Predictive mapping to identify refuges for plant communities threatened by earthworm invasion

Abstract

1. Biological invasions by cryptic ecosystem engineers can alter the ecological and socio-economic values of ecosystems in ways that may take decades to detect.The invasion of North American glacial refuges by non-native earthworms offers a prominent but understudied example of a cryptic invasion. Non-native earthworms are known to alter carbon sequestration, disrupt mycorrhizal networks and homogenize plant communities, but natural resource managers still lack robust protocols to identify and safeguard high conservation value communities (HCVCs) from such invasions. In the absence of such protocols, or reliable methods to eradicate nonnative earthworm populations once established, there is an urgent need for methods to identify HCVCs at risk of or potentially shielded from earthworm invasion by the existence of abiotic barriers to their dispersal or persistence in such sites.2. We developed species distribution models (SDMs) using in situ field surveys and remotely sensed data to (1) identify factors limiting the occurrence of non-native Lumbricus earthworms in imperilled coastal Douglas-fir (Pseudotsuga menziesii) forest and Garry oak (Quercus garryana) and maritime meadow ecosystems endemic to glacial refugia of the Pacific Northwest of North America and to (2) evaluate their influence on plant species diversity and identify abiotic factors capable of preventing their dispersal or persistence at a site.3. As predicted, shallow, drier soils and steeper terrain limited earthworm occurrence and abundance in our highly heterogeneous study area, and earthworm presence appeared to reduce plant species richness. Our results indicated that HCVCs endemic to shallow-soil (< 12 ± 3 cm) sites that experience regular summer drought appear to act as refuges from invasion by non-native earthworms. Our results also elevate concerns for the conservation of deep-soil habitats not isolated from earthworm invasions by shallow soil, saltwater or other barriers to earthworm dispersal. 4. The SDMs developed here offer guidance to the identification of potential refuges for the conservation of imperilled native species and communities from the detrimental effects non-native earthworms in glacial refugia of western North America and should thereby facilitate proactive planning by conservation practitioners.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Invasive earthworms can change understory plant community traits and reduce plant functional diversity

“… 85 , 95 For a more comprehensive approach, and also to avoid any potential confounding effects between the physical distance between areas and the earthworm invasion status, we suggest further studies to cover larger areas in several forests by setting up several clusters of plots, widely separated, inside each of these areas, as for example performed in Fleri and Arcese. 96 Moreover, controlled field experiments on invasive earthworm effects might be a promising approach to investigate causal relationships. 97 We thus stress the need for standardized comparisons of invasive earthworm effects on plant (functional) diversity between multiple forests over time, 98 to be able to gain further insights into the mechanisms that underpin the temporal dynamics of invasive earthworm effects on plant communities and ecosystem functions.…”

Impacts of Invasive Earthworms on Early Life Stages of the Threatened American Hart's-Tongue Fern

“…In our study, upslope locations were consistently closer to potential sources of invasion, such as trails, roads, and homes, corroborating previous observations that earthworm invasions are frequently facilitated by human activity and development (Suárez, Tierney, et al ., 2006; Paudel et al ., 2016; Bellitürk et al ., 2015). Asplenium scolopendrium is also associated with rocky and steep terrain, and thus might be less vulnerable to earthworm invasions and subsequent impacts, as earthworms are less abundant and more likely to be absent from areas with shallower soil and steeper slopes (Fleri and Arcese, 2021; Suárez, Tierney, et al ., 2006). However, earthworms can be carried downslope to A. scolopendrium populations and ravine bottoms by water, especially during storm events, suggesting ferns might experience episodic earthworm dispersal events.…”

“…These annual species are surface dwellers (epi-endogeic), reproduce parthenogenetically with overwintering cocoons, exhibit rapid growth rates and flexible diets, allowing rapid population increases (Moore, Görres, and Reynolds, 2018; Zhang et al ., 2010). Establishment and dispersal of invasive worms is influenced by abiotic factors such as moisture and slope (Fleri and Arcese, 2021), but also by human activities (fishing bait and gardening) and local proximity to human development, especially to roads and garden refuse (Suárez, Tierney, et al ., 2006; Bellitürk et al ., 2015).…”