Evaluation of restoration success for semi-natural and flower meadows in the Oslo municipality

Abstract

While cities are often overlooked as targets for conservation, ecologists have argued that the urban environment is actually a good candidate for re-creating semi-natural meadows, since these nutrient-poor grasslands prefer dry, well-drained soils and are adapted to human disturbance. Although semi-natural meadows are potentially vulnerable to eutrophication and domination by non-target plant species, they are also capable of becoming very species-rich. A number of these meadows have therefore been created or restored in Oslo, Norway in recent years, and this study evaluates the success of these projects.

We surveyed vascular plants (excluding Poaceae) at 11 sites, including 3 calcareous meadows, 3 hay meadows, and 5 generic flower meadows. Despite a severe drought in the growing season of 2018, the majority of our sites appeared to be relatively resilient. On the other hand, the extreme impact to one rooftop meadow showed the importance of adaptive management even for meadows that are expected to be self-sufficient after establishment. We found that, in line with other studies, undisturbed soil was less likely to recruit non-native plants. Commercial soil was not worse than soil from local donor meadows in this regard, but local soil was potentially better able to recruit target species through the preserved seed bank. Non-native plants were additionally associated with high pH and phosphate. Phosphate in particular was high in some sites, possibly due to soil geology, which indicates that pre-restoration soil testing may be necessary.

We found that re-created meadows were generally much more alkaline than reference meadows, suggesting that the project organizer over-estimated the target pH for these sites. We also found that the reference sites were less biodiverse than new sites, possibly due to the exclusion of mosses and lichens from the data, insufficient sampling, or because new sites will lose species over time. Plant family abundances showed clear divisions based on the project organizer responsible for the site, demonstrating the importance of this top-down effect, but were still differentiated based on meadow type. Importantly, we found that the techniques used in this study were straightforward and useful, with some suggestions for improvement.