Effects of grazing disturbance of spatial distribution pattern and interspecies relationship of two desert shrubs

Lei Zhang,Jinrong Li,Yong Gao,Minyu Li,Xiangxin Cui,Zhao Hu,Chao Zhang

doi:10.1007/s11676-021-01353-5

Abstract

Grazing significantly affects the distribution, growth, and productivity of shrubs. In this study, we evaluated the effects of grazing disturbance on the spatial distribution patterns and interspecific relationships of two desert shrubs, Ammopiptanthus mongolicus and Sarcozygium xanthoxylon. Three types of grazing conditions were considered, including enclosed area (EA), seasonal rotational grazing area (SRGA), and grazing area (GA) (100 m × 100 m), in the West Ordos Nature Reserve of Inner Mongolia, China. The results showed that A. mongolicus and S. xanthoxylon populations were uniformly distributed at a small scale, and the distribution in EA and SRGA became gradually random. In GA, A. mongolicus population showed aggregated distribution but S. xanthoxylon population showed random distribution at a small scale. Moreover, both A. mongolicus and S. xanthoxylon populations at the 5–7 m scale showed random distribution. At the small and intermediate scales, the two species showed positive interspecific relationships of GA. However, no interspecific relationship was noted between the two species in EA and SRGA. A significant positive relationship (P < 0.01) was noted between the two species at 2–9 m and a negative relationship (P < 0.01) at 13–17 m scales in GA. Positive relationship (P < 0.01) was noted between the two species at 6–13 m scales and a significant negative relationship (P < 0.01) at 14–24 m scales in SRGA. The two species of desert shrubs showed positive interspecific relationships at the small scale, and they showed negative relationships as the interspecific competition intensified in the presence of grazing disturbance. When the grazing intensity exceeds a certain threshold, the interspecific relationships become weak. Therefore, moderate grazing would facilitate interspecific competition and species succession, whereas excessive grazing would disrupt natural competition causing desertification ultimately.

Highlights

The spatial distribution and relationships among individual populations in the horizontal space represent the distribution pattern combinedly (Lan and Lei 2003)
Vegetation cover, average crown width, and the average height of the shrubs reflect the intensity of livestock grazing in a given area
For A. mongolicus, average height was significantly greater in seasonal rotational grazing area (SRGA), than enclosed area (EA) and grazing area (GA); whereas for S. xanthoxylon, average height was significantly greater in SRGA and EA, than GA (P < 0.05) (Table 2)

Summary

Introduction

The spatial distribution and relationships among individual populations in the horizontal space represent the distribution pattern combinedly (Lan and Lei 2003). Plant species and communities show specific spatial distribution patterns. There are three types of spatial distribution patterns—random, uniform, and aggregated distribution (Zhang 2004; Gu et al 2020). The spatial distribution patterns are formed through various processes. It includes seed dispersal, intra- and interspecies competition, herbivory, and external environmental interference. The spatial distribution patterns of populations can be explored and analyzed to deduce the potential underlying processes (Wiegand and Moloney 2004; Thammanu et al 2021). It is generally believed that the formation of spatial distribution patterns can be attributed to two aspects. There are external environmental factors, such as temperature and precipitation (Legendre and Legendre 1998)

Methods

Results

Discussion

Conclusion