Effects of Sand Dune Stabilization on the Spatial Pattern of Artemisia ordosica Population in Mu Us Desert, Northwest China

Spatial distribution pattern of colonized native semi-shrubs in two artificial vegetation restoration patterns in Mu Us sandy land, North China

Vegetation construction is a key process for restoring and rehabilitating degraded ecosystems. However, the spatial pattern and process of native plants colonized by different vegetation restoration methods in semi-arid sandy land are poorly understood. In this study, two artificial vegetation restoration patterns (P1: row belt restoration pattern of Salix matsudana with low coverage; P2: a living sand barrier pattern of Caryopteris mongolica with low coverage) were selected to analyze the spatial distribution pattern and interspecific association of the colonizing native shrubs. The effects of the two restoration models on the spatial patterns of the main native semi-shrubs of the colonies (i.e., Artemisia ordosica and Corethrodendron lignosum var. leave) were studied using single variable and bivariate transformation point pattern analysis based on Ripley's L function. Our results showed that two restoration patterns significantly facilitated the establishment of A. ordosica and C. lignosum var. leave, with their coverage reaching 17.04% and 22.62%, respectively. In P1, the spatial distribution pattern of colonial shrubs tended to be a random distribution, and there was no spatial correlation between the species. In P2, the colonial shrub aggregation distribution was more dominant, and with the increase in scale, the aggregation distribution changed to a random distribution, whereas the interspecific association was negatively correlated. The differences in the spatial distribution patterns of colonized native semi-shrubs in these two restoration patterns could be related to the life form of planted plants, configuration methods, biological characteristics of colonized plants, and intra- and interspecific relationships of plants. Our results demonstrated that the nurse effect of artificially planted vegetation in the early stage of sand ecological restoration effectively facilitated the near-natural succession of communities. These findings have important implications for ecological restoration of degraded sandy land in the semi-arid region of northern China.

Monitoring the Spatiotemporal Evolution of the Green Dam in Djelfa Province, Algeria

Green walls and green dams are increasingly being considered as part of many national and international desertification initiatives. This paper studies the spatiotemporal evolution of the green dam in the Moudjbara region (Djelfa Province, Algeria), from 1972 to 2019, by using Landsat imagery, Land Change Modeler, and OpenLand package. The future evolution of pine plantations, for the year 2029, was also forecasted, based on an anthropogenic scenario (i.e., anthropogenic pressure is the main driver of the green dam destruction). Our findings revealed that the green dam project was successful for a few years, but, after that, pine plantations deteriorated significantly, due to forest harvesting, livestock overgrazing, and the proliferation of the pine caterpillar processionary, which destroyed most of the reforestation. Land change modeler predicted a huge degradation of pine plantations for the year 2029, and if the deforestation continues at the same rate, the green dam in the Moudjbara region will disappear during the next few decades. Being aware of this threat, the Algerian authorities are now planning to reforest more than 1.2 million ha under the latest rural renewal policy, by introducing new principles related to sustainable development, fighting desertification, and climate change adaptation. We strongly recommend moving away from the singular tree planting focus, to diversifying desertification control methods.

Decadal monitoring of Traganum moquinii's role on foredune morphology of an human impacted arid dunefield

Foredunes in arid zones have been little studied, being significantly different than tropical and temperate foredunes. In the case of the foredune of the arid Canary Islands' dune systems, Traganum moquinii is the predominant plant species, forms nebkhas and nebkhas fields, and acts as a structuring element in the dune field. In this work, the eco-anthropogenic evolution of the foredune surface, and the morphology and distribution of Traganum moquinii species in the Maspalomas dunefield (Gran Canaria, Canary Islands) are analysed, to understand the role that this plant species plays on the foredune's geomorphology and on the biogeomorphological processes altered by human actions. Eight variables were measured in 10 plots at five different times, from the 1960's to the present, through historical aerial photographs and orthophotos, integrated in a GIS. Significant decadal changes in the number and distribution/morphology of Traganum moquinii plants and also in the morphology of the foredune are observed, although not in a spatially homogeneous manner, as three different foredune behaviors are observed. The number of nebkhas/number of T. moquinii plants, has decreased between 1961 and 2012. The largest changes occurred in the north and south of the study area, and the lowest numbers of nebkhas occur where tourist activities and services are intense. In addition, the distance between Traganum moquinii individuals and variables measured in the foredune front (e.g. the diameter of the individuals) have significant relationships. Also, the greater the distance between plant individuals in the foredune front, the greater is the distance of T. moquinii individual plants in the rest of the plot. The alongshore variations in foredune development are due to natural processes (e.g. natural decline or growth of plants), and human impacts (e.g. carpark and kiosk construction, heavy tourist use). This research could be useful for the management of foredunes in arid regions.

Sand dune stabilization changes the vegetation characteristics and soil seed bank and their correlations with environmental factors

Currently the amount of data available on the effect of sand dune stabilization on species conservation in inter-dune lowland is very limited, especially for the sand dune systems in semi-arid regions. In this study, we determined whether the characteristics of above-ground vegetation, soil seed bank and their relationships with environmental factors changed with sand dune stabilization in the inter-dune lowlands in Horqin Sandy Land, China. Species composition, abundance and coverage of aboveground vegetation as well as soil seed bank composition and density were surveyed and their correlations with environmental factors (pH, organic matter content, total nitrogen and total phosphorus) were determined. The results showed that changes in the relationship between aboveground vegetation, soil seed bank and soil quality followed the changes in aboveground vegetation and soil seed banks. Aboveground vegetation species richness increased with sand dune stabilization, but soil seed bank species richness declined. The inter-dune lowland of active sand dunes could provide specific habitats for some endemic species and pioneer psammophyte species as indicated by data on aboveground vegetation and soil seed bank. Our results suggested that both active and stabilized sand dunes should be maintained since active sand dunes are essential for the survival of endemic or pioneer species and stabilized sand dunes are important for sustaining species richness.

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

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 Artemisiaordosica 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.