Tong-Hui Zhang

Variations of sand transportation rates in sandy grasslands along a desertification gradient in northern China

Abstract To assess the variation of sand transportation rate in sandy grasslands at different levels of desertification, sand transportation rates and wind speeds were concurrently measured along a desertification gradient during two windstorm events. Some surface properties (vegetation cover, plant height, soil surface hardness and surface soil moisture) were also measured to quantify their influence on sand transportation rates. Rates increased linearly from the least desertified fixed sandy land to the severely desertified mobile sandy land on both measurement dates. The rate decreased with height by an exponential or power function. Most of the trapped sediments occurred within 12 cm above the surface, suggesting that sand transportation and deposition are near-surface processes. Dry particle size analyses showed that most particles were 0.25–0.1 mm in size, followed in decreasing order by particles of 0.5–0.25, 0.1–0.05, >0.5 and

Sheep gain and species diversity: in sandy grassland, Inner Mongolia

Abstract A grazing experiment was conducted from 1992 to 1996 at a sandy grassland in the Horqin sandy land, located in the northeastern part of China. The grassland had been grazed by sheep for many years before the experiment at an intensity of 4.5 sheep ha−1. The experiment consisted of 4 grazing treatments: no grazing (0 sheep ha−1), light grazing (2 sheep ha−1), moderate grazing (4 sheep ha−1) and overgrazing (6 sheep ha−1). Plant species diversity, plant biomass, soil properties, and sheep liveweight under various grazing treatments were examined. Overgrazing resulted in considerable decreases in both species diversity and plant biomass. As a result, sheep liveweight gain decreased significantly in the last 3 years of the experiment in the overgrazing treatment. No grazing and light grazing treatments had higher species diversity as well as higher biomass production than moderate grazing and overgrazing treatments. The results indicate that light sheep grazing is sufficient for the recovery of overgrazed grassland in this region and for the maintenance of plant species diversity. The proper grazing intensity should be 2–3 sheep or sheep equivalents per hectare for the sandy grassland in Inner Mongolia.

Grassland changes under grazing stress in Horqin sandy grassland in Inner Mongolia, China

Abstract A grazing trial was conducted from 1992 to 1996 in the Horqin sandy grassland area, located in north‐eastern China. The trial had four grazing intensity treatments: no grazing (0 sheep ha−1), light grazing (2 sheep ha−1), moderate grazing (4 sheep ha−1) and overgrazing (6 sheep ha−1) plots. The overgrazing reduced plant diversity by 87%, vegetation cover by 82%, canopy height by 94%, standing crop biomass by 98%, and root biomass by 92% compared with ungrazed grassland in the fifth year. The proportion of poor quality herbages increased to 86%. Non‐grazing assisted recovery of deteriorated vegetation. Though moderate and light grazing also reduced biomass, these treatments did not lead to serious damage to the community species structure. The plant diversity, vegetation cover, and standing biomass in the lightly grazed plots increased over grazing time. The trial showed that a grazing intensity of 2–3 sheep equivalents per hectare was sustainable in the Horqin sandy grassland in Inner Mongolia, China.

Changes in soil properties after afforestation in Horqin Sandy Land, North China

Abstract We studied the changes in soil properties after afforestation on desertification-affected sandy soils to estimate how much time would be required for soils to recover enough for use in sustainable food production. We surveyed soils near and within 3-, 9-, and 19year- old plantations of poplar (Poplus simonii) in the central part of Naiman County, eastern Inner Mongolia, China. Changes in the soil properties following afforestation included an accumulation of fine particles (clay + silt) and soil organic carbon (SOC) in the surface horizons. The contents of fine particles and SOC increased slowly in the first 9-year period and then rapidly between 10 and 19 years, being higher at concave than convex sites. Soil parameters such as available moisture level, amounts of available N and available P, and CEC that control soil fertility showed a similar trend to that of the contents of fine particles and SOC. The contents of fine particles and SOC were higher at the windward edge than in the center of the 19-year-old poplar plantation, suggesting that the accumulation of fine particles was caused by the decrease in wind velocity due to the presence of vegetation. The increase in the SOC content may be caused by the increased carbon input to soils from the vegetation and by the deposition of fine particles with a higher C concentration than that of native sandy soils. Soil fertility, represented by the amounts of available N in the upper 20 cm layer of the soil, recovered after 19 years under poplars, and was similar to that of adjacent fertile cropland. However, the amount of available N under plantations younger than 10 years was lower than that in cropland soils, suggesting that a period of between 10 and 20 years is required for soils to recover from desertified conditions and be utilized for intensive crop farming once again.

Changes in Topographical Features and Soil Properties after Exclosure Combined with Sand‐Fixing Measures in Horqin Sandy Land, Northern China

In a field experiment we evaluated the effects of exclosure and sand-fixing measures on land restoration of shifting sand dunes in a semi-arid, sandy grassland located in Northern China. We fenced an area of about 2.1 ha, enclosing 2 shifting sand dunes—one large and the other small. In 1996, on each dune we applied 2 sand-fixing measures developed in China—burying wheat straw in a checkered pattern (Sc) and planting seedlings of a sand-fixing shrub, Artemisia halodendron (Ar). Changes in the topographical features and soil properties were then monitored for 6 years. The effectiveness of the sand-fixing measures was assessed by monitoring the topographical features and soil properties. Sand dune fixation took 1 year, and a biological soil crust with high contents of soil organic carbon and fine particles (clay+silt) was formed within 3 years. These results are consistent with those reported in previous studies, confirming that such crusts reduce wind erodibility. The effectiveness of exclosure alone, without the other measures, was also implied, especially for the small dune, based on the changes in the topographical features and soil properties outside the exclosure, where a “no-grazing” policy had been implemented from 2000. The rate of soil restoration was higher on the small dune than on the large dune. This was due to the differences in the initial soil conditions caused by the topographical features, suggesting that the capacity of a site to reverse desertification by itself depends on the dune size. Sc was slightly more effective than Ar, presumably because Ar inhibited the invasion of other plant species, whereas Sc allowed invasion of various species. Although the soil properties in the very thin surface crust were restored, the restoration of the soil properties in deeper layers was not significant even after 6 years. It would take a longer time (e.g., 10 to 20 years) for the restoration of the soil properties in deeper layers to sustain more intensive land use in this region.

Impact of land use conversion on soil organic carbon stocks in an agro-pastoral ecotone of Inner Mongolia

Soil organic carbon (SOC) stocks in terrestrial ecosystems vary considerably with land use types. Grassland, forest, and cropland coexist in the agro-pastoral ecotone of Inner Mongolia, China. Using SOC data compiled from literature and field investigations, this study compared SOC stocks and their vertical distributions among three types of ecosystems. The results indicate that grassland had the largest SOC stock, which was 1.5- and 1.8-folds more than stocks in forest and cropland, respectively. Relative to the stock in 0–100 cm depth, grassland held more than 40% of its SOC stock in the upper 20 cm soil layer; forest and cropland both held over 30% of their respective SOC stocks in the upper 20 cm soil layer. SOC stocks in grazed grasslands were remarkably promoted after ≥20 years of grazing exclusion. Conservational cultivation substantially increased the SOC stocks in cropland, especially in the 0–40 cm depth. Stand ages, tree species, and forest types did not have obvious impacts on forest SOC stocks in the study area likely due to the younger stand ages. Our study implies that soil carbon loss should be taken into account during the implementation of ecological projects, such as reclamation and afforestation, in the arid and semi-arid regions of China.

Earlier flowering did not alter pollen limitation in an early flowering shrub under short-term experimental warming

In animal pollinated plants, phenological shifts caused by climate change may have important ecological consequences. However, no empirical evidence exists at present on the consequences that flowering phenology shifts have on the strength of pollen limitation under experimental warming. Here, we investigated the effects of experimental warming on flowering phenology, flower density, reproductive success, and pollen limitation intensity in Caragana microphylla and evaluated whether earlier flowering phenology affected plant reproduction and the level of pollen limitation using warmed and unwarmed open top chambers in the Horqin Sandy Land of Inner Mongolia, northern China. The results of this study indicated that artificial warming markedly advanced flower phenology rather than extending the duration of the flowering. Additionally, warming was found to significantly reduce flower density which led to seed production reduction, since there were insignificant effects observed on fruit set and seed number per fruit. Experimental floral manipulations showed that warming did not affect pollen limitation. These results revealed the negative effects of advanced phenology induced by warming on flower density and reproductive output, as well as the neutral effects on reproductive success and pollen limitation intensity of long surviving plants.

Increased pollinator service and reduced pollen limitation in the fixed dune populations of a desert shrub

Evaluations of restoration success usually focus on the structural aspects of ecosystems. Pollination, as an important functional aspect, is often overlooked. Here, the shifts in pollinator assemblage and pollen limitation in the desert shrub Caragana microphylla were examined along a restoration gradient in Horqin Sand Land, northern China. We identified seven species of bees; however, only four bee species were found to be effective pollinators, with Xanthosaurus remota dominating in the fixed dunes, and with no bee species or only a single species, X. remota, being observed in the semi-fixed and mobile dunes. Flower visitation rate was nearly ten times higher in the fixed dunes than in the mobile and semi-fixed dunes. Experimental floral manipulations revealed that the fixed dune populations experienced less pollen limitation, along with the increase in pollinator availability. Between the mobile and semi-fixed dune populations, pollen limitation was severe and at similar levels. The intensity of pollen limitation was negatively related to pollinator abundance and richness. Overall, the dependence on pollinators for reproduction may be an important constraint that limits persistence in this system. Increased pollinator service during the restoration process may ameliorate pollen limitation, benefiting the restoration of vegetation in this semiarid sandy area.

Effects of Caragana microphylla plantations on organic carbon sequestration in total and labile soil organic carbon fractions in the Horqin Sandy Land, northern China

Afforestation is conducive to soil carbon (C) sequestration in semi-arid regions. However, little is known about the effects of afforestation on sequestrations of total and labile soil organic carbon (SOC) fractions in semi-arid sandy lands. In the present study, we examined the effects of Caragana microphylla Lam. plantations with different ages (12- and 25-year-old) on sequestrations of total SOC as well as labile SOC fractions such as light fraction organic carbon (LFOC) and microbial biomass carbon (MBC). The analyzed samples were taken from soil depths of 0–5 and 5–15 cm under two shrub-related scenarios: under shrubs and between shrubs with moving sand dunes as control sites in the Horqin Sandy Land of northern China. The results showed that the concentrations and storages of total SOC at soil depths of 0–5 and 5–15 cm were higher in 12- and 25-year-old C. microphylla plantations than in moving sand dunes (i.e., control sites), with the highest value observed under shrubs in 25-year-old C. microphylla plantations. Furthermore, the concentrations and storages of LFOC and MBC showed similar patterns with those of total SOC at the same soil depth. The 12-year-old C. microphylla plantations had higher percentages of LFOC concentration to SOC concentration and MBC concentration to SOC concentration than the 25-year-old C. microphylla plantations and moving sand dunes at both soil depths. A significant positive correlation existed among SOC, LFOC, and MBC, implying that restoring the total and labile SOC fractions is possible by afforestation with C. microphylla shrubs in the Horqin Sandy Land. At soil depth of 0–15 cm, the accumulation rate of total SOC under shrubs was higher in young C. microphylla plantations (18.53 g C/(m2•a); 0–12 years) than in old C. microphylla plantations (16.24 g C/(m2•a); 12–25 years), and the accumulation rates of LFOC and MBC under shrubs and between shrubs were also higher in young C. microphylla plantations than in old C. microphylla plantations. It can be concluded that the establishment of C. microphylla in the Horqin Sandy Land may be a good mitigation strategy for SOC sequestration in the surface soils.

Variations of Leaf Economic Spectrum of Eight Dominant Plant Species in Two Successional Stages Under Contrasting Nutrient Supply

ABSTRACT Leaf functional traits are indicators of both plant community and ecosystem responses to environmental factors and can thus increase our capacity to understand ecosystem processes and community assembly due to climate change. The variation in leaf functional traits between succession stages in Horqin Sandy Land is caused by soil nutrient content and by intrinsic biological characteristic of species, but the effects are different. Leaf economic spectra were assessed for seven leaf traits of eight species from early and advanced stages of succession. Species from early succession stages are Agriophyllum squarrosum (L.) Moq., Corispermum macrocarpum Bge., Setaria viridis (L.) Beauv. and Pennisetum centrasiaticum Tzvel., and species from advanced successional stages are Chenopodium acuminatum Willd., Chloris virgate Swartz, Digitaria sanguinalis (L.) Scop. and Leymus secalinus (Georgi) Tzvel. All these species were grown in a greenhouse experiment under two contrasting nutrient supplies including high nutrient level (N+, with 20 g of nutrient addition) and low nutrient level (N-, with no added nutrients). As expected, the resource uptake strategies of the species were affected by soil fertilization addition. Leaf nitrogen content (LNC), leaf phosphorus content (LPC), and photosynthetic capacity per unit leaf area (Aarea) significantly increased at high nutrient level but LPC is more dramatically changed than others leaf traits. Leaf life span (LLS) and specific leaf area (SLA) did not show similar tendency with succession stage. At the same nutrient level, LES still shows different pattern between the early and the advanced succession stages. Species from early succession stages have higher LPC and Aarea, compared to species from advanced stages. Species from early succession stage also tend to have higher SLA and higher LNC than at the advanced succession stage. The LLS did not show any clear changes with succession process. These results provide evidence that LES shift along the succession process is mainly caused by intrinsic biological characteristic of species.