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

Zhiyong Zhang, Bo Zhang, Xiao Zhang, Xiaohui Yang, Zhongjie Shi and Yanshu Liu
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Zhiyong Zhang: Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China
Bo Zhang: Beijing Station of the Forestry Science and Technology Extension, Beijing 100029, China
Xiao Zhang: Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China
Xiaohui Yang: Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China
Zhongjie Shi: Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China
Yanshu Liu: Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China

IJERPH, 2019, vol. 16, issue 3, 1-18

Abstract: Ulmus pumila -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 U. pumila seedlings, further inducing population decline. U. pumila 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. U. pumila seedlings had a positive association with their juveniles and Spiraea aquilegifolia, but a negative association with Caragana microphylla . Shrub encroachment occurred with decreasing grazing pressures. In conclusion, overgrazing led to the decline of U. pumila 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 U. pumila population and reduce shrub encroachment.

Keywords: Ulmus pumila -dominated temperate savanna; population structures; spatial patterns; spatial association; grazing pressure; shrub encroachment (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2019
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