Invasive earthworm and soil litter response to the experimental removal of white‐tailed deer and an invasive shrub

The long-term effects of invasive earthworms on plant community composition and diversity in a hardwood forest in northern Minnesota

Nonnative European earthworms are invading hardwood forests of the Chippewa National Forest, MN. While effects on plant communities at the leading edge of invasion have been studied, little is known about longer-term effects of invasive earthworms. We applied a model using historic O-horizon soil thickness and a chronosequence approach to classify 41 hardwood sites in the Chippewa National Forest as "long-term wormed" (wormed >2 decades), "short-term wormed" or "unwormed/lightly wormed." Graminoids, especially Carex pensylvanica, had the greatest mean percent cover in sites that had been wormed for over two decades. The families with the greatest negative change in mean percent cover after over two decades of earthworm invasion were Asteraceae, Violaceae, and Sapindaceae (specifically Acer species). Across all diversity metrics measured, long-term wormed sites had the lowest understory plant species diversity, short-term wormed sites had intermediate diversity, and unwormed/lightly wormed sites exhibited the highest diversity. Long-term wormed sites had the lowest mean species richness across all sample scales (1-1024 m2). The greatest within-group compositional dissimilarity occurred at sites that had been wormed for over two decades, suggesting that sites that had been wormed for over two decades have not reached a compositionally similar end-state "wormed" community type. Our study suggests that understory diversity will decrease as hardwood forest stands become wormed over time. While our results support other findings that exotic earthworm invasion is associated with lower understory plant diversity in hardwood forests, our study was the first to use space-for-time substitution to document the effects after multiple decades of earthworm invasion.

Research questions to facilitate the future development of European long-term ecosystem research infrastructures: A horizon scanning exercise

Distributed environmental research infrastructures are important to support assessments of the effects of global change on landscapes, ecosystems and society. These infrastructures need to provide continuity to address long-term change, yet be flexible enough to respond to rapid societal and technological developments that modify research priorities. We used a horizon scanning exercise to identify and prioritize emerging research questions for the future development of ecosystem and socio-ecological research infrastructures in Europe. Twenty research questions covered topics related to (i) ecosystem structures and processes, (ii) the impacts of anthropogenic drivers on ecosystems, (iii) ecosystem services and socio-ecological systems and (iv), methods and research infrastructures. Several key priorities for the development of research infrastructures emerged. Addressing complex environmental issues requires the adoption of a whole-system approach, achieved through integration of biotic, abiotic and socio-economic measurements. Interoperability among different research infrastructures needs to be improved by developing standard measurements, harmonizing methods, and establishing capacities and tools for data integration, processing, storage and analysis. Future research infrastructures should support a range of methodological approaches including observation, experiments and modelling. They should also have flexibility to respond to new requirements, for example by adjusting the spatio-temporal design of measurements. When new methods are introduced, compatibility with important long-term data series must be ensured. Finally, indicators, tools, and transdisciplinary approaches to identify, quantify and value ecosystem services across spatial scales and domains need to be advanced.

Experimental effects of white-tailed deer and an invasive shrub on forest ant communities

Ungulate browse and invasive plants exert pressure on plant communities and alter the physical and chemical properties of soils, but little is known about their effects on litter-dwelling arthropods. In particular, ants (Formicidae) are ubiquitous in temperate forests and are sensitive to changes in habitat structure and resources. As ants play many functional roles, changes to ant communities may lead to changes in ecosystem processes. We conducted a long-term experiment that controlled white-tailed deer (Odocoileus virginianus) access and presence of an invasive understory shrub in deciduous forests located in southwestern Ohio, USA from 2011 to 2017. Several leaf-litter ant community responses and litter biomass were measured in five paired deer access and exclosure plots, each with a split-plot removal of Amur honeysuckle (Lonicera maackii). Ant abundance and species richness increased with time in deer exclosures, but not in deer access plots. Honeysuckle removal reduced abundance and richness of ants. There were additive effects of deer and honeysuckle on ant richness, and interactive effects of deer and honeysuckle on ant abundance. Deer exclusion reduced variation in ant composition relative to access plots. There was little evidence that treatments directly influenced species diversity of ants. However, all ant measures were positively related to litter biomass, which was greater in deer exclosures relative to access plots. Our results indicate strong indirect effects of herbivores and honeysuckle on litter-dwelling ants, mediated through changes in litter biomass and likely vegetation structure, which may alter ant-mediated ecosystem processes.