Effective environmental factors in the distribution of vegetation types in Poshtkouh rangelands of Yazd Province (Iran)

The objective of this research was to study the relationships between environmental factors and vegetation in order to find the most effective factors in the separation of the vegetation types in Poshtkou rangelands of Yazd province. Sampling of soil and vegetation were performed with randomized-systematic method. Vegetation data including density and cover percentage were estimated quantitatively within each quadrat, and using the two-way indicator species analysis (TWINSPAN), and vegetation was classified into different groups. The topographic conditions were recorded in quadrat locations. Soil samples were taken in 0–30 and 30–60 cm depths in each quadrat. The measured soil variables included texture, lime, saturation moisture, gypsum, acidity (pH), electrical conductivity, sodium absorption ratio, and soluble ions (Na⁺, K⁺, Mg²⁺, Cl⁻, CO₃²⁻, HCO₃⁻ and SO₄²⁻). Multivariate techniques including principal component analysis (PCA) and canonical correspondence analysis (CCA) were used to analyse the collected data. The results showed that the vegetation distribution pattern was mainly related to soil characteristics such as salinity, texture, soluble potassium, gypsum, and lime. Totally, considering the habitat conditions, ecological needs and tolerance range each plant species has a significant relation with soil properties.     

Effect of sheep grazing on rangeland plant communities: Case study of landscape depressions within Syrian arid steppes

The arid rangelands of Syria cover over half of the nation's landmass. Punctuating this landscape are broad, dry basins, or wadis, and gentle landscape depressions that exhibit localized elevated vegetation productivity and unique edaphic and hydrologic properties. Historically, continuous heavy grazing and aggressive agricultural activities resulted in excessive ecological degradation within these sensitive environments. Information is needed to determine the influence of livestock grazing on plant communities in landscape depressions and the impact that this has on ecosystem resilience. The purpose of this research is to evaluate the effect of short-term sheep grazing on vegetation characteristics and plant community structure within depressions, and to provide recommendations for improved grazing management. Study plots were randomly located within paired topographic depressions located in northwestern Syria. Vegetation samples were collected along transects including plant biomass, plant density, herbaceous cover, and species diversity. In grazed plots, plant biomass was 49 g DM/m² compared to 234.4 g DM/m² in protected plots. Average plant density was 65 plants/m² in grazed plots compared to 1013 plants/m² in protected plots (P = 0.001). Herbaceous cover was 175% higher on protected sites compared to grazed plots. Average diversity (Shannon–Wiener index value) was 0.8 in grazed plots compared to 2.3 in protected plots. These results suggest that plant community structure will be impacted from short-term grazing and that a site's ability to positively respond to disturbance over time may be limited. We conclude that carefully planned grazing management should result in greater plant productivity and diversity.     

土壤盐分特征对内陆盐沼盐生植物群落的影响

为研究内陆盐沼植物群落的分布对土壤盐分的响应特征,选取鄂尔多斯盐湖盐沼区作为研究区,筛选了肉质耐盐植物群落,苔草植物群落和禾草植物群落3类典型植物群落,开展了土壤含水量、pH、电导率以及Na_⁺,K_⁺,Mg2_⁺,Ca_{^{2 +}},Cl_^-、SO_4^2-、CO_3^2-和HCO_3^-的测定,分析了区内典型植物群落对土壤水盐因子的响应规律。探讨了3类植物群落之间土壤因子含量的差异性;采用相关性分析和CCA分析,评价了3类植物群落多样性及物种分布随土壤因子的变化规律。结果表明,区内3类植物群落中,土壤盐分含量表现为肉质耐盐植物群落最高,苔草植物群落最低,禾草植物群落居中;植物多样性与土壤中含量最高的Na_⁺和SO_4^2-的相关性最显著;植物分布同时受到土壤盐分、水分和pH的显著影响。研究结果可为鄂尔多斯盐湖区土壤盐渍化改良和植被恢复提供理论支撑。     

The relation between accessibility,diversity and indigenous valuation of vegetation in the Bolivian Andes

A quantitative ethnobotanical study was conducted in the semi-arid Bolivian Andes community of Apillapampa to evaluate the impact of site accessibility on the diversity and perceived usefulness of (sub-)woody plants. Vegetation was sampled in thirty-six transects of 50 × 2 m², whereas data on plant uses were obtained from 13 local Quechua participants. Accessibility of sample sites correlated negatively with plant diversity, but positively with perceived usefulness. Hence, in spite of being less diverse, vegetation of more accessible sites was perceived as more useful to people than vegetation of more remote and also more diverse sites. This result contributes to the validity of the widely accepted notion that “more accessible plant resources are more useful to people”, not only at the level of individual plant species, but also for entire vegetation communities. In this respect, our finding that people attribute an equal usefulness to the vegetation of two local ecological zones (i.e. prepuna and puna) most likely reflects their similar accessibility from the village centre, which is located on the edge between both zones.     

Environmental factors controlling spatial variation in sediment yield in a central Andean mountain area

A large spatial variability in sediment yield was observed from small streams in the Ecuadorian Andes. The objective of this study was to analyze the environmental factors controlling these variations in sediment yield in the Paute basin, Ecuador. Sediment yield data were calculated based on sediment volumes accumulated behind checkdams for 37 small catchments. Mean annual specific sediment yield (SSY) shows a large spatial variability and ranges between 26 and 15,100 Mg km^− 2 year^− 1. Mean vegetation cover (C, fraction) in the catchment, i.e. the plant cover at or near the surface, exerts a first order control on sediment yield. The fractional vegetation cover alone explains 57% of the observed variance in ln(SSY). The negative exponential relation (SSY = a × e^{−b C}) which was found between vegetation cover and sediment yield at the catchment scale (10³–10⁹ m²), is very similar to the equations derived from splash, interrill and rill erosion experiments at the plot scale (1–10³ m²). This affirms the general character of an exponential decrease of sediment yield with increasing vegetation cover at a wide range of spatial scales, provided the distribution of cover can be considered to be essentially random. Lithology also significantly affects the sediment yield, and explains an additional 23% of the observed variance in ln(SSY). Based on these two catchment parameters, a multiple regression model was built. This empirical regression model already explains more than 75% of the total variance in the mean annual sediment yield. These results highlight the large potential of revegetation programs for controlling sediment yield. They show that a slight increase in the overall fractional vegetation cover of degraded land is likely to have a large effect on sediment production and delivery. Moreover, they point to the importance of detailed surface vegetation data for predicting and modeling sediment production rates.     

Relations between assemblages of carpological remains and modern vegetation in a shallow reservoir in southern Poland

This paper explores relations between assemblages of carpological remains and vegetation in and around a small, shallow reservoir in southern Poland. The study was conducted from 2006 to 2008. Quantity and distribution of species in the reservoir were recorded annually during the growing season. In October 2008, 40 samples of surface sediment (top 2?cm) were collected along transects at 10?m intervals. Samples of 100?cm³ were prepared for analysis of plant macroremains. Assemblages of carpological remains generally reflect local vegetation well. In some cases, however, even analysis of numerous samples failed to fully capture the species composition or reflect plant ratios in the parent phytocenosis. Reasons for this include factors that affect seed production, transport and fossilization, which differ among species. Among the best-represented macroremains were plants of the rush phytocenosis. In analysed samples, macroremains of 68.8?% of extant rushes were identified. Sixty percent of submerged and floating-leaf taxa were found in carpological samples, whereas 26.7?% of the trees and bushes were represented in sediment deposits. Species composition of phytocenoses in the reservoir and in surrounding areas was best reflected by macroremains from the nearby reed bed. Numbers of diaspores of Mentha aquatica, Hippuris vulgaris and Carex reflected well their relative abundance in phytocenoses. Chara sp., Juncus inflexus and Eupatorium cannabinum were overrepresented, whereas Typha latifolia and Sparganium minimum were poorly represented in relation to contemporary plant cover. There were no diaspores of Phragmites australis, which dominates the contemporary reed bed. Besides the shape of a reservoir, the key factor influencing diaspore numbers is distribution of plant cover. In many cases, single diaspores (Potentilla erecta, Myosotis scorpioides, Lythrum salicaria, Scutellaria galericulata), or higher concentrations (Hippuris vulgaris, Mentha aquatica, Eleocharis palustris, Schoenoplectus tabernaemontani, Chara sp.) reflected well the location of parent vegetation. The findings indicate that carpological remains in sediments can be an important source of information about plants in and around lakes. They generally reflect well local vegetation and in some cases may be used to identify taxa that dominated in the past.     

Spatial distribution and carbon stock of the Saxaul vegetation of the winter-cold deserts of Middle Asia

Carbon stocks and carbon accumulation in the earth's drylands have gained increasing attention. The winter-cold deserts of Middle Asia, i.e. in Kazakhstan, Uzbekistan, and Turkmenistan, cover an area of 2.5 million km². Within these deserts, the two Saxaul species White Saxaul (Haloxylon persicum Bunge ex Boiss. & Buhse) and Black Saxaul (Haloxylon aphyllum (Minkw.) Iljin) are dominant woody species with a potential distribution area of about 500,000 km². From the 1950s until today, the Saxaul vegetation has been degraded through logging and over-grazing. In this paper, we estimate the current and potential living above ground and below ground biomass of the Saxaul vegetation and its carbon stock. The living above ground biomass ranges between 1.5 t/ha and 3 t/ha. The potential carbon stocks above ground and below ground amount to 29.4–52.1 million t and 22–81.4 million t, respectively. Today, only 11%–28% of the potential biomass and carbon stock have remained. The carbon stock of the Saxaul vegetation is low compared to other ecosystems of the earth, but restoration and conservation of Saxaul vegetation is one way to sequester carbon through vegetation for Uzbekistan and Turkmenistan, which do not have much other woody vegetation.     

Analysis of vegetation seasonality in Sahelian environments using MODIS LAI,in association with land cover and rainfall

Present-day Sahelian vegetation in a highly anthropized semi-arid region is assessed from local to regional scales, through the joint analysis of MODIS LAI (1 km² and 8-day resolutions), daily rainfall, morphopedological and land cover datasets covering the period 2000–2008. The study area is located in northwest Senegal and consists of the “Niayes” and the northwestern “Peanut Basin” eco-regions, characterized by market gardening and rain-fed cultivated crops, respectively. The objectives are i) to analyse at pixel scale LAI time series and their relation to vegetation and soil types, ii) the estimation of phenological metrics (start of season SOS, end of season EOS, growing season length GSL) and their inter-annual variability, iii) to recognize the vegetation responses to rainfall trends (mean annual precipitation, MAP; frequency of rainy events, K; combination of MAP and K, called F).Pixel-scale analyses show that LAI time series 1) describe the actual phenology (agreeing with ground-truth AGHRYMET data), and thus can be used as a proxy for Sahelian vegetation dynamics, 2) are strongly dependent on soil types. Median maps of SOS and EOS suggest an increase of the GSL from Saint-Louis to Dakar, in agreement with both the North-South rainfall gradient and the intensification of agricultural practices around Dakar. Significant correlations (R: 0.64) between annual variation coefficient of LAI and MAP for both herbaceous crops and natural vegetation are highlighted; this correlation is reinforced (R: 0.7) using the rainfall distribution factors K and F. Rainfall thresholds allowing the SOS can be defined for each type of vegetation. These thresholds are estimated at 0–5 mm, 20 mm and 40 mm for natural herbs, herbaceous crops and shrublands, respectively.If previous works revealed the close link between the MAP and the SOS, our results highlight that LAI dynamics are also controlled by rainfall distribution during the Monsoon season. In this study, climatic indicators are proposed for estimating vegetation dynamics and monitoring SOS. Coupling Earth Observation data, such as MODIS LAI, with rainfall data, vegetation and soil information is found to be a reliable method for vegetation monitoring and for assessing the impact of human pressure on vegetation degradation.     

Vegetation and soil characteristics of the wasteland of Valika Chemical Industries near Manghopir, Karachi

The vegetation of the wasteland of Valika chemical industries near Manghopir road, Karachi was studied. Nine plant communities were recognized based on dominant species. In these plant communities the vegetation was disturbed, mostly halophytic and dominated bySuaeda fruticosa,Tamarix indica,Salsola baryosma,Cressa cretica,Atriplex griffithii,Haloxylon recurvum,Indigofera hochstetteri,Prosopis julifloraandChenopodium album.The physico-chemical properties of the soils were also analysed. Soil texture was mostly sandy loam, which exhibited slight variations in the water-holding capacity. The soils contained a sufficient amount of CaCO₃⁻and exhibited mostly alkaline soil pH. The soils of the different plant communities had scarcely any organic matter or inorganic phosphorus. The exchangeable sodium in the soils of many halophytic plant communities was high, with appreciable concentrations of potassium.     

民勤绿洲边缘物种多样性对水资源变化的响应

通过石羊河流域民勤绿洲边缘长期的生态定位观测和近年来对绿洲边缘的植被调查,计算植物种辛普森(Simpson)、香农威纳(Shannon-Wiener)多样性指数,分析物种多样性指数与地下水位下降趋势、年均降水量变化的相关性。结果表明:随地下水位的下降植物种类减少、物种多样性呈减低趋势;降水量与植物物种多样性具有较强的正相关关系。     

青藏高原东北部共和盆地末次冰消期以来古植被和环境演变(英文)

Paleoenvironmental history in the monsoonal margin in the northeast Tibetan Pla-teau provides important clue to the regional climate. Previous researches have been limited by either poor chronology or low resolution. Here we present a high-resolution pollen record from a 40.92-m-long sediment core (DLH) taken from Dalianhai, a terminal lake situated in the Gonghe Basin, the northeast Tibetan Plateau for reconstructing the vegetation and climate history since the last deglacial on the basis of a chronology controlled by 10 AMS 14C dates on plant remains preserved in the core sediments. The pollen assemblages in DLH core can be partitioned into 6 pollen zones and each zone is mainly characterized by the growth and decline of tree or herb pollen percentage. During the periods of 14.8-12.9 ka and 9.4-3.9 ka, the subalpine arboreal and local herbaceous pollen increased, indicating the subalpine forest developed in the surrounding mountains and a desert steppe or typical steppe developed in Gonghe Basin under a relatively moister climate. During the periods of 15.8-14.8 ka, 12.9-9.4 ka and 3.9-1.4 ka, the forest shrank or disappeared according to different degrees of aridity, and the desert steppe degraded to a more arid steppe desert in the basin, indicating a dry climate. After 1.4 ka, vegetation type around Dalianhai was mainly dominated by steppe suggested by increased Artemisia. Our results suggested the climate history in this region was dry from 15.8-14.8 ka, humid from 14.8-12.9 ka and dry from 12.9-9.4 ka, after which the climate was humid during 9.4-3.9 ka, followed by dry conditions during 3.9-1.4 ka and humid conditions in the last 1.4 ka. The change of pollen percentage and the evolution of palaeovegetation in Dalianhai since the last deglacial were similar to those recorded in Qinghai Lake. The forest expanded in the mountains around Dalianhai during the B?l-ling-Aller?d period, shrank during the Younger Dryas and the early Holocene, then it devel-oped and reached its maximum in the mid-Holocene. During the late Holocene, the vegetation began to shrink till disappearance. However, the timing of forest expansion in the Holocene lagged behind that of Qinghai Lake, and this spatial heterogeneity was probably caused by the different forest species between these two places. The maximum of forest development in the mid-Holocene was inconsistent with the period of stronger summer monsoon in the early Holocene indicated by stalagmite records, the reason might be related to the complexity of vegetation response to a large-scale climatic change.     

北方农牧交错区沙漠化的生物过程研究

通过对不同土地利用/覆盖下4种类型沙漠化土地的土壤与植被特征、变化规律、动因和互动关系的调查研究,结果表明土地沙漠化导致了土壤环境和植被的明显退化。其中严重沙漠化农田和非沙漠化农田相比,土壤有机质含量、速效氮、生长季土壤含水量分别下降66.2%、69.0%、74.8%,地温由21.5 ℃上升到22.4 ℃,其中干旱期严重沙漠化农田土壤含水量仅为23%,已无法满足作物生长需要。土壤环境恶化首先威胁土壤微生物和土壤动物的生存,使土壤微生物和动物数量分别下降95.0%和75.9%,酶活力下降39.5%~ 90.6%。同时植物多样性、种的饱和度和初级生产力大幅度下降,如严重沙漠化草地和非沙漠化草地相比,3项指标分别下降85.5%~883%,87.5%~ 950%和80.6%~ 967%,植被开始发生逆向演替,群落优势种不断更替,最终形成耐牧耐风沙的沙生植物群聚。旱作农田虽采取了施肥、中耕等管理措施,但光合转化效率和初级生产力还是下降了567%和574%。这一过程因其动因不同可分为植被退化(如放牧)引起的土地沙漠化和裸露地表风沙流活动直接导致的土地沙漠化(如农田风蚀和流沙迁移),前者是植被先行退化进而影响到土壤环境,其过程较为缓慢,后者是土壤环境首先恶化进而导致植。     

Paleoecology of The Southern Chilean Lake District-Isla Grande de Chiloé During Middle–late Llanquihue Glaciation and Deglaciation

Subantarctic Parkland and Subantarctic–North Patagonian Evergreen Forest, embracing >40,000 ¹⁴ C years of middle and late Llanquihue glaciation, are reconstructed from pollen contained in multiple interdrift deposits and cores of lake sediments. The subantarctic plant communities at low elevations have since been replaced by temperate Valdivian Evergreen Forest. Data in support of the vegetation reconstruction derive from close-interval sampling (>1400 pollen analysed stratigraphic levels) and high-resolution chronology (>200 AMS and conventional radiocarbon-dated horizons). Pollen sequences are from 15 sites, eight of which are exposures and seven mires, located in relation to lobes of piedmont glaciers that occupied Lago Llanquihue, Seno Reloncav', Golfo de Ancud, and the east-central sector of Isla Grande de Chiloí at the northern limit of the Golfo Corcovado lobe. Recurring episodes of grass maxima representing Subantarctic Parkland, when grass and scrub became widespread among patches of southern beech (Nothofagus), bear a relationship to glacial advances. The implication of the maxima, prominent with advances at 22,400 and 14,800 ¹⁴C yr BP during late Llanquihue glaciation in marine oxygen-isotope Stage 2, is of successive intervals of cold climate with summer temperatures estimated at 6–8°C below the modern mean. The earliest recorded maximum at >50,000 ¹⁴C yr BP is possibly during late Stage 4. At the time of middle Llanquihue glaciation in Stage 3, cool, humid interstades on Isla Grande de Chiloé with Subantarctic Evergreen Forest, which under progressive cooling after 47,000 ¹⁴C yr BP was increasingly replaced by parkland. During stepwise deglaciation, when transitional beech woodland communities supplanting parkland became diversified by formation of thermophilous North Patagonian Evergreen Forest, warming in the order of 5–6°C was abrupt after 14,000 ¹⁴C yr BP . Closed-canopy North Patagonian Evergreen Forest was established by 12,500 ¹⁴C yr BP . Later, after c. 12,000 until 10,000 ¹⁴C yr BP , depending on location, forest at low elevations became modified by expansion of a cold-tolerant element indicative of ≥2–3°C cooler climate. This stepwise climatic sequence is seen at all late-glacial sites. Cool, humid interstadial conditions, punctuated by cold stadial climate, are characteristic of the last ≥40,000 ¹⁴C years of the Pleistocene at midlatitude in the Southern Hemisphere. Pollen sequences from southern South America and terrestrial–marine records from the New Zealand–Tasmania sector express a broad measure of synchrony of vegetational/climatic change for marine oxygen-isotope Stages 2–3. The data, combined with the timing of glacial maxima in the Southern Andes, Southern Alps of New Zealand, and in the Northern Hemisphere, are indicative of synchronous, millennial-scale, midlatitude climatic changes in the polar hemispheres.     

Ecology and spatial patterns of large-scale vegetation units within the central Namib Desert

This article offers a review of published knowledge and a new state-of-the-art analysis regarding the floristic composition, the functional composition and the plant communities found in the central Namib Desert. At the same time, this paper contributes to the understanding of the relationship between the plant species composition of the central Namib Desert and the prevailing environmental gradients, with an emphasis on diversity and ecology in space and time. This article builds on three thematic foci. The first focus (1) lies on the present knowledge of the composition and the characteristics of the flora. A comprehensive floristic database has been compiled based on all available sources. A second focus (2) lies on the characterization and spatial distribution of the vegetation units. Therefore, we created a new vegetation classification based on a unique vegetation-plot database (http://www.givd.info/ID/AF-00-007) and additional data summing up to 2000 relevés, resulting in 21 large-scale vegetation classes. Using a supervised classification approach based on the vegetation classification, remote sensing and environmental data, we were able to produce a new vegetation map of the Central Namib. This was updated using expert knowledge, field visits and through manual preprocessing. With the third focus (3) we explore the spatial patterns of the previous foci and discuss their relation to environmental parameters and gradients.     

西藏高原地区陆地生态系统碳素循环平衡模拟

1IntroductionWith greatest concentration, carbon dioxide (CO2) is most sensitive to climate change among all the greenhouse gases. Since the Industrial Revolution, CO2 content emitted into the atmosphere has increased rapidly, due to the use of fossil fuels. According to estimations, CO2 concentration in the atmosphere has increased from 280 ppm in the early period of the Industrial Revolution (Melillo etal., 1995) to 368 ppm at present (Keeling and Whorf, 2000). It is universally accept…     

干旱地区植被影响沙地水分传输机理及其参数化

从植物生长与水分平衡的关系入手,在土壤水分动力学和近地面空气动力学等学科的研究基础上,依据植物生理生态学原理,探讨了干旱地区植被影响沙地水分传输的机理,初步建立了植被参数化模型和土壤-植物-大气连续体(SPAC)水分传输综合模型。主要研究结果如下:①分析了荒漠植物的生长及其动态变化特征,对沙生植物地上部与根系生长,尤其是根系在土壤中的分布进行了量化。②分析了荒漠植物的蒸腾特性及其气孔调节作用机制,指出了土壤水分亏缺是叶片气孔关闭、蒸腾作用降低的主要原因,探讨了植物蒸腾作用与气孔调节之间的复杂关系及其今后的研究重点。③揭示了沙地植被蒸发蒸腾的变化规律;分析了影响沙地植被蒸发蒸腾的生物因素和环境因素的作用。④初步建立了植被参数化和SPAC水分传输综合模型,模拟了植被结构影响冠层能量平衡过程,探讨了植物状态参数、生理参数与蒸发蒸腾的相互关系。     

Post-fire plant recovery in the Mojave and Sonoran Deserts of western North America

Increasing wildfire activity is one of the most pressing management concerns in arid lands of the American West. To examine post-fire recovery of perennial vegetation in the Mojave and Sonoran Deserts, I analyzed data systematically synthesized from the literature. Post-fire sprouting by desert perennials is generally limited but varies among species. For example, only 3–37% of Larrea tridentata sprouted compared to 64–86% of Yucca schidigera. Four of five studies measuring recovery of perennial cover reported close relationships (r² = 0.67–0.99) between time since fire (TSF) and cover. In fact, three studies measuring the longest TSF (≥37 years) found that cover had returned to within 10% cover of unburned areas within approximately 40 years. Conversely, post-fire species composition exhibited little convergence with unburned composition in five of six studies even 47 years after fire. Sphaeralcea ambigua, Gutierrezia spp., Achnatherum speciosum, Encelia spp., Hymenoclea salsola, and Baileya multiradiata had the highest burned:unburned abundance ratios, although overall post-fire community composition differed between the Mojave and Sonoran Deserts. Analyzing the literature as a whole suggested some generalities (e.g., that perennial cover reestablishes faster than composition), but more work is required for improving specific knowledge about plant recovery among fires, sites, species, and climates.     

Unexpected post-settlement freshening and increase in charophytes in Bombah Broadwater (Myall Lakes,New South Wales,Australia)

Bombah Broadwater is a shallow coastal lake within the Ramsar-listed Myall Lakes system on the mid-north coast of New South Wales, Australia. Increased nutrient and sediment loads resulting from catchment modification are thought to have instigated the loss of aquatic plants in the lake, causing it to “switch” from a clear, macrophyte dominated system (similar to the conditions in present day Myall Lake) to a turbid, phytoplankton dominated system. To assess this hypothesis, charophytes, foraminifera and aquatic fauna remains from an 800 year sediment record were examined. The sediment chronology was established using ¹⁴C, ²¹⁰Pb and ¹³⁷Cs radiometric dating and sediment composition. Interestingly, a clear increase in charophytes since European arrival conflicted with the hypothesised aquatic plant loss. Hence, it appears Bombah Broadwater has not undergone a change in stable state since European arrival. An additional and unexpected finding in the patterns of the foraminifera and testate amoeba suggest that Bombah Broadwater has freshened substantially since European arrival. This freshening may have resulted from increased catchment run off as a result of the clearance of catchment vegetation. Since catchment vegetation clearance is widespread in Australia, this finding raises the possibility that post-settlement freshening of coastal lakes may be a common occurrence.     

近5年青海省植被覆盖变化的遥感监测

This paper used five years （2001-2006） time series of MODIS NDVI images with a 1-km spatial resolution to produce a land cover map of Qinghai Province in China. A classification approach for different land cover types with special emphasis on vegetation, especially on sparse vegetation, was developed which synthesized Decision Tree Classification, Supervised Classification and Unsupervised Classification. The spatial distribution and dynamic change of vegetation cover in Qinghai from 2001 to 2006 were analyzed based on the land cover classification map and five grade elevation belts derived from Qinghai DEM. The result shows that vegetation cover in Qinghai in recent five years has been some improved and the area of vegetation was increased from 370,047 km^2 in 2001 to 374,576 km^2 in 2006. Meanwhile, vegetation cover ratio was increased by 0.63%. Vegetation cover ratio in high mountain belt is the largest （67.92%） among the five grade elevation belts in Qinghai Province. The second largest vegetation cover ratio is in middle mountain belt （61.80%）. Next, in the order of the decreasing vegetation cover ratio, the remaining grades are extreme high mountain belt （38.98%）, low mountain belt （25.55%） and flat region belt （15.46%）. The area of middle density grassland in high mountain belt is the biggest （94,003 km^2）, and vegetation cover ratio of dense grassland in middle mountain belt is the highest （32.62%）, and the increased area of dense grassland in high mountain belt is the greatest （1280 km^2）. In recent five years the conversion from sparse grass to middle density grass in high mountain belt has been the largest vegetation cover variation and the converted area is 15931 km^2.     

Effects of neighboring vascular plants on the abundance of bryophytes in different vegetation types

Due to the climate change, vegetation of tundra ecosystems is predicted to shift toward shrub and tree dominance, and this change may influence bryophytes. To estimate how changes in growing environment and the dominance of vascular plants influence bryophyte abundance, we compared the relationship of occurrence of bryophytes among other plant types in a five-year experiment of warming (T), fertilization (F) and T + F in two vegetation types, heath and meadow, in a subarctic–alpine ecosystem. We compared individual leaf area among shrub species to confirm that deciduous shrubs might cause severe shading effect. Effects of neighboring functional types on the performance of Hylocomium splendens was also analyzed.Results show that F and T + F treatments significantly influenced bryophyte abundance negatively. Under natural conditions, bryophytes in the heath site were negatively related to the abundance of shrubs and lichens and the relationship between lichens and bryophytes strengthened after the experimental period. After five years of experimental treatments in the meadow, a positive abundance relationship emerged between bryophytes and deciduous shrubs, evergreen shrubs and forbs. This relationship was not found in the heath site. Our study therefore shows that the abundance relationships between bryophytes and plants in two vegetation types within the same area can be different. Deciduous shrubs had larger leaf area than evergreen shrubs but did not show any shading effect on H. splendens.