Pollination services, pest control services and crop yield
As different studies used different methods and measures to quantify pollination services, pest control services and crop yield, we standardised data prior to statistical analysis using z -scores (e.g., Garibaldi et al. 2013; Dainese et al. 2019). The use of z -scores has clear advantages compared with other transformations or standardization approaches (such as the division by the absolute value of the maximum observed level of the measured response) because i ) average z -scores follow a normal distribution, and ii ) the variability present in the raw data is not constrained as in other indices that are bound between 0 and 1 (Garibaldi et al. 2013). Pollination services were measured as seed set (number of seeds per fruit), fruit set (proportion of flowers setting fruit), pollen deposition rate (number of pollen grains deposited on stigmas within a certain time period) and, in one study, flower visitation rate (number of visits per flower within a certain time period). If available, differences in pollination service measures of open-pollinated flowers and flowers from which pollinators were excluded were analysed. Measures of pest control services were quantified as pest parasitism (proportion of parasitized pests), pest predation (proportion of predated pests), population growth (see below) or crop damage by pests or pest densities (see Supporting Table S2 for an overview of pollination and pest control service measures across studies). Whenever possible, the pest control index based on population growth proposed by Gardiner et al. (2009) was calculated and analysed (Supporting Table S2). Note that standardized values of pest density and crop damage were multiplied by -1 because lower values of these measures reflect an increased pest control service (e.g., Karpet al . 2018). Crop yield was only considered for the analysis if a direct measure of final crop yield was available. Too few studies assessed crop quality which was therefore not considered further. Yield was measured as crop mass or number of fruits produced per unit area. Due to a lack of studies measuring crop yield in fields with and without adjacent hedgerows, the analysis of crop yield focused on effects of flower strips. Crop yield measures were available from a total of 12 flower strip studies and 194 fields (see Supporting Tables S1 and S2 for a detailed description of study systems, crop yield measures and methods used across studies).