Fertilization using manure minimizes the trade-offs between biodiversity and forage production in agri-environment scheme grasslands

livestock with high nutrient demands, toward matching the type of livestock and farming sys- tem to the ecosystem to sustain both production and biodiversity. While this approach is unlikely to be appealing to farmers whose goal is to maximize livestock production, it could provide an extra incentive to farmers to join programs aiming to restore and preserve seminat- ural grasslands [see 67]. These programs, so far, highlight the importance of creating floral resources for pollinators to maintain crop pollination. However, enhancing crop pollination is not a main concern for livestock breeders whose production does not rely directly on pollina- tion. The fact that forage from restored areas is suitable for livestock (albeit only some live- stock) after stopping the use of fertilizers could increase farmers’ interest in restoring areas within their farm. Although our study measured responses in relatively small plots, other work has shown that optimization is theoretically possible at landscape scale [27,51]. Yet the strong trade-offs observed in our study suggest that simultaneous maximization of biodiversity and productivity when aiming to restore grassland cannot be achieved within the same management unit. This suggests that delivery will require multi-farm and landscape-scale perspectives [25,51,68]. Fur- ther research is needed to test how choosing plant species that are good for insect communi- ties, especially pollinators, together with nutrient rich and productive species would help to maximize livestock productivity and biodiversity in restored grasslands.

Conclusions There are strong trade-offs between increasing forage production and conservation of insect biodiversity, these being seen even at the low fertilization levels added under agri-environmen- tal schemes. Maintaining the traditional practice of adding farm yard manure offers the overall best point between the two aims. It has a lower impact on biodiversity than the higher fertilizer treatments, and a higher nutrient content in forage than low mineral fertilization. However, if the aim is to restore plant diversity in grasslands, fertilization should stop being used to keep livestock productivity high. Rather alternative livestock should be considered. Intensive farming practices around the world have impacted negatively on grassland biodi- versity for decades [10]. This has led to a variety of policy responses regulating the impact of agricultural intensification. Despite this though, biodiversity loss continues in agricultural sys- tems. Considering multiple perspectives is essential to implement solutions to environmental problems associated with food production [5]. Moreover, rethinking the typical approach of adapting the vegetation (by fertilizing it) to livestock needs, to one of adapting the livestock type to the existing vegetation, could reduce fertilizer inputs and maintain economically viable production. To move this field of research forward by more than incremental amounts, con- servation ecologists and livestock managers need to work collaboratively to devise manage- ment approaches that can achieve a meaningful compromise in delivering both insect

biodiversity and livestock production. In particular, we need more studies that link biodiver- sity and farmers’ profit margins e.g., [69], as these significantly improve our ability to identify sustainable solutions acceptable to both parties. Statement of authorship EVG conceived the main idea which was developed with JM and SS. SS and EVG conducted the statistical analysis and hay sampling. SS designed the randomization analysis and figure for the randomization analysis. SW did the calculation of hay productivity. MF and EVG per- formed the livestock production estimation and forage suitability. EVG wrote the manuscript with input from SS, MF and JM. All authors assisted with revisions. PLOS ONE Manure minimizes trade-offs between biodiversity and forage production in agri-environment scheme PLOS ONE | https://doi.org/10.1371/journal.pone.0290843 October 4, 2023 14 / 18