黄土高原半干旱区退化草地恢复与利用过程研究

草地退化表现为土壤和植被遭到彻底破坏,草地演替过程受到强烈抑制.实验采用长期(30年)封禁措施,定位监测退化草地从次生半裸地演变为近似原生植被(进展演替)的变化过程.结果表明,随着封禁时间的变化,退化草地恢复演替经历了4个阶段,群落盖度、植株密度、物种丰富度和多样性指数、地上生物量和地下生物量在草地群落恢复过程中逐渐增加,其特征变化出现的峰值均在封禁第20年(地下生物量峰值在第15年),其中地上生物量最高达520.5 g/m2;直到封禁的第20~25年,以本氏针茅为建群种的草原群落衰败退化现象明显,而大针茅种群密度剧增;在封禁的第26年以上以大针茅为优势的群落生长较为稳定,从目前群落演替进程看,大针茅有替代本氏针茅的趋势.另外,在草原沟道两侧以斑块状聚集分布有中旱生灌木,群落的演替进入了一个新的阶段.随着封禁时间的延续,退化草地从自然封禁恢复的0~26年,通过侵入-竞争-扩散-定居的几个演替阶段,目前形成以大针茅为建群种相对稳定的"亚顶级".虽然草地生物量有一定下降,但草地质量提高,物种多样性丰富,促进草地的进展演替.草地植物群落主要由禾本科、豆科和菊科组成;多年生植物、C3和旱生物种可以作为草地演替过程和植被恢复的指示物种.长期封育对草地物种更新和生态系统稳定性有负面影响,因此,合理的封育时间是草地生态恢复中非常重要的一个因素.本研究提出,在黄土区退化草地封育10~15年后可以开始进行合理的利用,例如通过两年一次刈割和轻度放牧(2只羊/hm2).本研究可为干旱区、半干旱区相似的退化草地恢复提供理论依据.

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

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/mz. 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 bungeana. 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.