Disturbance alters transience but nutrients determine equilibria during grassland succession with multiple global change drivers

Disturbance and environmental change may cause communities to converge on a steady state, diverge towards multiple alternative states, or remain in long-term transience. Yet, empirical investigations of successional trajectories are rare, especially in systems experiencing multiple concurrent anthropogenic drivers of change. We examined succession in old field grassland communities subjected to disturbance and nitrogen fertilization using data from a long-term (22-year) experiment. Regardless of initial disturbance, after a decade communities converged on steady states largely determined by resource availability, where species turnover declined as communities approached dynamic equilibria. Species favored by the disturbance were those that eventually came to dominate the highly fertilized plots. Furthermore, disturbance made successional pathways more direct under low nutrients, revealing an important interaction effect between nutrients and disturbance as drivers of community change. O..., Data were collected in successional grassland fields at the Cedar Creek Ecosystem Science Reserve in Minnesota, USA (CDR, Lat: 45.4 Long: 93.2 W) from 1982 to 2004. In 1982, identical disturbance X nutrient addition experiments were established in three abandoned agricultural fields within 5 km of one another that were last tilled and farmed in 1968 (Field A), 1957 (Field B), and 1934 (Field C).
Within each of the three Fields, two grids (35 X 55 m) were established in 1982 for nutrient application, one in an area that was thoroughly disked in the spring of 1982 (E002), and another in an adjacent area that remained intact with old field vegetation (E001). The disking treatment pulverized the existing vegetation, leaving bare soil which was then raked to remove clumps of vegetation. Each grid consisted of 54, 4 X 4 m vegetation plots, receiving one of nine nutrient treatments (applied annually in May or June) in a randomized block design, with 6 replicate plots per field. A nearby remnan...,