For golf courses to support biodiversity and ecological functions such as pollination services, there is a need to convert rough areas into more diverse vegetation. In most cases, this transition is hampered by low seed input and highly competitive grass vegetation under high nutrient conditions. Methods and strategies to overcome these limitations are needed. This project comprised field experiments at Oslo GK and in four other species-poor grasslands in Norway, plus a demo trial at Sigtuna GK, Sweden. These involved a set of treatments to reduce the competitive dominance of grasses (cutting frequency, hay removal, nitrogen immobilisation by sawdust application, seeding of the hemiparasitic species Rhinantus minor) in 2017, and addition of seeds of regional seed mixtures in 2018 to overcome seed limitation In 2020, some of the seeded species had established and some had started to flower, but there were large differences between locations and some differences between treatments. Apart from seeding, removal of cut hay was the single most important management measure to improve plant diversity. Whether the vegetation was cut once or twice was not as important at this stage. Addition of sawdust had no major effect on results. Establishment of Rhinanthus was not successful on most sites, but reduced rough density and improved playing quality at Oslo GK.
Seedling establishment was good in many plots, but the transition from seedling to flowering plants was difficult at four of the five locations. The most likely reason is asymmetric competition, as dense grass was negative for seedling survival. In addition to measures to reduce grass dominance such as cutting and hay removal, a good strategy for sites with dense grass cover is to interseed the more competitive species, e.g. Leuchantemum vulgare, Achillea millefolium and Lotus corniculatus, from the regional species pool.
Three years is a very short time to reduce grass dominance and obtain substantial changes in species composition. Despite that, we found preliminary effects on flower resources and pollinator abundance two years after seeding and three years after initiation of treatments. Contributions to flowering abundance came partly from seeded species, but also from the development of existing species and spontaneous establishment. Treatments to ease establishment of seeded species were also positive for development of species present before seeding.
