Earthworm invasion into previously earthworm-free temperate and boreal forests

Abstract

Earthworms are keystone detritivores that can influence primary producers by changing seedbed conditions, soil characteristics, flow of water, nutrients and carbon, and plant-herbivore interactions. The invasion of European earthworms into previously earthworm-free temperate and boreal forests of North America dominated by Acer, Quercus, Betula, Pinus and Populus has provided ample opportunity to observe how earthworms engineer ecosystems. Impacts vary with soil parent material, land use history, and assemblage of invading earthworm species. Earthworms reduce the thickness of organic layers, increase the bulk density of soils and incorporate litter and humus materials into deeper horizons of the soil profile, thereby affecting the whole soil food web and the above ground plant community. Mixing of organic and mineral materials turns mor into mull humus which significantly changes the distribution and community composition of the soil microflora and seedbed conditions for vascular plants. In some forests earthworm invasion leads to reduced availability and increased leaching of N and P in soil horizons where most fine roots are concentrated. Earthworms can contribute to a forest decline syndrome, and forest herbs in the genera Aralia, Botrychium, Osmorhiza, Trillium, Uvularia, and Viola are reduced in abundance during earthworm invasion. The degree of plant recovery after invasion varies greatly among sites and depends on complex interactions with soil processes and herbivores. These changes are likely to alter competitive relationships among plant species, possibly facilitating invasion of exotic plant species such as Rhamnus cathartica into North American forests, leading to as yet unknown changes in successional trajectory.

Resource Utilization by Native and Invasive Earthworms and Their Effects on Soil Carbon and Nitrogen Dynamics in Puerto Rican Soils

“…Invasive earthworms have caused significant effects on local biota and ecosystem processes (such as nutrient dynamics) in the invaded areas, e.g., European Lumbricids in North America [1][2][3]. Population declines of native earthworms, particularly in remote and non-fragmented forests, have contributed to a result of competitive exclusion by expanding invasive earthworm populations [2,4,5].…”

“…Earthworm invasions have significantly altered nutrient dynamics (e.g., carbon (C) and nitrogen (N)) in invaded soils [1,11,12]. A mixed-species of European Lumbricid earthworm assemblage has been documented to lessen organic layers and relocate leaf litter and humus fragments (C) into the deeper mineral soils, as well as to cause an increase of N loss in the soil adjacent to plant roots in the temperate forests of North America [1].…”

“…A mixed-species of European Lumbricid earthworm assemblage has been documented to lessen organic layers and relocate leaf litter and humus fragments (C) into the deeper mineral soils, as well as to cause an increase of N loss in the soil adjacent to plant roots in the temperate forests of North America [1]. The effects of earthworms on soil C and N dynamics may vary with the feeding strategies of earthworms and composition of earthworm assemblages [13].…”

“…The effects of earthworms on soil C and N dynamics may vary with the feeding strategies of earthworms and composition of earthworm assemblages [13]. For example, epigeic earthworms may have stronger effects on nutrient fluxes between leaf litter layers and microbial populations that colonized on it (detritusphere) from their comminution and digestion of the leaf litter substrate [1,11,12]. Endogeic/anecic earthworms, on the other hand, may play a significant role in regulating nutrient dynamics in mineral soil and plant root zones (rhizosphere) by their consumption of soil organic matter and root exudates (and depositions) and their active burrowing activity [14][15][16].…”

Invasive earthworms interact with abiotic conditions to influence the invasion of common buckthorn (Rhamnus cathartica)

“…Buckthorn creates ideal conditions for invading European earthworms by providing nutrient-rich leaf litter and creating high-shade conditions that cool soils (Heneghan et al 2007;Holdsworth et al 2008;Heimpel et al 2010). The presence of earthworms in previously earthworm-free forests has many effects on soil properties and nutrient cycling (Bohlen et al 2004;Groffman et al 2004;Frelich et al 2006), reducing the overall availability of nutrients like N and P Costello and Lamberti 2008;Eisenhauer et al 2011;Sackett et al 2013), inhibiting the growth and survival of many native plants (Gundale 2002;Lawrence et al 2003;Frelich et al 2006;Larson et al 2010;McCormick et al 2013) and leading to simplified vegetation layers and reduced tree recruitment (Lawrence et al 2003;Frelich et al 2006;Hale et al 2006;Drouin et al 2014). Once earthworms are established, forest ecosystems may reach a new steady state with novel soil and plant communities and functions (Eisenhauer et al 2011).…”