Background: Semi-natural pastures are unfertilized grasslands with a long history of traditional low-input grazing management. This kind of pastures are recognized for their high species richness. However, as a consequence of modernization of agriculture, many of the semi-natural pastures have been lost during the last century, leading to a serious threat to farmland biodiversity. Semi-natural pastures are relatively low in productivity. Hence, to increase profitability, farmers may want to give the grazing animals access to additional nutrient sources. This can be done either as supplementary feeding, or by fencing the semi-natural pastures into the same enclosure as improved, more nutrient-rich, pastures. These practices are, however, controversial. It is argued that since semi-natural pastures are species-rich partly because they are nutrient-poor, introducing additional nutrients into the system should be avoided. Accordingly, in Sweden, these interventions are often prohibited while receiving financial subsidies for management of semi-natural pastures. However, since many farmers are dependent on such support to maintain their pastures, these prohibitions often cause problems. The question has been raised whether giving the grazers access to additional nutrient sources really affect the biodiversity in semi-natural pastures, as is assumed. The primary aim of the proposed systematic review is to answer this question.

Method: Peer-reviewed and grey literature will be searched for using bibliographic databases, search engines, specialist websites and stakeholder contacts. The references will be screened for relevance according to a predefined set of eligibility criteria. The criteria will be tested and clarified iteratively, until consistency in interpretations is achieved. Thereafter, the literature will be screened in two stages, first based upon title and abstract and then by examining full texts. Full text screening will be performed with blinded decisions by two independent reviewers. Each relevant study will then be critically appraised, based on a set of predefined validity criteria. A narrative synthesis will be provided, outlining the evidence base in terms of bibliographic information and study metadata. If possible, quantitative syntheses based on meta-analyses will be performed. Identified relevant knowledge gaps will be highlighted and discussed.