Grazing Altered the Pattern of Woody Plants and Shrub Encroachment in a Temperate Savanna Ecosystem

• Main Authors: Zhiyong Zhang, Bo Zhang, Xiao Zhang, Xiaohui Yang, Zhongjie Shi, Yanshu Liu
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: <i>Ulmus pumila</i>-dominated temperate savanna; population structures; spatial patterns; spatial association; grazing pressure; shrub encroachment
• Online Access: https://www.mdpi.com/1660-4601/16/3/330

<i>Ulmus pumila</i>-dominated temperate savanna is an important tree-grass complex ecosystem in the Otindag sand land, northern China. To date, few investigations have been undertaken on the spatial patterns and structure of this ecosystem and its driving factors under different grazing pressures. The objective of our study therefore is to explore whether grazing has affected the population structure/pattern of woody plants and shrub encroachment in a temperate savanna ecosystem. Results indicate that species richness and seedlings decreased with increasing grazing pressure. An increase in grazing pressure did not significantly affect adult-tree density, but it hindered the normal regeneration of <i>U. pumila</i> seedlings, further inducing population decline. <i>U. pumila</i> seedlings had a more significant aggregated distribution than juvenile or adult trees. The adult and juvenile trees had an aggregated distribution at the small scale and a random distribution at the large scale. Shrubs also showed a significant aggregated distribution. No clear effect on the spatial patterns of adult trees was observed; however, there was a noticeable effect for juveniles and seedlings under different grazing pressures. <i>U. pumila</i> seedlings had a positive association with their juveniles and <i>Spiraea aquilegifolia,</i> but a negative association with <i>Caragana microphylla</i>. Shrub encroachment occurred with decreasing grazing pressures. In conclusion, overgrazing led to the decline of <i>U. pumila</i> population, but the decrease in grazing pressure increased shrub encroachment in the temperate savanna ecosystem. Moderate grazing management may be a better way to enhance the stability of <i>U. pumila</i> population and reduce shrub encroachment.