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Abstract Hysteresis is a fundamental characteristic of alternative stable state theory, yet evidence of hysteresis is rare. In mesic grasslands, fire frequency regulates transition from grass‐ to shrub‐dominated system states. It is uncertain, however, if increasing fire frequency can reverse shrub expansion, or if grass‐shrub dynamics exhibit hysteresis. We implemented annual burning in two infrequently burned grasslands and ceased burning in two grasslands burned annually. With annual fires, grassland composition converged on that of long‐term annually burned vegetation due to rapid recovery of grass cover, although shrubs persisted. When annual burning ceased, shrub cover increased, but community composition did not converge with a long‐term infrequently burned reference site because of stochastic and lagged dispersal by shrubs, reflecting hysteresis. Our results demonstrated that annual burning can slow, but not reverse, shrub encroachment. In addition, reversing fire frequencies resulted in hysteresis because vegetation trajectories from grassland to shrubland differed from those of shrubland to grassland. 

Abstract Plant diversity and plant–consumer/pathogen interactions likely interact to influence ecosystem carbon fluxes but experimental evidence is scarce. We examined how experimental removal of foliar fungi, soil fungi and arthropods from experimental prairies planted with 1, 4 or 16 plant species affected instantaneous rates of carbon uptake (GPP), ecosystem respiration (R_e) and net ecosystem exchange (NEE). Increasing plant diversity increased plant biomass, GPP and R_e, but NEE remained unchanged. Removing foliar fungi increased GPP and NEE, with the greatest effects at low plant diversity. After accounting for plant biomass, we found that removing foliar fungi increased mass‐specific flux rates in the low‐diversity plant communities by altering plant species composition and community‐wide foliar nitrogen content. However, this effect disappeared when soil fungi and arthropods were also removed, demonstrating that both plant diversity and interactions among consumer groups determine the ecosystem‐scale effects of plant–fungal interactions.