Spatial Pattern and Population Structure of Artemisia ordosica Shrub in a Desert Grassland under Enclosure, Northwest China

Abstract

Enclosure is an effective practice for restoring and rehabilitating the degraded grassland ecosystem caused by overgrazing. Shrub species, which are dominant in most desert grasslands in arid and semiarid regions, have some beneficial ecological functions for grassland restoration. However, how the population structure and spatial pattern of the Artemisia ordosica shrub changes in a grassland ecosystem under enclosed practice is not well understood. This study, conducted in the Mu Us desert in northwest China, was designed to measure the A. ordosica population according to the chronosequence of enclosure (enclosure periods ranged from 5 years, 10 years, 15 years, and 25 years), contrasting this with an adjacent continuously grazed grassland. The results showed that the enclosed grasslands had a higher number of individuals of different age classes (seedling, adult, aging, and dead group) and greater population coverage, but shrubs had significant lower (p < 0.05) crown diameter and height in comparison with those in continuously grazed grassland. Further, enclosed grasslands had a significantly higher (p < 0.05) Shannon-Wiener index (H) and Evenness index (E), but a significantly lower (p < 0.05) Richness index (R) than continuously grazed grassland. The crown of A. ordosica showed a significant linear positive correlation with height in all plots across succession, indicating that it was feasible to analyze the age structure by crown. The crown-class distribution structure of the A. ordosica population approximated a Gaussian distribution model in all survey plots. Within the population, seedling and adult groups exhibited aggregated spatial distribution at small scales, while aging and dead A. ordosica groups showed random distribution at almost all scales in different plots. The seedling A. ordosica group showed a positive correlation with adults at small scales in all plots except in 10 years of enclosure. However, it showed independent correlation with aging and dead groups at almost all scales. In long-term enclosed plots, the mortality rate of the A. ordosica population increased, therefore assistance management practices, such as fertilization, mowing, interval grazing, and seasonal grazing, must be employed to maintain population stability after long-term enclosure. This study can improve understanding and clarify the effects of enclosures in the desert grasslands of northwest China.

Effects of different fencing regimes on community structure of degraded desert grasslands on Mu Us desert, China

“…Our results indicated that 11-13 years (moderate time) of fencing would allow vegetation and soil nutrients to recover, while 22-24 years of exclosure might cause a redegradation trend of some community and soil properties. This is consistent with studies in other grasslands (Angassa & Oba, 2010;Liu & Zhang, 2018;Shang et al, 2010;Su et al, 2015;Yan & Tang, 2007). The 11-13 years of seasonal fencing grassland had greater plant density, species richness, biodiversity, and soil physical properties than contemporaneous fencing grassland.…”

“…Some research notes that the restoration process of degraded ecosystem is accompanied with community succession (Deng et al, ; Shang et al, ; Wu et al, ). In restoring grasslands, some tall and strong germinating plants with stronger water and nutrient use, especially Kobresia groups in the study area (Liu & Zhang, ), are gradually demonstrating their competitive advantage in the process of community succession after long‐term fencing, which inhibit the growth of annual groups in herbaceous layer (Deng et al, ). After enclosed for a certain time, the litter accumulation combines with the formation and development of soil crust impedes infiltration of precipitation (Aubert et al, ), which deteriorates soil moisture (Oba et al, ; Read, Duncan, Vesk, & Elith, ; Yang, Chu, Chen, Wang, & Bai, ).…”

Stability and micro‐topographic effects of Sophora moorcroftiana population on a restored alluvial fan, Southern Tibetan Plateau

“…The values in the brackets are the percentages of each class in the total. Population structure is the synthetic action of biological characteristics, environmental factors, and intraspecific interactions that can be used to reflect the succession dynamics and development trends of a population (Liu and Zhang, 2018). The topography had no significant impacts on the SOM and some structural traits of the S. moorcroftiana population.…”

“…The Southern Tibetan Plateau, often called the “Third Pole” of the Earth, is one of the most ecologically vulnerable regions in terms of grassland degradation (Liao et al, 2019; Li et al, 2019). In many dune habitats, shrub species are the crucial element for rehabilitating a degraded grassland ecosystem, because they promote greater substrate stability and decrease sand movement (Liu and Zhang, 2018; Wang et al, 2019). Shrub species are distributed widely across almost the whole Southern Tibetan Plateau and withstand the harsh environment of low oxygen, drought, salinity, and cold temperatures (Zhang et al, 2016; Li et al, 2017).…”

Soil Organic Carbon Mineralization After the Addition of Plant Litter in Yinshanbeilu Desert Steppe under Three Utilization Regimes

“…Mowing, fencing, and grazing are the three most common land use in desert steppe [16,17]. The aboveground biomass, species diversity, and soil nutrient content could be restored after fencing and mowing for a certain period [3,18,19].…”