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Trade-offs in multifunctionality of road verges and their delivery of ecosystem services Hans Martin Hanslin Dept. Urban greening and environmental engineering Norwegian institute of bioeconomy research Litterature review for Norwegian road authorities Qualitative review, northern conditions How to integrate multiple functions in verges, focus on pollinators, plant diversity and soil processes Narrow down to a focus on some processes Functions and services Roadverges contributes to ecological functions and ESS in the landscape, a.o. • Habitat function • Dispersal corridor/stepping stone • Resources for pollinators etc • Replacement habitat for grassland species • Source populations for reestablishment • Aesthetic aspects • Noise reduction, trapping pollution, • Intercept runoff and manage stormwater Biodiversity key to high yield of many ESS • regulator of processes • a final ES • a valuable good Key questions How to establish and maintain biodiversity in the long term? Which factors and processes contributes to biodiversity in road verges? Set up against management of invasive species Can you integrate invasion resistance based on biodiversity? S-N grasslands Long history of management – depletion of soil nutrients Species are allowed to complete life cycle Moderate disturbances - cutting and gap creation Cutting lowers competition for light – reduces competitive exclusion Cutting/brosing and other smallscale disturbances create gaps and safe-sites for seedling establishment How relevant are these processes for roadverges? Similar? Differs in many aspects, like: • (higher) nutrient levels • Timing of cutting • Higher and more variable cutting height • Soil physical and chemical conditions • No/delayed removal of cut material • Damages to vegetation cover from machinery • Usually much smaller size and larger border effects • Garbage accumulation, • Higher input of weeds and invasive species etc. • Landscape species pool is lower? Factors Abiotic conditions Landscape Soil Nutrients Water Species pool Connectivity Hydrology Biotic conditions Competition Herbivory Symbionts Management Time/history Site preparation Vegetation establishment Cutting regime Nutrient management Management invasives Seedrain, germination and seedling survival are key processes for invasion Competitive ability important for persistence and dominance Both phases to be targeted by management Prevent establishment by rapidly establish and keep a closed vegetation cover of competitive species tolerant of frequent cutting (mainly grasses) Shortcuts processes promoting biodiversity - cuts of possibilities to regenerate from seeds and increases species turnover Trade-offs High biodiversity Invasive management Cutting frequency Low/Moderate High Clonal growth Low-moderate Strong Less competitive Strong competitors Moderate Low/absent Prevent competitive exclusion Yes No Spontaneous establishment Yes No Mosaic management Yes No Low-high Low Vegetation composition Gap frequency Soil nutrients What to do? Split strategy, depending on invasion risk High risk – Safe solution, grass based, strong competitors, frequent cutting etc Low risk – different options based on landscape context Intermediate risk – Increase the biotic resistance of the system based on priority effects, assembly filters, niche overlaps and redundancy Priority effects Early establishing species get a disproportionate large benefit Strong priority effects are common in many invasive species Niche management Theory – invasability reduced if species with similar traits as invader are present or if available niches are filled. Difficult: similar traits and function, including phenology (vs. seedling stage) Large overlap in function among species – leaving no available opportunities or resources even when species are lost or decline in system – ecological redundancy Assembly filters A combination of abiotic, biotic and dispersal filters can be used to reduce establishment of invasive species. Dispersal filters • landscape management to reduce seed rain Abiotic filter • lower availability of nutrients and water • regular cutting, cutting removal Biotic filters • priority effects, • niche management • cumulative resistance • Plant-soil feedbacks Theoharides & Dukes, 2007 Gaps Gaps are still needed to maintain BD of system to allow regeneration and nonclonal species to persist. Does all this work? Some examples that it does, context dependent? Frankly, more targeted research is needed on how this applies to biodiversity of road verges