Responses of the plant community characteristics and diversity of abandoned grasslands in the Loess Hilly Region in China to slope aspect and year of abandonment

Introduction As key temporal and topographical factors, the year of abandonment and slope aspect significantly affect the restoration process and plant community assembly of abandoned grasslands by altering their microenvironmental conditions. However, how their interactive effects specifically influence the spatiotemporal variations in quantitative characteristics, functional groups, and species or functional diversity of grassland communities remains unclear. Methods In the present study, abandoned grasslands in the Loess Hilly Region, China, were taken as the research objects. The response patterns of the quantitative characteristics of the grassland community, species belonging to different functional groups, and the species or functional diversity of the grassland community to years of abandonment, slope aspect and their interactions were investigated. Results Slope aspect and year of abandonment had significant interactive effects on the quantitative community characteristics, species of each functional group, and species/functional diversity of grasslands. In particular, the dynamic patterns of the above indicators with increasing years of abandonment revealed significant slope aspect heterogeneity. With increasing years of abandonment, all the quantitative characteristics of the shady slope communities tended to continuously decease, or first increase but then decrease, and the species number, biomass, density of each functional group, and community-level species and functional diversity presented similar changes. In contrast, the corresponding indicators of sunny slope communities were dominated by no significant change or an overall increasing trend. Conclusion In general, the overall traits of the abandoned grassland communities on shady slopes tended to improve rapidly, followed by a decline during the succession process, whereas those on sunny slopes tended to be stable or showed overall positive development. To manage the ecological restoration process of abandoned grasslands, different strategies need to be formulated on the basis of slope aspect heterogeneity.