Degradation and small-scale spatial homogenization of topsoils in intensively-grazed steppes of Northern China

Overgrazing has led to severe degradation and desertification of semi-arid grasslands in Northern China over the last decades. Despite the fact that vegetation is often heterogeneously distributed in semi-arid steppes, little attention has been drawn to the effect of grazing on the spatial distribution of soil properties. We determined the spatial pattern of soil organic carbon (SOC), total nitrogen (N_tot), total sulphur (S_tot), bulk density (BD), pH, Ah thickness, and carbon isotope ratios (δ¹³C) at two continuously grazed (CG) and two ungrazed (UG79 = fenced and excluded from grazing in 1979) sites in Leymus chinensis and Stipa grandis dominated steppe ecosystems in Inner Mongolia, Northern China. Topsoils (0–4 cm) were sampled at each site using a large grid (120 m × 150 m) with 100 sampling points and a small plot (2 m × 2 m) with 40 points. Geostatistics were applied to elucidate the spatial distribution both at field (120 m × 150 m grid) and plant (2 m × 2 m plot) scale. Concentrations and stocks of SOC, N_tot, S_tot were significantly lower and BD significantly higher at both CG sites. At the field scale, semivariograms of these parameters showed a heterogeneous distribution at UG79 sites and a more homogeneous distribution at CG sites, whereas nugget to sill ratios indicated a high small-scale variability. At the plant scale, semivariances of all investigated parameters were one order of magnitude higher at UG79 sites than at CG sites. The heterogeneous pattern of topsoil properties at UG79 sites can be attributed to a mosaic of vegetation patches separated by bare soil. Ranges of autocorrelation were almost congruent with spatial expansions of grass tussocks and shrubs at both steppe types. At CG sites, consumption of biomass by sheep and hoof action removed vegetation patches and led to a homogenization of chemical and physical soil properties. We propose that the spatial distribution of topsoil properties at the plant scale (<2 m) could be used as an indicator for degradation in semi-arid grasslands. Our results further show that the maintenance of heterogeneous vegetation and associated topsoil structures is essential for the accumulation of SOM in semi-arid grassland ecosystems.     

荒漠区啮齿动物优势种与植物因子的关系

[目的]明确荒漠区在不同干扰下植物因子与啮齿动物优势物种之间的相互影响。[方法]研究西北某干旱地区轮牧与过牧干扰下啮齿动物优势种种群的生物量和植物因子之间的关系,并进行灰色关联度及回归分析。[结果]优势物种三趾跳鼠、子午沙鼠和小毛足鼠均与灌木植物有较高的关联度,植物因子对该地区优势鼠种生物量的作用有明显差异,从而形成相互适应、长期共存的格局。[结论]揭示了植物生物量与啮齿动物生物量的变化关系,为研究该荒漠区啮齿动物优势物种群落分布规律提供了参考。     

海南州草地牲畜超载与调控对策

对青海省海南州草地牲畜的超载状况进行了分析研究，提出了海南州草地牲畜的调控对策是：教育和组织群众，自觉按草畜平衡原则组织生产；挖掘生产内部潜力，调整畜群结构；增加科技与生产投入，提高草畜生产能力；建立草原监测制度，为确定合理载畜量提供科学依据。     

Soil organic matter and land degradation in semi-arid area,Israel

Soil organic matter (SOM) was monitored at five research sites along a climatic transect extending from the Judean Mountains (mean annual rainfall 700 mm; annual mean temperature 17 °C) to the Dead Sea (mean annual rainfall < 100 mm; annual mean temperature 23 °C) in Israel. At four sites, representing four climatic regions, Mediterranean (site GIV), semi-arid (site MAL), mildly arid (site MIS) and arid (site KAL), four to eight soil samples were taken four times a year, in January, March, May and September, from 1992 through 1993 and 1994 and in April and August 2000. In the last 2 months soil samples were also taken from another site (MAB) in the semi-arid area. Comparison between the sites along the climatic transect shows that, except for site MAB, SOM increased significantly in both 0–2 cm and 2–10 cm, from the arid site, through the mildly arid site and the semi-arid site, to the Mediterranean site. Analysis of SOM temporal patterns of the two semi-arid sites (MAL and MAB) shows significant change from the normal SOM pattern in both the regional scale and the soil profile scale in one site (MAB). The a-normal pattern of SOM and the low soil aggregate stability at MAB indicates land degradation and it is attributed to overgrazing.     

Population decline of Macaca sylvanus in the middle atlas of Morocco

An eight-year-long census and habitat evaluation of the Macaca sylvanus population was conducted in a 484-km² area of the central region of the Middle Atlas Mountains in Morocco between June 1994 and October 2002. The authors walked a 93.5-km circuit - divided into 16 transect segments - 30 times with teams of trained research assistant volunteers, collecting data on a total of 2,805 linear km. Previous studies had reported an average density of 44-70 individuals per km², while data from the present study indicate a progressive population decline, from 25 to 30 individuals per km², down to a current average density of 7-10 I/km². The population decline is attributed to the loss of prime habitat, mainly cedar forest, which has significantly decreased from 1994 to 2002, due to the growing impact of overgrazing by mixed flocks of goats and sheep and consequent forest degradation. At present, human-caused habitat deterioration in the Middle Atlas risks further compromising the future of the world’s only remaining large M. sylvanus population.     

滇西北德钦县高山、亚高山草甸的人为干扰状况及其后果

调查研究了德钦县高寒灌草甸所承受的人为干扰状况及其后果。结果表明,干扰体中牲畜放牧是澜沧江流域亚高山草甸生态系统中干扰强度最大、频率最高、干扰时间最长、影响后果最严重的人为干扰。过去14年来放牧干扰强度明显增强,牲畜种群数量增加了8.51%,尤其是牦牛(犏牛)增加了16.79%,对草甸生态系统的压力愈来愈大,给德钦草地带来了严重的后果。草场利用面积14年来虽然增加了约15%,但草地总可食生物量却下降了1.7%。其中,高山灌草甸可食生物量分别下降了28.4%和21.9%,亚高山地段的林间草地、疏林草地、亚高山灌丛草地分别下降了12.6%、17.2%和6.9%,生态系统生产力退化明显。草场整体呈退化趋势,局部退化已经相当严重。长期过牧已经导致了一些退化指示植物如鸢尾、橐吾、高山大戟在德钦县形成占优势的群落类型,虽增加了德钦草甸群落的多样性,但降低了草地物种的多样性,引起了德钦畜牧业产品的减少,导致近年来德钦县肉、奶等畜牧产品产量明显下降,严重限制了德钦草地畜牧业系统的持续发展。     

Impact of protection and free grazing on sand dune vegetation in the Rajasthan Desert,India

In the Thar (Rajasthan) Desert of India, sand dunes and sandy plains dominate the landscape. Livestock raising and marginal land cultivation are the main occupations. Owing to the high growth rates of human and livestock populations and a decrease in pasture area and its primary productivity, these lands bear acute grazing pressure. Average rainfall is low and vegetation growth is restricted to the short rainy season of two to four months duration. Often there are years of lower than normal rainfall. In these circumstances, fenced areas, established to stabilize formerly active sand dunes, are increasingly opened to grazing to prevent high stock mortality during droughts. This study was conducted in four fenced and one open site, representative of the region's different vegetation types and grazing pressures. The impact of 2 and 5 per cent free grazing pressure on protected sand dune vegetation density and cover was tested in the two fenced sites. The vegetation data for grazed sites are compared with those for the two ungrazed fenced (protected) and one unfenced (open) site subjected to unlimited grazing pressure throughout the year. The vegetation sampling was carried out by the qaudrat and line-transect method before and after grazing from November 1984 to October 1986. It shows a significant reduction in the density and cover of many palatable species and an increase of unpalatable plants. The effect of vegetation degradation is greater in the unfenced area. The low grazing pressure on the fenced sand dunes sites can still cause drastic changes in the vegetation density and cover. Protection resulted in reduced sand erosion and enhanced growth of palatable plants in the fenced sites under similar climatic and edaphic conditions to the unfenced sites. The grazing pressure in the unfenced areas remains high to extreme during the year, due to low land productivity and high feed demand. The regeneration rate is very slow under the constant (3rd to 5th degree) overgrazing. Low intensity grazing pressure on the fenced sites during droughts can cause heavy utilization and mortality of palatable vegetation.