Global environmental change effects on plant community composition trajectories depend upon management legacies

The contemporary state of functional traits and species richness in plant communi-ties depends on legacy effects of past disturbances. Whether temporal responses ofcommunity properties to current environmental changes are altered by such legaciesis, however, unknown. We expect global environmental changes to interact withland-use legacies given different community trajectories initiated by prior manage-ment, and subsequent responses to altered resources and conditions. We tested thisexpectation for species richness and functional traits using 1814 survey-resurveyplot pairs of understorey communities from 40 European temperate forest datasets,syntheses of management transitions since the year 1800, and a trait database. Wealso examined how plant community indicators of resources and conditions changedin response to management legacies and environmental change. Community trajec-tories were clearly influenced by interactions between management legacies fromover 200 years ago and environmental change. Importantly, higher rates of nitrogendeposition led to increased species richness and plant height in forests managed lessintensively in 1800 (i.e., high forests), and to decreases in forests with a more inten-sive historical management in 1800 (i.e., coppiced forests). There was evidence thatthese declines in community variables in formerly coppiced forests were amelioratedby increased rates of temperature change between surveys. Responses were gener-ally apparent regardless of sites’contemporary management classifications, althoughsometimes the management transition itself, rather than historic or contemporarymanagement types, better explained understorey responses. Main effects of envi-ronmental change were rare, although higher rates of precipitation change increasedplant height, accompanied by increases in fertility indicator values. Analysis of indi-cator values suggested the importance of directly characterising resources and con-ditions to better understand legacy and environmental change effects. Accountingfor legacies of past disturbance can reconcile contradictory literature results andappears crucial to anticipating future responses to global environmental change.