Summary
Due to a reported increase in vegetation cover in Lake Hafslovatnet bird conservation area, NIVA was asked to map the vegetation in 2015, especially considering the prevalence of common bulbous rush (Juncus bulbosus). This mapping showed no observations of bulbous rush in Lake Hafslovatnet outside the bird protection area. Furthermore, the massive plant growth that was observed in the southern parts of Lake Hafslovatnet in 1990 was not observed in 2015. There was generally much more vegetation within the bird protection area, with high abundances of several of the taller species. In some areas, bulbous rush had accumulated a substantial biomass, but it was not more abundant than a number of other macrophyte species. Lake Hafslovatnet bird conservation area was generally rich in vegetation, and based on this year's survey, we cannot conclude that bulbous rush has increased in abundance or is a dominant species here. Our recommendation is therefore to postpone any planned mechanical or other removal measures, and then resurvey the vegetation once more in 2-3 years, to see if bulbous rush has increased in abundance and/or coverage. After this, one can assess whether removal measures are really necessary and/or desirable, and if so, what kind of measures should be initiated.