What we still don't know about weed diversity: A scoping review

Increased agricultural weed diversity is associated with reduced dominance of competitive weeds that reduce crop yields. In addition, diverse weed communities can promote biodiversity at other trophic levels and enhance ecosystem services. For both reasons, there is increasing interest in the relationship between agricultural management and weed diversity. Existing information in this area is limited, relative to the large number of influential factors, but knowledge is increasing rapidly. We conducted a scoping review to determine when, where, and how weed diversity has been evaluated in relation to management. From an initial set of 10 236 items retrieved from Web of Science and Scopus, 7198 were screened and 331 were included. The median publication year was 2015. Nearly half of all studies were conducted in Europe (n = 161, 49%). Organic cropping systems were included in 48 studies (15%). Tillage was the most common management factor (n = 111, 34%), followed by crop rotation (n = 73, 22%). There were 135 studies in which management factors were implemented for six or more years (41%). Most studies included measurements of species richness (n = 265, 80%) and/or Shannon-Wiener diversity (n = 145, 44%). Overall, this review identified a small and heterogenous-but quickly growing-body of literature on weed diversity. Priority areas for future research should include weed diversity beyond field crops in temperate environments, weed seedbanks, functional diversity, and best practices for measuring weed diversity.