Objective The study aimed to reveal the effects of grazing on the diversity of herbaceous plants in Larix principis-rupprechtii plantation and undergrowth under the background of nitrogen deposition.

Method Based on the perennial grazing affected Larix principis-rupprechtii plantation in Mulan paddock in Hebei Province, four treatments of control, closure, fertilization, fertilization + closure were set up. The DBH, tree height, crown width growth and herbaceous biomass and diversity of trees in the sample plot were measured, and the effects of 2-year enclosure and fertilization on the growth and herbaceous diversity of Larix principis-rupprechtii plantation were discussed.

Result Compared with the control plot, closure, fertilization and fertilization + closure treatments promoted the growth of trees. The tree height increased by about 31.7%, 17.6% and 47.5%, respectively. Among them, there was significant difference between fertilization + closure treatment and control. Closure, fertilization and fertilization + closure all promoted the increase of herbaceous biomass. The local aboveground biomass increased by 5.3, 0.4 and 4.1 times, the underground biomass increased by 4.9, 0.1 and 4.3 times, and the total herbaceous biomass increased by 5.1, 0.2 and 4.2 times, respectively. Herb diversity changed little under closure and fertilization treatments, but species dominance changed significantly under different treatments.

Conclusion This study shows that short-term nitrogen addition and closure promote the growth of trees and herbs in Larix principis-rupprechtii forest, have no effects on herbaceous diversity, but significantly change the composition of herbaceous plants.