graminoid, and tree).ResultsEarthworm presence did not affect survival, fertility or biomass of any of the seedling plant species tested over a 17-week period. However, L. terrestris presence significantly decreased growth of two sedges (Carex retroflexa Muhl. ex Willd. and Carex radiata (Wahlenb.) Small) by decreasing the number of culms.ConclusionsOur mesocosm results with seedlings contrast with field reports indicating extensive and significant negative effects of introduced earthworms on many mature native forbs, and positive effects on sedges. We suggest that earthworm impacts are context- and age-specific and that generalizations about their impacts are potentially misleading without considering and manipulating other associated factors.

Highlights

Introduced earthworms are widespread in forests of North America creating significant negative impacts on forest understory communities
We fitted a Generalized Linear Model (GLM) with binomial errors to evaluate the effect of earthworm treatment, plant life form and plant species on plant survival
We evaluated earthworm effects on the probability of flowering of A. gryposepala and A. hyemalis with a second GLM

Summary

Introduction

Introduced earthworms are widespread in forests of North America creating significant negative impacts on forest understory communities. While important, such work is rarely able to capture the true effect of earthworms on individual plant species because most forests in North America simultaneously face multiple stressors which may confound earthworm impacts. The spread of non-native earthworms into previously earthworm-free temperate hardwood forests in North America can have significant ecosystem effects [1,2]. Earthworm relative abundance and their associated impacts are affected by land use history and grazing regimes [17], facilitation between earthworms and non-native plant species [7], and alterations of predator–prey interactions [6,18]. Earthworms and abundant white-tailed deer (Odocoileus virginiana Zimmermann) in North America may interact and affect plants in multiple yet poorly understood ways. Earthworms benefit from high deer abundance by utilizing fecal pellets as a food resource [19], and earthworm invasion followed by the demise of vulnerable plants may increase deer feeding pressure on remaining plants further reducing forest plant diversity [1]

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