Unpacking the trophic effects of shrubs in arid and semi-arid systems to inform restoration and management.

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Objectives & nature of work*Positive plant interactions are important to diversity and productivity in drylands including grasslands. The consequences of plant facilitation are however generally restricted to single trophic-level effects, i.e. to plant-plant interactions, and not to pollinators, arthropods, or animals. Plant interaction impacts on seedbanks are often overlooked and can be a critical factor in determining community resilience. Direct interactions are also predominantly examined. These research gaps can expand community theory and inform restoration. Accordingly, facilitation in dryland ecosystems such as grasslands or degraded agricultural systems will mediate species loss and provide structural and functional resilience. Nurse-plant studies comprise the majority of research on facilitation in drylands. Nurse plants are shrubs that facilitate the establishment and performance of other plant species, typically annuals. Hence, the management of shrubs in arid systems, degraded grasslands, or agricultural systems with low rainfall in general is vital to maintaining ecosystem function, and this literature is an important avenue of well-articulated research ready for adaptation. In this programme, the overarching hypothesis examined is that nurse-plants are foundation species that provide an anchor for community assembly. The primary purpose is thus to innovate the nurse-plant research by extending to other trophic levels, multiple interaction pathways, and restoration. All research activities are designed to test one of following three broad objectives: (i) to unpack the trophic effects of nurse plants on pollinators, animals, and arthropods, (ii) to resolve many of the direct and indirect interaction pathways of nurse-plants on community dynamics including seedbanks, and (iii) to explore the capacity for shrubs to act as restoration agents in these ecosystems.***Novelty & expected significance*This program directly tests whether strong, basal positive interactions can be used to manage biodiversity in disturbed ecosystems. Each objective is a novel contribution to the fundamental and applied ecological literature. Trophic nurse-plant effects on animals are rarely examined, and there are fewer studies exploring impacts on arthropods or pollinators, i.e. less than 5 studies. Restoration of shrubs is relatively well studied, however using shrubs as the restoration tool is infrequent and a critical paradigm shift. Importantly, the implication of integrating these different concepts experimentally into a research programme is in effect putting the pieces back together for drylands. Trainees associated with the project will thus receive a solid grounding in both theory and application. Integration of interactions will define the foundation species and the community-assembly dynamics in highly impacted systems. This is relevant to policy given global declines of pollinators, the increasing scale and frequency of impacts by humans on these ecosystems, and the likelihood that both invasive species and increased climatic variability will negatively impact species diversity. Effective management of nurse plants will be an important step in maintaining resilience. Canada will benefit from this research because of the following discoveries: linkages between nurse plants and arthropod/pollinator services, mapping novel ecological networks, and identification of best restoration practices. Canadian grasslands and agricultural systems are very similar to the model system proposed. Unfortunately, Canada also shares all of the challenges described above and capitalizing on positive interactions to promote ecosystem function will be critical.