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. Our
results underscore the dynamical nature of grassland and old field
succession, demonstrating how community properties such as beta-diversity
change through transient and equilibrium states.