THE POSSIBILITIES AND REALITIES ON THE REMANAGEMENT OF DESERTIFIED LANDS IN THE TRANSITIONAL ZONE BETWEEN THE DRY-FARMING AREA AND THE GRAZING AREA IN NORTH CHINA

The desertification process is rapidly developing at present and 61.5% of the land area in the zone are already desertified.Among the desertified lands, 26.9% are seriously desertified, 25% most seriously desertified and 47.4% are the lands where desertification is under way. They are caused by over-reclamation for farming, over-grazing, unreasonable collection of firewood,the destruction of vegetation and the misuse of water resources. Under the ecological environment in semi-arid zone,the degraded environment process possesses the ability of restoring to its original status as soon as the interruption of excessive human activities are eliminated. The fencing- and-self-cultivating method is an effective measure adopted universally in semi-arid zone to cure the desertified lands.The desertified lands can be readjusted and controlled easily if other controlling measures are supplemented. The fundamental ways to control desertification are to utilize rationally the resources, to readjust the existing land     

放牧草地生态系统中氮素的损失和管理

对于大多数放牧草地,Ｎ素都是限制生产力的最重要因素之一,而生态系统中Ｎ素的损失量又很大,Ｎ素以ＮＯ－３、ＮＨ３、Ｎ２Ｏ等形态进入水圈和大气圈,不仅造成了生产上的资源浪费,而且对全球环境和人类健康都产生了深远的影响。本文将对草地生态系统中Ｎ素损失的主要过程（如氮挥发、反硝化和ＮＯ－３淋溶等）及影响因素研究的进展情况进行简要地综述,然后对ＩＭＧＡＲＳＳ项目研究中关于Ｎ素损失研究部分提出一些建议。草地生态系统中Ｎ素损失的主要途径包括：土壤、植物、动物排泄物和肥料的氨挥发;生物和化学反硝化;淋溶;动物体和动物产品对Ｎ素的固持;动植物残体和动物排泄物的燃烧;动物以排泄物形式将Ｎ素从生产区转移到非生产区;通过土壤侵蚀而损失等。放牧加速了草地生态系统中Ｎ素的损失速率。从全球角度分析ＮＨ３的来源后认为,生物残体燃烧是最大的ＮＨ３源,其次是自然土地。对欧洲ＮＨ３来源的研究表明,与人类活动有关的ＮＨ３挥发总量的大部分来源于牲畜排泄物的氨挥发。由于方法的限制,对田间条件下的反硝化测定较少,动物排泄物对Ｎ２Ｏ的贡献及对全球变化影响的研究数据较少。但研究表明,草地尿、粪斑处Ｎ２Ｏ释放速率很高,动物排泄物可能是最重要的Ｎ２Ｏ源。在半干     

青藏高原放牧强度空间化方法与应用

人类活动强度空间化是分析人类活动区域差异及其变化过程的基础,也是准确辨识土地变化驱动因素、合理调控人类活动的科学依据。当前人类活动强度研究多以数理方法对代用指标进行空间化,缺乏对人类活动机理过程的反映,也制约了人类活动强度空间异质性的展现。本文以青藏高原放牧活动为研究对象,在综合放牧喜好和草地管理策略的基础上,从放牧行为机理的角度,提出了区分放牧区与非放牧区的方法;以放牧密度衡量草地整体放牧压力,以放牧概率刻画放牧活动的空间差异,构建了区域放牧强度空间化模型。并以高原典型牧业县—泽库县为例,基于乡镇级牧业数据和自然地理基础信息进行了实证研究。结果表明：空间化结果较好反映了泽库县放牧强度的空间特征;直接指标的选取和客观的赋值方法提高了放牧强度空间化结果的准确性;比现有研究结果更能体现出县域内放牧强度的空间差异,且放牧强度变化过程与同期NDVI值变化具有较好的耦合性。本文为人类活动空间化方法研究提供了有益参考。     

台湾海峡南部夏季微型浮游动物对浮游植物的摄食压力及其生产力

2004年7~8月在台湾海峡南部的5个站位,用稀释法研究了浮游植物的生长率,微型浮游动物对浮游植物的摄食率及其生产力.微型浮游动物主要为无壳纤毛虫,尤其是急游虫类和侠盗虫类.浮游植物的生长率为0.52~0.72/d,浮游动物的摄食率为0.45~1.33/d,相当于每天摄食浮游植物现存量的36%~74%和初级生产力的88%~141%.微型浮游动物的次级生产力(MP02)为初级生产力的28.5%~58.4%.表明微型浮游动物在台湾海峡夏季海洋生态系统的能量流动中发挥着重要的作用.     

Effects of spring–summer grazing on longitudinal dune surface in southern Gurbantunggut Desert

Intensive grazing in spring–summer has been responsible for environmental degradation of the Gurbantunggut Desert in recent years. The coverage of plants and biological crusts, sand surface stability and physicochemical characteristics of soil on the dune surface were conducted in 2002 (winter grazing) and 2005 (spring–summer grazing). The results showed that over 80% of the total area of the dune surface was covered by well-developed biological crusts and plants in 2002, when the interdune and middle to lower part of dune slopes were stabilized and only the crest had 10–40 m wide mobile belt. Affected by spring–summer grazing in 2005, over 80% of the total cover of biological crust was destructed and the plant coverage only reached 1/5 of that in 2002, especially the ephemeral plant cover had a great change. The value of sand transport potential in 2005 only reached 1/3 of that in 2002, but the total surface activity in 2005 was 1.6 times stronger than that in 2002. Meanwhile the mobile area began to expand from the dune top to the whole dune surface following spring–summer grazing. Compared with 2002, medium sand content of the dune surface soil increased by 13.9%, while that of fine and very fine sands decreased by 7.4% and 8.0% respectively in 2005 and the soil organic matter in 2005 was only about 1/2 of that in 2002. It is obvious that the presence of snow cover and frozen soil in winter could avoid the surface structure destruction in winter, while spring–summer grazing made excessive damage to biologic crusts and ephemeral plants. Spring is the main windy season in Gurbantunggut Desert and therefore intensive activity of dune surface occurred following spring–summer grazing, which led to a great loss of fine sand and organic matter. It can be seen that grazing season have a significant influence on the sustainable development of the desert ecosystem in Northwest China.     

Social and ecological constraints on decision making by transhumant pastoralists: a case study from the Moroccan Atlas Mountains

Transhumant pastoralism is an important activity in southern Morocco. Migration pattern of transhumant pastoralists can be affected by physical factors (e.g. droughts and diseases) or socioeconomic factors (e.g. schooling options for children and migration costs). We studied the spatio-temporal rangeland usage of the three tribes Ait Mgoun, Ait Zekri, and Ait Toumert in the south-central Atlas region with a two-fold approach. First, we tracked the migration movements of one representative transhumant herd using the Advanced Research and Global Observation Satellite (ARGOS) collars, which record coordinates from satellite signals. Second, we interviewed herders to obtain information about general grazing practices of the respective tribe and to gain more direct information on motivations underlying decisions. For each tribe we observed small-, medium- and large-scale movements. We found that the most important drivers of migration decisions were seasonal fodder availability and weather conditions in combination with herd-specific risk and cost assessment, as well as personal factors. In conclusion, general migration patterns vary in time, both between and within the tribes, but according to a regulatory framework. Moreover, it appears that both the customary rules and its flexible adaptation to physical constraints are generally beneficial in terms of conservation of the arid and semiarid rangeland resources.     

台湾海峡小型浮游动物的摄食对夏季藻华演替的影响

于2004年8月1~6日对台湾海峡南部近岸的藻华过程进行了定点连续跟踪观测,用稀释法研究了浮游植物的生长率和小型浮游动物对浮游植物的摄食死亡率,同时运用高效液相色谱(HPLC)技术,分析了浮游植物不同光合色素类群的生长率和摄食死亡率.结果表明,观测期间处于藻华的消退期.8月1日时,浮游植物生物量(叶绿素a)和丰度分别为2.04μg/dm3和2.99×105个/dm3,主要优势种为尖刺伪菱形藻(Pseudo-nitzschia pungens)、冰河拟星杆藻(Asterionellopsis glacialis)和中肋骨条藻(Skeletonema costatum),8月6日时,浮游植物生物量和丰度分别减为0.37μg/dm3和1.54×104个/dm3;而蓝藻和甲藻的丰度和比例则呈现出逐渐增加的趋势,所占的比重分别从1日的0.04%和0.85%增加到6日的9.59%和41.97%.小型浮游动物主要由无壳纤毛虫、砂壳纤毛虫、红色中缢虫(Mesodinium rubrum)和异养甲藻等类群组成,总丰度于8月2日达到最大值,为3640个/dm3,之后逐渐减少,6日时,仅为436个/dm3.观测期间,小型浮游动物在群落组成上虽一直以无壳纤毛虫和异养甲藻为主,但在具体的类群结构上却表现出了一定的差异,30μm以下的无壳纤毛虫和异养甲藻总体呈下降的趋势,而红色中缢虫、砂壳纤毛虫和大于50μm的无壳纤毛虫总体呈增加的趋势.观测期间,浮游植物的生长率为0.40~0.91d-1,小型浮游动物的摄食率为0.26~1.34d-1,摄食率和生长率总体呈逐渐下降的趋势.结果还表明,小型浮游动物的摄食率与叶绿素a具有很好的相关性(R2=0.89),对各光合色素类群的现存量和初级生产力均具有较高的摄食压力(分别为37.97%~82.24%和70.71%~281.33%),是藻华消亡的重要原因之一;此外,小型浮游动物对甲藻和蓝藻的避食行为,可能是观测期间由“硅藻”水华向“硅藻-甲藻”水华转变的重要原因之一.     

外来种福寿螺(Pomacea canaliculata)对3种沉水植物的牧食偏好及水体理化因子的响应

外来种福寿螺(Pomacea canaliculata)相较我国本土螺类其牧食量更大且繁殖速度更快,对栖息地水生植物的现存量和实施水生植被恢复的生态治理工程的成功性可能构成威胁,目前对福寿螺影响浅水湖泊沉水植物的重建缺乏足够的研究.本文通过设置不同沉水植物种类组合系统,研究福寿螺对3种常用于浅水富营养化湖泊治理的沉水植物密刺苦草(Vallisneria denseserrulata)、轮叶黑藻(Hydrilla verticillata)、穗花狐尾藻(Myriophyllum spicatum)的牧食偏好以及不同植物配置系统理化因子的响应变化,结果表明福寿螺对沉水植物植株附着偏好为密刺苦草轮叶黑藻穗花狐尾藻,而牧食破坏强度为轮叶黑藻穗花狐尾藻密刺苦草,轮叶黑藻最容易受到福寿螺牧食影响而快速消亡,穗花狐尾藻叶片也会被全部牧食仅剩下茎,而苦草存活受到的影响较小.福寿螺会导致轮叶黑藻+密刺苦草组合系统中总氮、氨氮、总磷、正磷酸盐浓度显著升高,而密刺苦草+穗花狐尾藻组合中总磷、正磷酸盐浓度显著升高,但是在轮叶黑藻+穗花狐尾藻组合中仅总氮浓度显著升高.研究表明福寿螺能够影响沉水植物间的竞争关系,但是3种沉水植物均不能阻止福寿螺的牧食;福寿螺牧食会显著降低沉水植物生物量,最终会影响草型清水态系统的稳定性.     

In-situ studies of microzooplankton grazing pressure on phytoplankton in Jiaozhou Bay, China

Preliminary studies on microzooplankton grazing were conducted with dilution method in Jiaozhou Bay from summer 1998 to spring 1999. Four experiments were carried out at St. 5 located at the center of Jiaozhou Bay. Chlorophyll a concentrations were consistently dominated by netphytoplankton (net-, >20μm), except during the autumn 1998 cruise, when they were dominated by nanophytoplankton(nano-, 2–20μm). The contribution of picophytoplankton (pico-, <2μm) to total chlorophyll a concentrations (<200μm) varied considerably between cruises. Instantaneous growth coefficients(u) of phytoplankton varied from 0.098 to 1.947d⁻¹, with mean value of 0.902d⁻¹. Instantaneous coefficients(g) of microzooplankton grazing on phytoplankton ranged from 0.066 to 0.567d⁻¹, mean value of 0.265d⁻¹, which was equivalent to daily lose of 21.9% of the initial standing stock and 58.1% of the daily potential production. Project No KZCX3-SW-214 supported by Chinese Academy of Sciences.     

Effects of grazing and climate change on sandy grassland ecosystems in Inner Mongolia

To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northern China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land, Inner Mongolia. The results showed that sustained heavy grazing resulted in serious degradation of the vegetation; moderate grazing can maintain vegetation stabilization; and light grazing can promote rapid restoration of degraded vegetation. The livestock productivity was the highest in the moderate grazing grassland, and sustained heavy grazing resulted in rapid decrease of the livestock productivity. Heavy grazing can cause a retrogressive succession of grassland vegetation, whereas moderate and light grazing may promote progressive succession of plant species. The effects of changing climate on succession processes were not significant in the short term; a warm-humid climate is favorable to restoration of degraded vegetation, whereas a sustained warm-drought climate may result in degradation of grassland vegetation. Heavy livestock grazing should be stopped for the sustainable use of grassland; the proper grazing intensity for sandy grassland is two to three sheep or sheep equivalents per hectare in Inner Mongolia.