Seeding wildrye grasses ( Elymus spp.) overcomes litter interactions to slow decomposition in buckthorn‐managed forests ( Rhamnus cathartica )

Abstract Introduction Common buckthorn ( Rhamnus cathartica ) is an invasive shrub that is widespread throughout deciduous forests of North America. Buckthorn benefits more from increased nitrogen availability compared to many native competitors. Increased litter decomposition can be a part of a self‐reinforcing mechanism of invasion. After buckthorn removal, native species and their litter may help slow nutrient cycling. Objectives (1) How does buckthorn invasion and litter affect decomposition of native wildrye ( Elymus spp.) grasses used in understory restoration? (2) Does the impact of mixing buckthorn litter with grass litter influence rye decomposition and does that depend on the environment? Methods We performed a litterbag experiment in an oak‐maple woodland in Minnesota, United States. Over 363 days, we decomposed leaf litters of buckthorn and wildrye independently and in mixture in three settings representative of different stages of forest restoration: intact buckthorn stands, areas where buckthorn was removed, and areas where buckthorn was removed and native species were actively restored. Results Buckthorn leaves had significantly less mass remaining than wildrye. Regardless of species, litters decomposed faster in intact buckthorn stands compared to restored areas. Litter interactions progressed with more time and resulted in significantly enhanced N mineralization. Conclusions Our findings suggest that the differences in decomposition rates among species were so large that actively restoring plant communities can slow nitrogen cycling despite synergistic interactions with mixed litters, with potential desired consequences for dampening invasive performance.