Seven years of spider community succession in a Sphagnum farm

Sphagnum farming is paludiculture aiming to produce Sphagnum biomass as a sustainable alternative to peat in horticultural growing media. Here we focus on the habitat value of artificial Sphagnum farming sites for peatland species. We report results from seven years of biodiversity monitoring (2011-2018) in a 14 ha Sphagnum farm in north western Germany, using spiders and harvestmen as indicator groups for succession of invertebrate communities. Species richness and abundance more than doubled in the first two years of Sphagnum growth, but remained rather constant since then. Peatland generalists rapidly colonized the site and constitute some 30%-40% of activity dominance since the second year. Stenotopic peatland spiders arrived later, but their abundance proportion increased significantly from 2014 to 2017. Nevertheless, the spider communities remain distinct from (semi-)natural reference sites. Highly characteristic species of pristine bogs are still lacking. We conclude that a novel community has assembled that bears only moderate resemblance to natural peatlands. Persisting high annual turnover rates in terms of species composition and dominance structure (both. 30%) corroborate high levels of ongoing dynamics and the significance of stochastic processes. The long-term trajectory of community succession in the Sphagnum farm remains vague.