Spatial distribution of benthic algae in the Gangqu River, Shangrila, China

This study consisted of sampling benthic algae at 32 sites in the Gangqu River, an important upstream tributary of the Yangtze River. Our aims were to characterize the benthic algae communities and relationships with environmental variables. Among the 162 taxa observed, Achnanthes linearis and Achnanthes lanceolata var. elliptica were the dominant species (17.10% and 14.30% of the total relative abundance, respectively). Major gradients and principal patterns of variation within the environmental variables were detected by principal component analysis (PCA). Then non-metric multidimensional scaling (NMS) divided all the sites into three groups, which were validated by multi-response permutation procedures (MRPP). Canonical correspondence analysis (CCA) indicated that three environmental variables (TN, TDS, and TP) significantly affected the distribution of benthic algae. Weighted averaging regression and cross-calibration produced strong models for predicting TN and TDS concentration, which enabled selection of algae taxa as potentially sensitive indicators of certain TN and TDS levels: for TN, Achnanthes lanceolata, Achnanthes lanceolata var. elliptica, and Cymbella ventricosa var. semicircularis; for TDS, Cocconeis placentula, Cymbella alpina var. minuta, and Fragilaria virescens. The present study represents an early step in establishing baseline conditions. Further monitoring is suggested to gain a better understanding of this region.

Influence of Potamogeton crispus growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status.

Spatiotemporal heterogeneity of plankton communities in Lake Donghu, China, as revealed by PCR-denaturing gradient gel electrophoresis and its relation to biotic and abiotic factors

The 16S and 18S rRNA genes of planktonic organisms derived from five stations with nutrient gradients in Lake Donghu, China, were studied by PCR-denaturing gradient gel electrophoresis (DGGE) fingerprinting, and the relationships between the genetic diversity of the plankton community and biotic/abiotic factors are discussed. The concentrations of total nitrogen (TN), total phosphorus (TP), NH4-N and As were found to be significantly related (P < 0.05) to morphological composition of the plankton community. Both chemical and morphological analyses suggested that temporal heterogeneity was comparatively higher than spatial heterogeneity in Lake Donghu. Although the morphological composition was not identical to the DGGE fingerprints in characterizing habitat similarity, the two strongest eutrophic stations (I and II) were always initially grouped into one cluster. Canonical correspondence analysis suggested that the factors strongly correlated with the first two ordination axes were seasonally different. The concentrations of TN and TP and the densities of rotifers and crustaceans were generally the main factors related to the DGGE patterns of the plankton communities. The study suggested that genetic diversity as depicted by metagenomic techniques (such as PCR-DGGE fingerprinting) is a promising tool for ecological study of plankton communities and that such techniques are likely to play an increasingly important role in assessing the environmental conditions of aquatic habitats.

Species richness in a riparian plant community along the banks of the Xiangxi River, the Three Gorges region

The distribution of vascular plant species richness along an altitudinal gradient and their relationships with environmental variables, including slope, aspect, bank (flooding) height, and river width of the Xiangxi River, Hubei Province, were examined. Total vascular plant species richness changed with elevation: it increased at lower elevations, reached a maximum in the midreaches and decreased thereafter. In particular, tree and herbaceous species richness were related to altitude. Correlation analysis (Kendall's tau) between species richness and environmental variables indicated that the change in species richness in the riparian zone was determined by riparian environmental factors and characteristics of regional vegetation distribution along the altitudinal gradient. The low species richness at lower elevations resulted from seasonal flooding and human activities - agriculture and fuel collection - and the higher. Species richness ill (he midreaches reflected transitional zones ill natural vegetation types that had had little disturbance. These results oil species distribution in the riparian community could he utilized as a reference for restoration efforts to improve water quality of the emerging reservoir resulting from the Three Gorges Hydroelectric Dam project.

Realization of GaAs/AlGaAs quantum-cascade lasers with high average optical power

Quasi-continuous-wave operation of GaAs/AlGaAs quantum-cascade lasers with high average optical power is demonstrated. Double X-ray diffraction has been used to investigate the quality of the epitaxial material. The compositional gradients and the interface quality are controlled effectively. The corrected average power of per facet about 17 mW and temperature tuning coefficient of the gain peak about 0.91 nm/K from 83 K to 140 K is achieved in pulse operation. Best value of threshold current density is less than 3.0 kA/cm(2) at 83 K. (C) 2005 Elsevier Ltd. All rights reserved.

A multi-frame image super-resolution method

Multi-frame image super-resolution (SR) aims to utilize information from a set of low-resolution (LR) images to compose a high-resolution (HR) one. As it is desirable or essential in many real applications, recent years have witnessed the growing interest in the problem of multi-frame SR reconstruction. This set of algorithms commonly utilizes a linear observation model to construct the relationship between the recorded LR images to the unknown reconstructed HR image estimates. Recently, regularization-based schemes have been demonstrated to be effective because SR reconstruction is actually an ill-posed problem. Working within this promising framework, this paper first proposes two new regularization items, termed as locally adaptive bilateral total variation and consistency of gradients, to keep edges and flat regions, which are implicitly described in LR images, sharp and smooth, respectively. Thereafter, the combination of the proposed regularization items is superior to existing regularization items because it considers both edges and flat regions while existing ones consider only edges. Thorough experimental results show the effectiveness of the new algorithm for SR reconstruction. (C) 2009 Elsevier B.V. All rights reserved.

地面坡度对红壤坡面土壤侵蚀过程的影响研究

通过室内模拟降雨试验,研究了地面坡度对红壤坡面产流过程和侵蚀过程的影响,结果表明:坡面总径流量随坡度的增大呈减小趋势,其中25°坡面比5°坡面的径流量减小22.3%;随坡度的增加,坡面产流达到稳定的历时减少。径流含沙量和坡面侵蚀产沙量随坡度的变化在5°~20°呈增大趋势,而当坡度由20°增加到25°时,径流含沙量和侵蚀产沙量随坡度的增加呈减少的趋势,即在红壤坡面,坡度对侵蚀产沙量影响存在着临界坡度,其值变化于20°~25°之间。

红壤坡面降雨入渗及产流产沙特征试验研究

采用室内模拟降雨研究了不同降雨强度和坡度对红壤坡面降雨入渗、产流产沙的影响。结果表明:产流时间随降雨强度和坡度的增大而提前。对于入渗率较低的红壤坡面,径流强度主要受坡面承雨强度的影响,径流强度随雨强增大而增大,随坡度增大而减小。坡面入渗率随降雨强度的增大表现为先增大后减小。降雨强度增大能够增加水分入渗,但这种促进作用仅在一定的降雨强度范围内起作用。坡面入渗率随坡度增大表现为先增大后减小,20°左右存在一个坡面入渗率变化的临界坡度。坡面细沟侵蚀发展状况对稳定坡面入渗率有比较大的影响。径流率和入渗率与降雨历时的关系分别可以用幂函数和对数函数描述。在75,100 mm/h降雨强度下,产沙量随坡度的增大而增大,而50 mm/h降雨强度下,产沙量在20°时达到最大值而后出现下降,在20°附近存在一个侵蚀产沙量变化的临界坡度。

植物路与土质路产流产沙过程的比较试验

通过室内人工降雨+放水冲刷相结合的方法,对5个坡度(3~18°),5种雨强(1~3mm.min-1),5组放水流量(1.4~9.0kg.m-2.s-1)下的黄棉土土质路面和早熟禾植物路面进行了共60余场次试验,对比分析了植物路相对于土质路侵蚀过程差异及产水、减沙效果。结果表明:在放水冲刷条件下,植物路侵蚀率随放水历时降低,其过程可用对数函数描述;土质路面侵蚀率变化复杂。两类道路的放水流量与侵蚀强度均呈现幂函数变化,且植物道路表现出明显的防蚀作用。雨强增加引起径流量、侵蚀强度增加,土质路的增加快于植物路;坡度增大时,侵蚀强度增大,径流深则为植物路稳定,土质路有小幅增加。植物路相对土质路的减沙幅度为26.24%~47.22%,减少能力可用抛物线方程描述,但植物路较土质路面有利于产生径流,径流深增加幅度平均为58.7%~144.1%,由于径流的泥沙含量大大降低,道路的侵蚀产沙反而有一定降低。

WEPP模型坡面版在黄土丘陵沟壑区的适用性评价——以坡度因子为例

利用安塞试验站1985-1992年的气象观测数据和野外坡度径流小区径流和土壤侵蚀量监测资料,评价了WEPP模型在黄土丘陵沟壑区不同坡度条件下的适用性。结果表明,径流量的模拟值在10°、15°、20°、25°和28°五个坡度条件下,变化幅度不如实测值明显,但模拟值随坡度变化的趋势和实测值相一致;WEPP模型对次降雨、年平均和多年平均土壤侵蚀量模拟结果较好,且无论是模拟值在不同坡度之间的差值、还是模拟值随坡度变化趋势均与实测值接近。I30对WEPP模型模拟次降雨径流量有重要影响,当I30大于0.92mm/min,模型模拟误差较大。WEPP模型对次降雨土壤侵蚀量的模拟与PI30密切相关,当PI30大于129mm2/min时,模型模拟误差较大。∑PI30对WEPP模型模拟年平均径流量和侵蚀量有重要影响,当∑PI30大于150mm2/min时,模拟精度明显下降,且∑PI30对径流模拟影响较对土壤侵蚀模拟影响明显。WEPP模型对次降雨、年平均和多年平均径流量模拟的Nash-Sutcliffe有效性ME分别为0.914、0.912和0.617;对次降雨、年平均和多年平均土壤侵蚀量模拟的Nash-Sutcliffe有效性ME...

Investigation on the strain relaxation of InGaN layer and its effects on the InGaN structural and optical properties

The evolution of strain and structural properties of thick epitaxial InGaN layers grown on GaN with different thicknesses are investigated. It is found that, with increase in InGaN thickness, plastic relaxation via misfit dislocation generation becomes a more important strain relaxation mechanism. Accompanied with the relaxation of compressive strain, the In composition of InGaN layer increases and induces an apparent red-shift of the cathodoluminescence peak of the InGaN layer. On the other hand, the plastic relaxation process results in a high defect density, which degrades the structural and optical properties of InGaN layers. A transition layer region with both strain and In composition gradients is found to exist in the 450-nm-thick InGaN layer.

Strain gradient theory based on a new framework of non-local model

A new framework of non-local model for the strain energy density is proposed in this paper. The global strain energy density of the representative volume element is treated as a non-local variable and can be obtained through a special integral of the local strain energy density. The local strain energy density is assumed to be dependent on both the strain and the rotation-gradient. As a result of the non-local model, a new strain gradient theory is derived directly, in which the first and second strain gradients, as well as the triadic and tetradic stress, are introduced in the context of work conjugate. For power law hardening materials, size effects in thin metallic wire torsion and ultra-thin cantilever beam bend are investigated. It is found that the result predicted by the theoretical model is well consistent with the experimental data for the thin wire torsion. On the other hand, the calculation result for the micro-cantilever beam bend clearly shows the size effect.

九寨沟湖泊湿地植物群落与植物地理研究

九寨沟湖泊湿地在维持九寨沟的生态平衡中起着重要的作用，在旅游产业的发展下，湿地生态系统及生物多样性面临着较大的威胁。尽管九寨沟湿地具有重要的生态价值，但目前对其研究尚比较薄弱。湿地植物群落和植物地理研究可以为湿地资源的可持续利用和监测保护提供科学依据。作者从2004年8月到2007年11月对九寨沟湿地的植物物种组成、地理分布、优势植物群落的结构、生长动态、湿地土壤种子库进行了调查研究。主要结果如下： 1. 九寨沟湿地物种组成、地理分布特点及湿地植物群落特点 九寨沟湿地共有苔藓植物8科13属16种，维管植物为48科107属199种。九寨沟湿地植物的地理成份较为丰富，维管植物在科级水平上有7种地理分布型（变型），在属级水平上有13种地理分布型（变型）， 在种级水平上共有29种地理分布型（变型）。九寨沟湿地植物以温带成份和我国特有成份为主，同时兼有热带、亚热带成份和环极—高山成份。九寨沟湿地植物的分布表现出明显的垂直地带性和水平地带性。湿地植物群落可划分21个群落类型，不同植物群落类型的物种多样性及物种组成存在较大的差异。九寨沟湿地植物的物种多样性和群落多样性以及较高的生产力特征，是维持其湿地生态景观多样性和稳定性的基础。 2. 土壤、水环境、海拔等对湿地植物的分布及生物多样性的影响 九寨沟湿地土壤、水等环境因子存在较大的差异。帕米尔苔草和宽叶香蒲等群落的凋落物较多，土壤有机碳、土壤总磷较高，可能是九寨沟湿地的重要土壤碳库。 九寨沟湿地植物沿水环境梯度的分布规律表现为：沉水植物（轮藻—篦齿眼子菜，水苦荬，杉叶藻）——挺水植物（水木贼，芦苇，宽叶香蒲）——湿生草本（苔草、节节草、披散木贼）——湿生灌木（柳灌丛，小檗灌丛）等。海拔也影响湿地植物的物种组成。 水深对物种多样性有影响，水深与物种丰富度负相关。随着水深的增加，水木贼、芦苇、杉叶藻、宽叶香蒲等群落的物种多样性下降；在长期淹水和季节性淹水的地方，水木贼群落物种多样性存在显著差异。土壤总氮与水木贼群落物种丰富度正相关。 3. 土壤营养元素、水环境对植物生长的影响 水深影响湿地植物生物量的分配。芦苇无性系分株在47 cm水深的环境中单株平均生物量最大；在干滩地中（地面水深0 cm），叶生物量百分比最大，而茎生物量百分比最小，茎的生物量百分比和生长速率随水深的增加而增加；在较干的滩地生境中，开花率、花序的生物量百分比明显大于水较深的生境。 水深与水木贼地上生物量负相关，但水木贼地上生物量在长期淹水和季节性淹水的地方没有显著的差异。在水浅的地方，杉叶藻、水木贼、芦苇等植物群落中，其他伴生物种的生物量占样方总生物量的百分比较大。 土壤有机碳、土壤总氮、土壤总磷等对湿地植物生物量的影响比较大：宽叶香蒲地上生物量与土壤总磷正相关；水木贼地上生物量与土壤总氮正相关；杉叶藻地上生物量与土壤有机碳正相关。 水深、土壤营养成分对湿地植物高度、密度等有影响。水木贼的平均高度在季节性淹水的地方比长期淹水的地方低，平均密度在长期淹水的地方比季节性淹水的地方低；除了5月份，其他观察月份水木贼的密度都与水深负相关，同时与土壤有机碳正相关。另外，芦苇密度与土壤有机碳含量正相关，宽叶香蒲密度与水深负相关，帕米尔苔草高度与土壤有机碳负相关。 4. 优势植物群落的动态变化 在优势植物群落中，优势种的高度、密度、盖度、生物量等在群落中占绝对优势。除五花海，水木贼群落的物种组成、高度、生物量在两年间没有显著的变化。芦苇群落的物种丰富度在近两年有所增加。 湿地植物生长表现为明显的季节动态，生长的峰值大多在7月－8月。优势植物群落的物候与水文周期有关。湿地植物群落的物种组成和密度，可以作为对湿地监测和保护的生物指示。 5. 九寨沟湿地土壤种子库特征及其在湿地生物多样性恢复中的作用 水深和现存植被物种丰富度可以解释湿地土壤种子库的变化。水深可以解释表层物种丰富度45%的变化。现存植被物种丰富度可以分别解释10 cm土层、2－5 cm土层及5－10 cm土层土壤种子库45%、48%和25%的变化。 湿地土壤种子库的密度为0－15945粒m-2, 种子库中共发现23个物种。现存植被优势物种和种子库优势物种不同。各层土壤种子库密度和物种丰富度并不存在显著的差异，但第二层土壤种子库密度最大。海拔、现存植被优势种盖度、土壤总磷、土壤总氮、土壤有机碳对湿地土壤种子库的密度和垂直结构没有影响。土壤种子库物种丰富度小于地上植被物种丰富度。湿地土壤种子库与地上植被的相关性不大。在浅水区域，湿地土壤种子库在湿地植被恢复中有一定作用。但在深水区域，保护现存植被更重要。 The lakeshore wetlands are valuable ecological units of the Jiuzhaigou lakes. Pressure for travel industry development pose a continuing and severe threat to the biodiversity-support function of the wetland system. Despite the ecological importance of wetlands in Jiuzhaigou, they are so far poorly studied. Both general plant communties and biogeographical studies are needed in order to attain basis for sustainable use the wetland resources and adequate protection of these areas. The present study was undertaken to examine aquatic plants distribution and the species compositon, structure and growth dynamics of their communities with variations of environmental factors along altitudes, water depth and soil properities gradients in Jiuzhaigou. Analysis of field survey data collected during August 2004 and November 2007 in lakeshore wetlands in Jiuzhaigou National Nature Reserve, Sichuan, China. The results were as following: (i) Species composition and biogeography in wetland vegetation 8 families, 13 genus, 16 species of moss and 48 families, 107 genus and 199 species of vascular plants in Jiuzhaigou wetlands were found. The floristic compositions were abundunt. Ten geographical distribution types at family level, 13 geographical distributions types at generic level and 29 geographical distribution types at specific level in vascular plants were found. Most species in Jiuzhaigou wetlands are temperate elements and Chinese endemic elements, with a few of tropical and subtropical and some circumarctic elements. And the plant distributions show clear vertical and horizontal patterns. There were 21 major wetland plant community types. Species composition and species richness in different plant communities are different. The species diversity and plant community diversity and their high biomass are the basis for the diversity and stability of wetland landscapes in Jiuzhaigou. (ii) Water depth, soil nutrients and altitudes influence on the species diversity and plant distribution. Total phosphorous and organic cabon in soil were higher in C. pamiernensis and T. latifolia communities, where are important cabon reservoirs in Jiuzhaigou wetlands. Along gradients of water depth, among populations of the dominant plant species present: submerged macrophytes (Chara vulgaris, Potagemonton pectinatus, Veronica anagalis-aquatica，Hippuris vulgaris), emergent macrophytes (Equisetum fluviatile, Phragamites australis, Typha latifolia), helophytes (Carex pamirensis )and shrubs (Salix sp., Berberis sp. ). Altitudes influence on the assemblage of plant communities. Water depth negatively correlated with species richness. Specie richness showed differences between permanently flooded sites and seasonally flooded sites in E. fluvatile communities. And total nitrogen in soil was negatively correlated with species richness in E. fluviatile communities. Altitudes show no significant influence on species richness, but in fact, through our analyses, they do have influence on the assemblage of wetland plants. (iii) Water depth, soil nutrients influence on the plant growth Water depth influences the biomass allocation in Phragmities australis. The average aboveground biomass of a single ramet (4.2 g) was the largest in the habitat with water level 47 cm above the soil surface. At the habitat with water level under soil surface 15 cm (－15 cm), the leaf biomass percentage (of the total ramet biomass) was the largest (46.1%), and the height and percentage of ramose ramets ( with branches on stem )(of the total ramets in a plot) were found obviously different. The deeper in water, the larger the biomass percentage and growth rate of stems were. The flowering rate and biomass of panicles were greater in shallow water than those in deep water. Water depth negatively correlated with aboveground biomass of E. fluviatile. However, above-ground biomass of E. fluviatile showed no significant difference between permanently flooded sites and seasonally flooded sites. But in shallow water, more biomasses of accompanying species were found in dominant plant communities such as H. vulgaris communities, E. fluviatile communities and P. australis communities. Water depth, soil nutrients influence on shoot density and shoot length of wetland plants. The shoot density of E. fluviatile was correlated to water depth in all growth months. Annual average density was significantly lower at permanently flooded sites than at seasonally flooded sites. But the annual average shoot length was significantly lower at seasonally flooded sites than at permanently flooded sites. (iv) Growth dynamics of dominant communities in Jiuzhaigou wetland The shoot length and shoot density, coverage and biomass of domiant species were dominated in plant communities. The species composition increased in P. australis communities in recent two years. The species richness in E. fluviatile communities showed no difference between 2005 and 2007. The above-ground biomass and shoot density in Five－flower Lake from July 2005 to July 2007 were significantly different, while in other sites, the differences were not significant. Shoot height, shoot density and above-ground biomass showed significant seasonal changes in all sites. Growth dynamics correlated with the cycle of water levels in lakes. Most plants growth parameters peaked at July or August. The biomass of T. latifolia peaked in August. But the shoot length of T. latifolia in deeper water peaked in July. The shoot length of E. fluviatile increased significantly from May to August except in seasonally flooded sites in Arrow-bamboo Lake. The species composition of communities and shoot density can be used as bioindicators in Jiuzhaigou wetland. (v) Soil seed bank in Jiuzhaigou wetland and its role in vegetation restoration Seed density in all soil layer samples was negatively correlated to water depth. Water depth can explain 45% variance of species richness in surface layer in sediment. Species richness in extant vegetation can explain 45%, 48%, 25% variance of species richness in total 10 cm and in 2－5 cm and 5－10 cm layer sediment respectively. Mean seed densities in wetlands ranged from 0 to 15945 m–2. A total of 23 species germinated in seed bank. The dominant species in seed bank and extant vegetation showed great difference. The total number of species and seedlings that germinated in different layers was not significantly different. But the second layer had the greatest seed density. In shallow water, seed bank can contribute to vegetation restoration, while in deeper water, protection of extant vegetation may be a better strategy.

青藏高原东部混农季节性放牧及其对高山林线格局的影响

混农季节性放牧（agropastoral transhumance）通过作物种植和畜牧生产相结合的方式对不同海拔高度带上的资源进行相互补充利用，在亚洲兴都库什地区、青藏高原、横断山、东部及南部非洲、南美安第斯地区等具有悠久的历史。这种传统的生计系统几千年以来一直是居住在该地区的人类社会和自然生态系统相互作用的主要形式之一。这种传统的资源利用方式与山地自然植被以及特殊的山地人类文化和社会特征具有密切的协同演变关系。认识和理解这一关系，是山地生态学和人类学的核心科学问题之一。近年来，山地生态系统的多重功能性及动态演变对山区社会经济可持续发展的重要意义受到人们的不断关注。本文通过对云南省德钦县的12个自然村的混农季节性放牧以及对云南德钦、四川壤塘等山地植被格局特别是高海拔地带植被格局的的详细调查，探讨青藏高原东缘地区混农季节性放牧的主要特征、系统构成及相互关系，及其在全球变化、经济全球化和市场化及现代化过程中的变化趋势，分析混农季节性放牧与高山林线格局及生态系统的互动关系，旨在探讨山地地区人类活动与自然生态系统之间的互动关系，从而为山区社会经济可持续发展、环境建设和生物多样性保护等国家战略提供理论依据。 调查结果表明，混农季节性放牧是一种适应青藏高原东部高山峡谷地区环境因子及自然资源呈明显的垂直分布、资源数量稀少而时空分布异质性极高的生存环境的一种传统经济形式。这种传统的畜牧业的主要生产目的仍然是提供当地基本生存所需的产品，饲养牲口的种类和数量取决于农户的当地需求并且受资源的限制，因而维持在比较低的水平的。分布在不同海拔高度的放牧资源在一年中被牲口利用的时间也不同，互为补充，共同构成混农季节性放牧的资源基础。根据各社区永久居住点的位置和该村的土地资源特别是牧草地资源的分布范围，牲口迁移的距离和格局有较大的差异。。天然牧场仍然是最主要的畜牧业生产资源。混农季节性放牧中的农业系统和牧业系统互为补充，共同构成调查地区完整的的生计系统，农耕活动为放牧活动提供精饲料如粮食等和冬季饲料如秸秆， 其数量往往成为家庭畜牧业生产规模的主要决定因子之一。 通过对牲口数量和结构、牲口的时空迁移格局、牧业活动在整个经济活动中的相对重要性以及牧业活动和作物种植的关系方面的研究分析，混农季节性放牧在近几十年发生了深刻的变化。主要表现在牲口数量总体下降，牲口组成发生变化，牲口移动性降低、牧业活动的经济重要性下降以及牧业活动和种植活动之间的相互依存度降低等。上述变化的根本驱动力是发生在当地、地区及全球尺度上的环境、政治、社会经济、技术和文化等的变化，从而造成当地群众畜牧生产目标、土地利用和劳动力的分布等发生了变化。当地生计系统发生的改变可能会带来对方面而深刻的政治、社会经济、文化和生态影响。 混农季节性放牧这种古老的传统生计策略面临着许多挑战，如冬季饲料短缺、草场退化、缺乏市场竞争力、经济重要性降低、对年轻人缺乏吸引力、国家缺乏专门的政策指导等。与此同时，经济全球化、市场经济、新技术的应用、替代生计机会的增加、国家对于山地生态系统的作用的重新定位等也为传统生计系统转型、实现社会与生态共赢创造了机遇。 混农季节性放牧活动对亚高山及树线交错带生态系统系统的互动方式主要体现在以下几个方面：（1）牲口啃食、践踏等影响森林群落更新，改变森林群落的组成和结构，从而影响森林群落的演替进程和植被格局。林线边缘是搭建夏棚的首选地点，因此林线及树线交错地带就成了牲口活动的主要场所之一；（2）利用火烧开辟、维持和改良高山牧场； 3）在亚高山火灾迹地的放牧活动能够阻止火烧迹地的顺向演替； 4）牧民在林线附近获取建材和薪材等活动影响高山林线附近森林的结构和功能。 在调查区域，梅里雪山、白马雪山、甲午雪山的林线海拔高度在4200-4300m之间； 四川雅江、理塘一线，林线位置多在4300-4400m；四川壤塘二林场一带的林线主体在4100-4200m，在个别地区达到4300m； 在贡嘎山的南坡和东坡一带，林线位置在3600-3700m；而在四川松潘一带，林线位置主体在3700-3800米左右。树线高度的分布趋势和林线一致。混农季节性放牧及其有关人类利用活动使研究地区很多地方高山林线降低、树线交错带宽变窄或消失。在研究地区，总体情况是，阳坡和半阳坡（南坡、西南坡等）的林线和树线比阴坡和半阴坡（北坡、东北坡等）低，变化幅度达20-200m。这种差异主要是为了开辟牧场而人为清除了南向坡自然林线及其以上的植被从而使林线位置下降所致。在南坡自然林线保留得比较好的地方，林线和树线依然可以达到甚至超过北坡林线和树线的高度。放牧活动抑制了高山林线带火烧迹地的天然更新，从而使林线位置保持在目前的位置。 放牧活动对高山林线带森林群落更新的影响是显著的。自然林线内的乔木个体密度特别是新生苗和幼苗的密度大大高于非自然林线。没有放牧的自然林线及树线交错带内的I级个体（新生苗）密度达到725-2917株/公顷，而与之相对的处理样地内I级个体的密度只有0-228株/公顷；II级个体（高度10-50cm）也表现出类似的趋势，在没有放牧的自然林线及树线交错带样方内，其密度达到550-5208株/，而在放牧处理样方内只有14-321株/公顷。在非自然林线带样地内，在有正常放牧的样地内，完全缺乏I级个体。 从相对比例来看，没有放牧的样方内的I、II级个体在全部个体中所占的比例显著高于有放牧活动的样方。放牧使林线交错带的乔木幼苗数量显著减少，从而影响林线及树线交错带森林群落的天然更新过程。林线和树线交错带的灌木对乔木幼苗具有重要的保护作用，能够为树线树种如冷杉等幼苗的定居体提供有利的微气候环境，同时保护苗免受牲口的啃食和践踏。火烧以后接着进行放牧能够100%地抑制高山林线带的幼苗更新。 高山牧场放牧强度降低、使用时间缩短而低海拔地带放牧强度增加是研究地区混农季节性放牧系统的一个显著变化。这种变化也必然会引起各海拔带上的生态系统的变化。放牧强度的降低、生产性用火的停止将导致原来通过人工火烧而降低并通过进一步的火烧和放牧活动来维持的林线及其以上地带的灌木盖度和高度的增加，从而为林线森林群落的扩张创造条件。 青藏高原东部高山峡谷地区是我国重要的山地生态系统，在我国的生物多样性保护、生态环境建设、社会经济可持续发展战略中具有举足轻重的作用。正确认识人类特别是当地传统的生计系统与生态环境系统的互动关系是实现上述战略目标的前提。决策者必须以综合、系统的的视角协调促进社会经济可持续发展、保护生物及文化多样性和维持人、牲口和生态系统之间的平衡的多重目标。 Agropastoral transhumance, which makes a complementary exploitation of the natural resources at different altitudinal belts through a combination of migratory animal husbandry and crop cultivation, has a long history in Hindu-Kush Himalaya, Tibet Plateau, Hengduan Ranges, eastern and southern Africa and the Andes region of south America.For millennia, this traditional livelihood strategy has been one of the main forms of interaction between human societies inhabiting in these regions and their natural ecocystems. A close co-evolutionary relationship has been developed between this indigenous resources management systems and the mountain vegetation systems on the one hand and a unique set of cultural values and social features on the other. Understanding this relationship has been one of the core scientific issues in mountain ecology and anthropology. In recent years, the importance of the multiple functions of the mountain ecosystems and their dynamic changes in the sustainable socio-economic development of the mountain regions has gained increasing attention. This paper, which is based on a detailed study on the agropastoral practices of the 12 natural villages in Deqin County of Yunnan, and the mountainnn vegetation patterns in Deqin of Yunnan and Rangtang County of Sichuan, intends to reveal the major characteristics, system composition and the inter-relations of the subsystems of the agropastoral transhumance in Eastern Tibetan Plateau as well as the trends of changes of the system within the context of global changes, economic globalization and modernity process of China and analyze the relations between agropastoral transhumance and alpine ecosystem, ao as to understand the interactions between human activities and natural ecosystems of the mountains and provide theoretical basis for the national strategies in eocioeconomic development, environmental reconstruction and biodiversity conservation in the mountain regions. Results of the survey indicate that agropastoral transhumance in the investigated area is a traditional economic form that is highly adapted to the eastern Tibet Plateau where the topography features high peaks and deep gorges and where the highly variable environmental parameters and scanty natural resources exhibit a distinct vertical spectrum of distribution and great temporal and spatial heterogeneity. The main objective of pastoral management is still aimed at the production of basic goods and services of local people and thus the type and size of animals raised for each household mainly depend on local needs and are limited by the availability of natural resources. The scale of production is relatively low. Pastoral resources at different altidudinal belts are complementarily used at different seasons of a year and thus form the resources basis for agropastoral production of the study area. Migration distances and patterns vary with the location of the permanent settlements, the elevational distribution range of the resources of the villages concerned. Natural pastures (rangelands) are the main fodder resources and sumplement feedings only account for less than 5% of the total fodder consumption. Crop cultivation and pastoral activities support each other to form a complete livelihood system. The ability of the farmig lands (crop cultivation) to provide the pastoral activities with concentrates and sumplements often becomes a main factor limiting the scale of livestock production at household level. Agropastoral transhumance is experiencing drastic changes in recent decades as is reflected in the size and composition of animals, the seasonal migration pattern, the relative importance of pastoralism in the household economy and the interplays of agricultural and pastoral elements of the system. In general, there is a decline in animal population and mobility, a shift in animal composition to meet new needs arising from changed macro-economic situation, a decrease in the relative importance in the household economy and an increasing decoupling of agro&pastoral relations. The fundamental divers of these changes can be traced to environmental, social, economic, technological and cultural changes from local to global levels and such changes have further caused local changes in livestock management objectives, land use and distribution of labor forces. Changes in local livelihood systems could have profound political, socioeconomic, cultural and ecological conseuquences. Agropastoral transhumance, as an age-old traditional livelihood strategy, is facing multifacet challenges, such as winter fodder shortage, rangeland degradation, lack of market competitiveness, decrease in economic importance, lack of appreciation among the young generation and adequate policies from the government. At the same time, economic globalization, market economy, intrdoctution of new technologies, increase of alternative income generating opportunities and the national re-oreitation of policies on mountain ecosystems have all brought about new opportunities for the transformation of the traditional livelihood system and the synchronized development of local society and the environment. Agropastoral transhumance interacts with the ecosystems at the timberline and treeline ecotone mainly through the following aspects: 1)Animal browsing and stamping affect the regeneration process of the forest communities and alters the composition and structure of the forest which in turn affect the succession process and vegetation pattern of the forest communities. Forest edges are the priority locations for summer houses and therefore the timeline and treeline area becomes the major venues of aninal activities; （2）herders create, maintain and improve pastures through burning that remove the forest communities at the timeline and treeline ecotone; 3）immediate grazing on the fire sites can significantly prevent the fire sites from perogressive succession; and 4）herders harvesting of construction timber and firewoods affects the structure and functions of the forest communities at the timberline and treeline zone. Timberline position in the survey region shows geographical variations. It is around 4200-4300m in Meilixueshan, Baimaxueshan and Jiawuxueshan in Northwest of Yunnan and rises to 4300-4400m in Yajiang County and Litang County of Sichuan. In Rangtang of Sichuan, it is between 4100-4200m, though reaching 4300m in localized sites. In the southern and eastern slopes of Gongga Mountain, the timberline is only between 3600m and 3700m and in Songpan County at the upper reach of the Minjiang River the timberline is around 3700-3800m.Treeline pattern follows similar trend. In many places, agropastoral transhumance and related human activities have lowered the timberline and treeline and narrowed or removed the treeline ecotone. In the area of survey, generally speaking, timberlines and treelines are lower on the southern slopes than on the northern slopes, with a difference between 20 and 200m. This is mainly because that the use of fires to crerate pastures has removed the forest vegetation at the previous timberline and above. In fact, in many places, well-preserved forests on the south slopes have even high timberline position that the corresponding northern slopes. At subalpine zone, grazing activities could have prohibited the natural regeneration of many forest fire sites and maintained the forest position at the present level. Grazing has a significant impact on the regernation process of forest communities at the timberline zone. Natural timberline and treeline ecotone has much higher density of treeline species individuals especially the emergents and seedlings than the timberlines that are maintained by human activities. In natural timberline and treelien ecotone without grazing interference, the density of the I Class seedlings (less than 10cm in height) ranges 725-2917 /hm2; while that in the treatment plots (with grazing disturbance) is only 0-228//hm2；II Class seedlings (10-50cm）exhibit similar density trends, reaching 550-5208//hm2 in natural timberline without grazing but only 14-321//hm2 in the plots with grazing treatment. In the man-created timberlines, there is no I Class seedling at all in plots with normal grazing activities. In relative terms, in plots without grazing activities, the propotion of I Class and II Class seedlings is much higher than that in plots with grazing. Grazing activities have significantly reduced the number of seedlings in the timberline ane treeline ecotone, and thus affect the natural regeneration process of the forests. Shrubs at the timberline and treeline ecotone can effectively protect the seedlings from severe climate and animal tramping, thus increasing the survival rate of the seedlings. Grazing following fires can completely inhibit forest regeneration process at timberline. Changes in agropastoral transhumance will have great impact on the timberline and treeline pattern of the studied area. The decrease in grazing intensity on alpine pastrues and the cessation of the use of fires will result an increase in the cover and height of shrubs above the present human-maintained treeline, which will create further condition for the expansion of timberline forest communities. Eastern Tibet Plateau harbors some most important mountain ecosystems of China that are of vital importance to the country’s strategy in biodiversity conservation, environmental construction and sustainable sociaoeconomic development. A proper knowledge of the interactions between traditional livelihood systems and the ecosystems in the region is a precondition to the realization of the above strategic goals. Therefore, the decision-makers must have a holistic and systemic perspective so as to integrate the multiple objectives of promoting sustainable socioeconomic development, conserving biological and cultural diversity and maintaining the balances among people, animal population and the ecosystems.

川西亚高山针叶林主要针叶树种年轮生态学研究

米亚罗地区是四川西部较为典型的亚高山针叶林区域之一。为建立该地区主要针叶树种岷江冷杉、云杉、紫果云杉和红杉的年轮宽度年表资料，了解不同海拔高度岷江冷杉原始林和不同恢复过程的人工针叶林及次生混交林树木径向生长规律，结合样地调查，用生长锥钻取了树木芯样做年轮生态学分析。芯样经过标准化程序固定和打磨抛光后，用WinDENDRO图像分析系统测量年轮宽度序列，用COFECHA程序交叉定年和控制测量数据质量，用ARSTAN程序建立了4个主要针叶树种的地区年表和不同海拔高度岷江冷杉林及人工针叶林和次生混交林针叶树的样地年表。 4个主要针叶树种年轮宽度年表的平均敏感度低于0.2，而其晚材宽度年表都具相对较高的平均敏感度。早材宽度与年轮总宽度标准化年表间的相关系数均在0.9以上；晚材宽度与年轮总宽度标准化年表间的相关系数则种间差异较大，红杉的最高，岷江冷杉的最低。岷江冷杉晚材宽度与年轮总宽度的相关性从1970年以后明显下降，而其他种的相关系数则随时间变化较小。树种之间标准化年表显著正相关，而云杉与紫果云杉和红杉与岷江冷杉之间相关系数明显较高。年表序列的第1主分量表达了4个树种树木共同径向生长变化格局；第2至第4主分量分别表达了云杉属和冷杉属、常绿针叶树种和落叶针叶树种以及云杉和紫果云杉树木径向生长变化差异。 不同海拔高度的8个岷江冷杉样地年轮宽度年表序列敏感度大体上随海拔高度升高而降低。各样地早材宽度与年轮总宽度年表之间的相关系数均在0.9以上，且随海拔高度变化不大；晚材宽度与年轮总宽度之间的相关系数随海拔高度的变化较大，并有随海拔升高而降低的趋势。样地年表序列之间相关系数差异很大，高海拔样地年表间多为显著正相关；低海拔样地年表间的相关系数变化不一；高海拔和低海拔样地年表之间相关性较差，且多不显著。样地年表的第1主分量能解释年表序列总方差的37.5%，反映了不同海拔高度岷江冷杉林木共同的径向生长变化格局；第2和第3主分量分别解释总方差的24.5%和18.2%，表现出明显的高海拔和低海拔样地树木间不同的径向生长变化，除一些样地例外，它们一般与低海拔样地年表有正相关，与高海拔样地年表有负相关。在那些另外的样地，海拔以外的其他因素可能也影响了树木径向生长变化。不同海拔高度样地林木的生长抑制和生长释放频率在不同时期表现出较大的差异，表明了不同的干扰历史和林木补充时间。 人工针叶林和次生混交林各样地林木早材宽度与其年轮总宽度年表之间相关系数均高达0.9以上；晚材宽度与年轮总宽度年表之间也都显著正相关，但人工针叶林样地的明显较高。样地年表序列之间的相关关系表现为，林分起源和经营管理相似的样地年表之间的相关系数明显较高，如人工针叶林与人工针叶林尽管树种不同，但样地年表之间显著正相关，而与次生混交林样地年表间关系不显著；反之亦然。综合比较各项生长参数及不同时期的树木径向生长速率，人工针叶林树木的胸径增长至少在40年以内是优于次生混交林的同种（或不同种）针叶树的。不同样地林木生长释放和生长抑制及人工针叶林树木胸高断面积增长分析表明，除严重的人为干扰外，林分郁闭后林木密度过大是造成高频率生长抑制的主要原因，在林分发育的适当时期通过抚育间伐等措施调控林分密度，是保证林木胸高断面积在一定时期内保持较高的连年增长的关键。日本落叶松作为引进的树种，在海拔3100 m左右种植表现良好，近30年来各项生长指标均高于林龄相近的云杉人工林，因此，适当用其作为川西亚高山针叶林采伐迹地快速恢复是合理的。 Miyaluo area is one of the typical regions covered by subalpine coniferous forests in western Sichuan province of southwestern China. To develop the regional tree-ring width chronology series for the dominant conifers such as Abies faxoniana, Picea asperata, P. purpurea and Larix potaninii, and to understand the radial growth patterns of conifers in Abies faxoniana natural forest stands at different altitudes, and in coniferous plantations and natural regenerated mixed stands in their different restoring processes as well, increment cores were sampled in the field together with conventional plots investigations for dendroecological analyses. After the increment cores being prepared according to standard procedures, the ring widths (total-ring and intra-ring widths) were measured with a WinDENDRO image-analysis system, and the measured tree-ring sequences were crossdated and quality-controlled with the software COFECHA. Using the software ARSTAN, we developed tree-ring width based chronology series of the four dominant conifers, eight site-specific Abies faxoniana chronologies, and seven site-specific chronologies of conifers in coniferous plantations and natural regenerated mixed stands. Mean sensitivities for total ring width chronologies of the four sampled dominant conifers were all below 0.2, while those for the latewood width chronologies of the same species were relatively much higher. Correlation coefficients between standard earlywood and total ring width chronologies of the four conifers were all above 0.9, but those between standard latewood and total ring width chronologies exhibited differences among species, with the coefficient of Larix potaninii the highest and that of Abies faxoniana the lowest. Correlation coefficients between latewood and total ring width of A. faxoniana obviously decreased from 1920-1970 for successive 50-year segments with 10-years lag analyses, though the same for the other three species changed unnoticeably with time. Tree-ring standard chronologies among species showed significant positive correlations, with the correlation coefficients between chronologies of Picea asperata and P. purpurea, and of Larix potaninii and Abies faxoniana relatively much higher. The first principal component of tree-ring chronologies represented the common radial growth patterns of the four conifers in Miyaluo area. The second, third and fourth PCs expressed the differences in radial growth responses for the genus Picea and Abies, for the evergreen and deciduous confers, and for the two species of the genus Picea, respectively. In general, mean sensitivities of the eight Abies faxoniana site-specific tree-ring width chronologies decreased with increasing altitude. The correlation coefficients between earlywood and total ring width chronologies for all sites reached 0.9, which did not change much with altitude; but those between latewood and total ring width chronologies diversified, with a decreasing tendency from lower altitudinal sites to higher altitudinal sites. Correlation coefficients among site chronologies varied considerably, with significant positive correlations among higher site chronologies, mixed results among lower site chronologies, and poor and insignificant correlations between chronologies of higher site and lower site. The first PC, which represents 37.5% of the total variance, reflected a common radial growth response at sites of different altitudes, and it showed a tendency of explaining more variance with increasing altitude. The second and the third PCs contributed to 24.5% and 18.2% of the total variance, respectively, exhibiting distinctive differences in radial growth responses between low- and high-altitudinal sites. With some exceptions, the radial growth represented by the second and third PCs had a positive correlation with that at the low-altitudinal sites and a negative correlation with that at the high-altitudinal sites. For those exceptional sites, factors other than altitude might also play a role in affecting tree-ring growth variations. Trees in stands of different altitudes showed great differences in frequencies of growth suppressions and releases through times, suggesting different disturbance histories and periods when trees recruiting to the canopy. Correlation coefficients between earlywood and total ring width chronologies for all sites of coniferous plantations and natural regenerated mixed stands were also above 0.9; and the same between latewood width and total ring width chronologies all positively correlated, too, with the coefficients of the coniferous plantations obviously much higher. Correlations among site chronologies showed that the coefficients among sites with similar stand origin and management regimes were much higher than those among sites with different stand origin and management regimes. For example, significant positive correlations were found for chronologies among different coniferous plantations, irrespective of species differences; while insignificant correlations between chronologies of the same conifer from a coniferous plantation and a natural regenerated mixed stand, and vise versa. Integrative comparisons of different tree growth parameters and radial growth rates at different stages indicated that the diameter at breast height (DBH) increments for trees in coniferous plantations were faster than those for trees of the same (or different) species in the natural regenerated mixed stands, at least within their first 40 years of stand development. Analyses of growth releases and suppressions, and basal area increments of trees in different stands demonstrated that over-dense individuals after canopy closure was the main factor resulting in high frequencies of radial growth suppressions, with some exceptions of severe man-made disturbances. Therefore, to ensure a continuous basal area current annual increment in certain periods, tree density controlling through thinning in due time during the stand development process are necessary. It should be mentioned that, as an introduced conifer to Miyaluo area, Larix kaempferi grew quite well at altitude of ca. 3100 m after planting in 1970s. In their near 30 years of stand development, Larix kaempferi trees exhibited faster growth in various parameters than Picea asperata trees of the similar stand age did. Thus we think it reasonable to use Larix kaempferi as a fast restoring species at appropriate sites of cutting blanks of subalpine coniferous forests in western Sichuan.