Changes in species diversity, aboveground biomass, and distribution characteristics along an afforestation successional gradient in semiarid Picea crassifolia plantations of Northwestern China

Abstract

Forest plantations play an important role in ecological restoration and economic development in China. To promote conservation of biodiversity and sustainable forest development, analysis of the dynamics of plant species diversity is necessary to guide management strategies. The objectives of this study were to investigate changes in herbaceous community composition, diversity, distribution, and aboveground biomass with age of planted Picea crassifolia stands on two slopes and to determine environmental factors responsible for such changes. Fifty-three species from 22 families and 38 genera were collected along a grassland-afforestation successional gradient during a comprehensive vegetation survey in 2014. The herbaceous community was dominated by species in the Gramineae, followed by the Leguminosae, Compositae, and Rosaceae. Our results showed that afforestation significantly affected community and habitat characteristics. Further, afforestation decreased aboveground biomass and percent cover and increased plant diversity of the herbaceous community. Increasing duration of afforestation was generally associated with lower soil bulk density and pH and with greater soil organic carbon and total nitrogen. Significant differences (P < 0.05) were observed 33 and 45 years after afforestation. Understory composition differed considerably among the different-aged forest stands, and 89.3% of the variance was explained by the measured environmental variables. The differences in soil properties and in the diversity and aboveground biomass of the herbaceous community between afforested and nonafforested grasslands indicated that afforestation provided a “nurse-tree” function for local plant diversity and had a substantial potential to increase soil organic carbon and nitrogen storage.