Changes in management practices over time explain most variation in vegetation of field margins in Brittany, France

Studies of the effects of modern agriculture on biodiversity have generally lacked a historical perspective. Field margins have considerable ecological significance in agriculture-dominated landscapes, but are affected by interaction with management practices in the margin and on adjoining land. This study investigated the time period over which changes in management practices best explains the occurrence of 40 plant species now commonly found in 311 field margins of Zone Atelier Armorique, Brittany, France. Five management practices were surveyed every year since 1995. Species occurrence was recorded in 2007, 2011 and 2013 and related by means of GLMMs to management practices over time, up to a maximum of 12 years, i.e., scores of field margins on the two first axes of correspondence analysis (CA) performed on management practices. Model selection using AIC criteria allowed us to identify the time period over which to consider management practices that best explain plant patterns. For one third of the common 40 plant species recorded, the time period over which to consider management practices was greater than one year. The rest of the species showed inconsistent patterns with high level of variability between 2007, 2011 and 2013. The time period tended to be longer for species with vegetative reproduction and for zoochorous species. Our results show that the long-term simultaneous monitoring of both vegetation and management practices is important to understand some ecological patterns that would be missed either in short-term studies or for studies that exclude management information. Our findings contribute to long-term strategies for management and conservation of field margins diversity by highlighting that different plant groups require management on particular timescales.