Restoration and Utilization Mechanism of Degraded Grassland in the Semi-arid Region of Loess Plateau

Abstract

Grassland degradation results in a series of ecological problems, such as soil and vegetation destruction, strongly inhibiting succession process of grassland. To research how degraded grassland could be recovered and utilized, we monitored the change progress of degraded grassland from secondary bare land to approximate original vegetation by using long-term grazing exclusion. Results showed the recovery succession process could be divided into four stages with the extending of grazing exclusion time. During the process of community succession, the community coverage, plant density, species richness index, diversity index, aboveground biomass, and belowground biomass increased gradually with the maximum level occurring in the 20th year (except for belowground biomass reaching the peak at the 15th year). The aboveground biomass reached the highest value of 520.5 g/m2. During 20-25 years of gazing exclusion, steppe community with the constructive species of Stipa bungeana degraded obviously, and population density of Stipa grandis grew rapidly. After the 26th year of grazing exclusion, steppe community with the constructive species of Stipa grandis grew stably. According to the community succession process, the tendency was Stipa grandis replaced Stipa bungean a. Xerophytic shrubs were aggregately distributed on both sides of the grass channel and community succession entered a new stage. Through several succession stages from 0-26 years of invasion, competition, diffusion, and ecesis, the grassland had entered the subclimax with the constructive species of Stipa grandis . Even decline in grass biomass, improved grass quality and rich species diversity promote the succession of grassland. Vegetation community consisted mainly of Gramineae, Leguminosae and Compositae. Perennial plant, C3 plant, and xerophytic plant could be used to indicate succession process and vegetation recovery. Long-term grazing exclusion had a negative impact on species generation and ecosystem stability. The reasonable enclosing time played an important role in ecological restoration of grassland. Therefore, we put forward an idea that degraded grassland can be utilized after being fenced for 10-15 years, such as mowing once every two years and light grazing (two sheep/hm2). This study would provide scientific evidence for grassland restoration in arid and semi-arid regions.