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Increasing local biodiversity in urban environments: Community development in semi-natural species-rich forb vegetation
- Bjørn, Mona Chor, Weiner, Jacob, Kollmann, Johannes, Ørgaard, Marian
- Landscape and urban planning 2019 v.184 pp. 23-31
- Achillea millefolium, Trifolium pratense, aboveground biomass, annuals, biennials, biodiversity, buried seeds, community development, field experimentation, forbs, grasses, growing season, perennials, seedlings, spring, survival rate, urban areas, vegetation types
- There is much interest in supporting biodiversity through eye-catching low maintenance requiring herbaceous vegetation types in urban environments. Community development of forb vegetation is not well understood, and experimental studies investigating the potentials and limitations of establishing such vegetation are needed. We performed a field experiment including three mixtures of 19 forb species (three annuals, three biennials, 13 perennials) and analysed the development of the community over 3 years. In spring 2010 a total of 3630 seedling plug plants were transplanted in a randomized block experiment with 30 plots; non-planted control plots were monitored as reference. Management was limited to removal of dead plant material in February. We documented transplant survivorship, gap colonisation and soil seed bank composition. Standing biomass was harvested in a subset of plots in August 2012, and in all plots in July 2013. After four growing seasons, 1592 transplants were still alive. Fifteen experimental species had spread to gaps, but grasses, Achillea millefolium and Trifolium pratense var. sativum were the most frequent gap-colonizers. On average, biomass of non-experimental species contributed only 11% to the total aboveground biomass in treatment mixtures after four growing seasons. The initial proportions of species (annuals vs perennials) had no significant effect on the community's resistance to colonisation by non-experimental species. Biomass of non-experimental species was negatively correlated to transplant survival. Thus, high plant density increases resistance to invasion, but long-term persistence of forb vegetation is species-specific. In practice some disturbance is necessary to facilitate regeneration of desirable forbs.