Effects of grazing exclusion on plant productivity and soil carbon,nitrogen storage in alpine meadows in northern Tibet,China

Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing exclusion on plant productivity, species diversity and soil organic carbon （SOC） and soil total nitrogen （STN） storage along a transect spanning from east to west of alpine meadows in northern Tibet, China. After six years of grazing exclusion, plant cover, aboveground biomass （AGB）, belowground biomass （BGB）, SOC and STN were increased, but species diversity indices declined. The enhancement of AGB and SOC caused by grazing exclusion was correlated positively with mean annual precipitation （MAP）. Grazing exclusion led to remarkable biomass increase of sedge species, especially Kobresia pygmaea, whereas decrease of biomass in forbs and no obvious change in grass, leguminous and noxious species. Root biomass was concentrated in the near surface layer （10 cm） after grazing exclusion. The effects of grazing exclusion on SOC storage were confined to shallow soil layer in sites with lower MAP. It is indicated that grazing exclusion is an effective measure to increase forage production and enhance soil carbon sequestration in the studied region. The effect is more efficient in sites with higher precipitation. However, the results revealed a tradeoff between vegetation restoration and ecological biodiversity. Therefore, carbon pools recover more quickly than plant biodiversity in the alpine meadows. We suggest that grazing exclusion should be combined with other measures to reconcile grassland restoration and biodiversitv conservation.     

Effect of snow-cover duration on plant species diversity of alpine meadows on the eastern Qinghai-Tibetan Plateau

Although snow cover plays an important role in structuring plant diversity in the alpine zone, there are few studies on the relationship between snow cover and species diversity of alpine meadows on the eastern Qinghai-Tibetan Plateau. To assess the effect of snow cover on plant species diversity of alpine meadows, we used ten parallel transects of 60 m × 1 m for this study and described the changes in species diversity and composition associated with snow depth. With the division of snow depth into six classes, the highest species richness （S） and species diversity （H′） occurred with an intermediate snow depth, i.e., class Ⅲ and class Ⅳ, showing a unimodal curve with the increase in snow depth. The relationship between snow depth and plant diversity （both richness and Shannon index） could be depicted by quadratic equations. There was no evident relationship between diversity （both S and H′） and soil water content, which implied that other more important factors influenced species diversity. The patterns of diversity found in our study were largely attributed to freeze-thaw alteration, length of growing season and disturbances of livestock grazing. Furthermore, snow depth affected species composition, as evaluated by the Sorensen＇s index of similarity. In addition, almost all species limited to one snow depth class were found only in class Ⅲand class Ⅳ, indicating that intermediate snow depth was suitable for the survival and growth of many alpine species.     

Biomass allocation patterns of alpine grassland species and functional groups along a precipitation gradient on the Northern Tibetan Plateau

Variations in the fractions of biomass allocated to functional components are widely considered as plant responses to resource availability for grassland plants. Observations indicated shoots isometrically relates to roots at the community level but allometrically at the species level in Tibetan alpine grasslands. These differences may result from the specific complementarity of functional groups between functional components, such as leaf, root, stem and reproductive organ. To test the component complementary responses to regional moisture variation, we conducted a multi-site transect survey to measure plant individual size and component biomass fractions of common species belonging to the functional groups： forbs, grasses, legumes and sedges on the Northern Tibetan Plateau in peak growing season in 2010. Along the mean annual precipitation （MAP） gradient, we sampled 7o species, in which 2o are in alpine meadows, 20 in alpine steppes, 15 in alpine desert-steppes and 15 in alpine deserts, respectively. Our results showed that the size of alpine plants is small with individual biomass mostly lower than 1.0 g. Plants keep relative conservative component individual responses moisture functional fractions across alpine grasslands at the level. However, the complementary between functional components to variations specifically differ among groups. These results indicate that functional group diversity may be an effective tool for scaling biomass allocation patterns from individual up to community level. Therefore, it is necessary andvaluable to perform intensive and systematic studies on identification and differentiation the influences of compositional changes in functional groups on ecosystem primary services and processes.     

The difference in pollen harvest between Apis mellifera and Apis cerana in a Tibetan alpine meadow

To explore the difference in pollen harvest between the western honey bee Apis mellifera and a native eastern honey bee A. cerana in the Zoige alpine meadows in the northeastern part of the QinghaiTibetan Plateau, we investigated species diversity of the harvested pollen and the amount of harvested pollen per bee for both species, and calculated the niche overlap(in terms of similarity in harvested pollen) between the two bee species during the flowering season from June to August 2016. Results showed that the species diversity of the harvested pollen was indistinguishable between the two bee species. Nevertheless, A. mellifera carried more(although not significant) pollens per bee than A.cerana. Moreover, pollen composition differed between the two bee species: A. mellifera mainly foraged on Anemone rivularis, Saussurea nigrescens and Anemone trullifolia, while A. cerana foraged on Anemone rivularis, Stellera chamaejasme, and Pedicularis longiflora. Consistently, the niche overlap between the two honeybee species was particularly small in several observations. Our results indicate a niche separation in pollen resource between the two honeybee species in a Tibetan alpine meadow.     

Impacts of warming on root biomass allocation in alpine steppe on the north Tibetan Plateau

Biomass is an important component of global carbon cycling and is vulnerable to climate change. Previous studies have mainly focused on the responses of aboveground biomass and phenology to warming, while studies of root architecture and of root biomass allocation between coarse and fine roots have been scarcely reported in grassland ecosystems. We conducted an open-top-chamber warming experiment to investigate the effect of potential warming on root biomass and root allocation in alpine steppe on the north Tibetan Plateau. The results showed that Stipa purpurea had significantly higher total root length, root surface area and tips than Carex moocroftii. However,there were no differences in total root volume, mean diameter and forks for the two species. Warming significantly increased total root biomass(27.60%), root biomass at 0–10 cm depth(27.84%) and coarse root biomass(diameter 0.20 mm, 57.68%) in the growing season(August). However, warming had no significant influence on root biomass in the non-growing season(April). Root biomass showed clear seasonalvariations: total root biomass, root biomass at 0–10 cm depth and coarse root biomass significantly increased in the growing season. The increase in total root biomass was due to the enhancement of root biomass at 0–10 cm depth, to which the increase of coarse root biomass made a great contribution. This research is of significance for understanding biomass allocation, carbon cycling and biological adaptability in alpine grassland ecosystems under future climate change.     

Species-area relationship within and across functional groups at alpine grasslands on the northern Tibetan Plateau,China

The species-area relationship(SAR) is one of the most fundamental concepts in community ecology and is helpful for biodiversity conservation.However,few studies have systematically addressed this topic for different alpine grassland types on the Tibetan Plateau,China.We explored whether the plant composition of different functional groups affects the manner in which species richness increases with increasing area at scales ≤ 1.0 m~2.We also compared species richness(S) within and across forbs,legumes,sedges and grasses,with sampling subplot area(A) increasing from 0.0625 m~2 to 1.0 m~2 between alpine meadow and steppe communities.We applied a logarithmic function(S = b_0 + b_1 ln A) to determine the slope and intercept of SAR curves within and across functional groups.The results showed that the logarithmic relationship holds true between species richness and sampling area at these small scales.Both the intercept and slope of the logarithmic forbs-area curves are significantly higher than those for the three other functional groups(P 0.05).Forb accounts for about 91.9 % of the variation in the intercept and 75.0% of the variation in the slope of the SAR curve when allfunctional groups' data were pooled together.Our results indicated that the different SAR patterns should be linked with species dispersal capabilities,environmental filtering,and life form composition within alpine grassland communities.Further studies on the relationship between species diversity and ecosystem functions should specify the differential responses of different functional groups to variations in climate and anthropogenic disturbances.     

Collecting <Emphasis Type="Italic">Ophiocordyceps sinensis</Emphasis>: an emerging livelihood strategy in the Garhwal,Indian Himalaya

In the Garhwal of Uttarakhand, India, the Bhotiya, an ethnically and culturally distinct tribal group, were historically engaged in seasonal migration (i.e. transhumance) to take advantage of scarce mountain resources and trade relations with Tibet. This livelihood practice has all but disappeared. Households are adapting to these changing circumstances by engaging in the collection and sale of the valuable alpine medicinal fungus Ophiocordyceps sinensis, widely known as Cordyceps. The collection of this fungus has exploded, emerging as a lucrative yet high-risk livelihood strategy for many Bhotiya communities. The Bhotiyas’ historic herding and trade-based interactions and knowledge of these alpine environments where Cordyceps are found uniquely positions them to access this valuable biological resource. Elsewhere in the Himalayan region, some households are earning as much as two-thirds of their income from the collection of Cordyceps; in China Cordyceps is now listed as an endangered species due to intense over-exploitation in the Tibetan Plateau. This paper seeks to fill the void in the scientific literature on the social, ecological and economic aspects of the emerging Cordyceps trade in the Garhwal. Our study investigates the socio-spatial dimensions of Cordyceps collection in the high alpine meadows. We document how a fusion of local knowledge and practice with alpine mountain systems has served to reinvigorate the economic integrity of mountain communities at a time of rapid socio-economic change and to reimagine a new relationship between alpine resources and community well-being. The article offers suggestions to address the sustainability of both Cordyceps collection and livelihood activities which hinge on this fungus population. We find a need for (1) community-based conservation measures that are rooted in (2) secure resource access rights for local communities to continue sustainable collection and sale of Cordyceps and (3) participatory-and science-based processes for determining appropriate local collection numbers.     

Clipping Alters the Response of Biomass Production to Experimental Warming: A Case Study in an Alpine Meadow on the Tibetan Plateau,China

Predicting how human activity will influence the response of alpine grasslands to future warming has many uncertainties.In this study, a field experiment with controlled warming and clipping was conducted in an alpine meadow at three elevations(4313 m, 4513 m and 4693 m) in Northern Tibet to test the hypothesis that clipping would alter warming effect on biomass production.Open top chambers(OTCs) were used to increase temperature since July,2008 and the OTCs increased air temperature by approximately 0.9o C ~ 1.8o C during the growing in2012.Clipping was conducted three times one year during growing season and the aboveground parts of all live plants were clipped to approximately 0.01 m in height using scissors since 2009.Gross primary production(GPP) was calculated from the Moderate-Resolution Imaging Spectroradiometer GPP algorithm and aboveground plant production was estimated using the surface-measured normalized difference vegetation index in 2012.Warming decreased the GPP, aboveground biomass(AGB) and aboveground net primary production(ANPP) at all three elevations when clipping was not applied.In contrast, warming increased AGB at all three elevations, GPP at the two lower elevations and ANPP at the two higher elevations when clipping was applied.These findings show that clipping reduced the negative effect of warming on GPP, AGB and ANPP, suggesting that clipping may reduce the effect of climate warming on GPP, AGB and ANPP in alpine meadows on the Tibetan Plateau, and therefore, may be a viable strategy for mitigating the effects of climate change on grazing and animal husbandry on the Tibetan Plateau.     

Aboveground biomass of the alpine shrub ecosystems in Three-River Source Region of the Tibetan Plateau

Though aboveground biomass (AGB) has an important contribution to the global carbon cycle, the information about storage and climatic effects of AGB is scare in Three-River Source Region (TRSR) shrub ecosystems. This study investigated AGB storage and its climatic controls in the TRSR alpine shrub ecosystems using data collected from 23 sites on the Tibetan Plateau from 2011 to 2013. We estimated the AGB storage (both shrub layer biomass and grass layer biomass) in the alpine shrubs as 37.49 Tg, with an average density of 1447.31 g m^-2. Biomass was primarily accumulated in the shrub layer, which accounted for 92% of AGB, while the grass layer accounted for only 8%. AGB significantly increased with the mean annual temperature (P < 0.05). The effects of the mean annual precipitation on AGB were not significant. These results suggest that temperature, rather than precipitation, has significantly effects on of aboveground vegetation growth in the TRSR alpine shrub ecosystems. The actual and potential increase in AGB density was different due to global warming varies among different regions of the TRSR. We conclude that long-term monitoring of dynamic changes is necessary to improve the accuracy estimations of potential AGB carbon sequestration across the TRSR alpine shrub ecosystems.     

Changes in leaf vein traits among vein types of alpine grassland plants on the Tibetan Plateau

Vein traits influence photosynthesis and drought resistance and are sensitive to climate change.It is unclear whether vein traits, similar to other leaf traits, have obvious regional characteristics and covariance with other leaf traits, especially in Tibetan Plateau grasslands. We collected 66 species from 37 sites in late July of 2012 and early August of 2013 to investigate leaf vein traits and their relationships with other leaf traits in comparison with the available global database data and to elucidate vein investment of plants with different vein types. The average vein length per area(VLA) of plants in the Tibetan Plateau was within the range of the global dataset, and the relationships among vein traits and other leaf traits of alpine plants were consistent with the global models.The VLAs of parallel-veined grasses and pinnateveined forbs were significantly lower and higher than the global mean value, respectively. The leaf mass perarea and total nitrogen content of parallel-veined grasses were significantly lower and higher,respectively, than the global mean values; the opposite was observed in pinnate-veined forbs. The parallel-veined grasses exhibited almost a four-fold higher vein biomass investment(i.e., vein mass per leaf mass) than pinnate-veined forbs in the same region. The average VLA and its relationships with other leaf traits of the alpine grassland plants on the Tibetan Plateau had no regional characteristics,suggesting a convergence in plant leaf functioning.Plants with different leaf types differ in their adaptation strategies to plateau environments, and this may relate to biomass investment into leaf veins.Our study fills the gap with regard to vein density in alpine grassland species and provides a new perspective for understanding plant physiology and ecology by calculating and comparing the proportion of vein investment among different vein types.     

Degradation induces changes in the soil C:N:P stoichiometry of alpine steppe on the Tibetan Plateau

Due to the Tibetan Plateau's unique high altitude and low temperature climate conditions,the region's alpine steppe ecosystem is highly fragile and is suffering from severe degradation under the stress of increasing population,overgrazing,and climate change.The soil stoichiometry,a crucial part of ecological stoichiometry,provides a fundamental approach for understanding ecosystem processes by examining the relative proportions and balance of the three elements.Understanding the impact of degradation on the soil stoichiometry is vital for conservation and management in the alpine steppe on the Tibetan Plateau.This study aims to examine the response of soil stoichiometry to degradation and explore the underlying biotic and abiotic mechanisms in the alpine steppe.We conducted a field survey in a sequent degraded alpine steppe with seven levels inNorthern Tibet.The plant species,aboveground biomass,and physical and chemical soil properties such as the moisture content,temperature,pH,compactness,total carbon(C),total nitrogen(N),and total phosphorus(P)were measured and recorded.The results showed that the contents of soil C/N,C/P,and N/P consistently decreased along intensifying degradation gradients.Using regression analysis and a structural equation model(SEM),we found that the C/N,C/P,and N/P ratios were positively affected by the soil compactness,soil moisture content and species richness of graminoids but negatively affected by soil pH and the proportion of aboveground biomass of forbs.The soil temperature had a negative effect on the C/N ratio but showed positive effect on the C/P and N/P ratios.The current study shows that degradation-induced changes in abiotic and biotic conditions such as soil warming and drying,which accelerated the soil organic carbon mineralization,as well as the increase in the proportion of forbs,whichwere difficult to decompose and input less organic carbon into soil,resulted in the decreases in soil C/N,C/P,and N/P contents to a great extent.Our results provide a sound basis for sustainable conservation and management of the alpine steppe.     

三江源区不同退化程度的高寒草甸光谱特征分析

 青海三江源区是长江、黄河、澜沧江3大河流的发源地。草地是该区域的主体生态系统,高寒草甸是其主要类型。近30年来,三江源地区草地发生了大面积的退化,不同退化程度的高寒草甸光谱特征是高寒草甸遥感分类和退化监测的重要依据。2009年8月作者在青海省三江源区对高山嵩草、矮嵩草和藏嵩草3种未退化高寒草甸,以及4种不同退化程度的高山嵩草草甸,进行了地面光谱测量和草地样方调查。同时对实测光谱曲线进行了比较,提取和分析了它们在557nm、675nm和760nm处反射率,以及"红边"斜率。结果表明,3种高寒草甸的光谱曲线,以及4种退化程度高寒草甸和未退化高寒草甸的光谱曲线在557nm处的反射率差异较小,在675nm和760nm处的反射率及"红边"斜率存在明显差异,能有效区分高寒草甸,可为高寒草甸遥感自动分类和退化监测提供依据。不同退化程度的高寒草甸地上生物量与其光谱曲线的"红边"斜率和归一化植被指数(NDVI)线性拟合的确定系数分别为0.93和0.87,其相关性较好,可用于高寒草甸地上生物量的估算。本文提取的光谱反射率的"红边"斜率不仅能有效区分3种典型高寒草甸和不同退化程度的高寒草甸,且与高寒草甸地上生物量的关系优于NDVI,对高寒草甸识别分类,退化监测和生物量估算有重要意义。     

Response of ecosystem respiration to experimental warming and clipping at daily time scale in an alpine meadow of tibet

The alpine meadow,as one of the typical vegetation types on the Tibetan Plateau,is one of the most sensitive terrestrial ecosystems to climate warming.However,how climate warming affects the carbon cycling of the alpine meadow on the Tibetan Plateau is not very clear.A field experiment under controlled experimental warming and clipping conditions was conducted in an alpine meadow on the Northern Tibetan Plateau since July 2008.Open top chambers(OTCs) were used to simulate climate warming.The main objective of this study was to examine the responses of ecosystem respiration(R eco) and its temperature sensitivity to experimental warming and clipping at daily time scale.Therefore,we measured R eco once or twice a month from July to September in 2010,from June to September in 2011 and from August to September in 2012.Air temperature dominated daily variation of Reco whether or not experimental warming and clipping were present.Air temperature was exponentially correlated with R eco and it could significantly explain 58～96% variation of R eco at daily time scale.Experimental warming and clipping decreased daily mean R eco by 5.8～37.7% and-11.9～23.0%,respectively,although not all these changes were significant.Experimental warming tended to decrease the temperature sensitivity of R eco,whereas clipping tended to increase the temperature sensitivity of R eco at daily time scale.Our findings suggest that R eco was mainly controlled by air temperature and may acclimate to climate warming due to its lower temperature sensitivity under experimental warming at daily time scale.     

Response of biomass spatial pattern of alpine vegetation to climate change in permafrost region of the Qinghai-Tibet Plateau,China

Alpine ecosystems in permafrost region are extremely sensitive to climate changes.To determine spatial pattern variations in alpine meadow and alpine steppe biomass dynamics in the permafrost region of the Qinghai-Tibet Plateau,China,calibrated with historical datasets of above-ground biomass production within the permafrost region's two main ecosystems,an ecosystem-biomass model was developed by employing empirical spatialdistribution models of the study region's precipitation,air temperature and soil temperature.This model was then successfully used to simulate the spatio-temporal variations in annual alpine ecosystem biomass production under climate change.For a 0.44°C decade-1 rise in air temperature,the model predicted that the biomasses of alpine meadow and alpine steppe remained roughly the same if annual precipitation increased by 8 mm per decade-1,but the biomasses were decreased by 2.7% and 2.4%,respectively if precipitation was constant.For a 2.2°C decade-1 rise in air temperature coupled with a 12 mm decade-1 rise in precipitation,the model predicted that the biomass of alpine meadow was unchanged or slightly increased,while that of alpine steppe was increased by 5.2%.However,in the absence of any rise in precipitation,the model predicted 6.8% and 4.6% declines in alpine meadow and alpine steppe biomasses,respectively.The response of alpine steppe biomass to the rising air temperatures and precipitation was significantly lesser and greater,respectively than that of alpine meadow biomass.A better understanding of the difference in alpine ecosystem biomass production under climate change is greatly significant with respect to the influence of climate change on the carbon and water cycles in the permafrost regions of the Qinghai-Tibet Plateau.     

Plant communities and factors responsible for vegetation pattern in an alpine area of the northwestern Himalaya

The study intended to describe the alpine vegetation of a protected area of the northwestern Himalaya and identify the important environmental variables responsible for species distribution. We placed random plots covering different habitats and altitude to record species composition and environmental variables. Vegetation was classified using hierarchical cluster analysis and vegetation-environment relationships were evaluated with Canonical Correspondence Analysis. Four communities, each in alpine shrub and meadows were delineated and well justified in the ordination plots. Indicator species for the different communities were identified. Maximum species richness and diversity were found in community IV among shrub communities and community II among the meadows. Studied environmental variables explained 61.5% variation in shrub vegetation and 59.8% variation in meadows. Soil variables explained higher variability (∼35%) than spatial variables (∼21%) in both shrubs and meadows. Altitude, among the spatial variables and carbon/nitrogen ratio and nitrogen among the soil variables explained maximum variation. About 40% variations left unexplained. Latitude and species diversity among the other variables had significant correlation with ordination axes. Study showed that altitude and C/N ratio played a significant role in species composition. Extensive sampling efforts and inclusion of other non-studied variables are also suggested for better understanding.     

Life strategy traits of the liana Sericostachys scandens spreading in the montane forests in the Kahuzi-Biega national park (DR Congo)

Sericostachys scandens is a monocarpic and heliophilous liana, native in tropical African forests. In the montane forests of the Kahuzi-Biega National Park (KBNP) (East of DR Congo), it has been expanding very strongly for a decade, and is currently considered as having negative impacts on biodiversity conservation. In this paper, we test if S. scandens differs from three co-occurring, native, non spreading lianas (Gouania longispicata, Tacazzea apiculata and Adenia bequaertii) for functional traits which might influence plant expansion. For leaf traits (SLA, dry matter content, nitrogen concentration), S. scandens did not show extreme values compared to those of the three other lianas. In contrast, S. scandens had much higher biomass allocation to sexual reproduction. It also differs from the three other lianas for its reproductive strategy that combines both vegetative propagation and sexual reproduction, and propagule dispersal by wind. Moreover, S. scandens has larger leaves and a greater number of lateral branches per unit stem length. It is argued that the particular combination of functional traits exhibited by S.scandens may in part explain its propensity to behave as an opportunistic weed in the disturbed areas in the montane forests of Kahuzi-Biega.     

Degradation stage effects on vegetation and soil properties interactions in alpine steppe

In recent decades,overgrazing and the warming and drying climate have resulted in significant degradation of alpine grasslands in the source region of the Yellow River.However,research into the relationships between vegetation and soil properties has mainly focused on an overall degradation stage,and few studies have investigated which soil properties can impact vegetation change at different stages of degradation.Vegetation and soil properties were observed in the field and measured in the laboratory for different predefined stages of degradation for alpine grassland in Maduo County in the source region of the Yellow River.Results show that:1)the aboveground and belowground biomass,soil organic carbon,total nitrogen,nitrate,and ammonia content did not decrease significantly from the intact to moderate degradation stage,but decreased significantly at severe and very severe stages of degradation;2)dominant plant species shifted from gramineaes and sedges to forbs;3)the species richness and Pielou evenness indices decreased significantly at the very severe degradation stage,the Shannon-Wiener diversity index increased at the slight and moderate degradation,but decreased at the severe and very severe degradation stages;4)soil bulk density was the strongest soil driver for changes in the plant biomass and community diversity at the intact,slight and moderate degradation stages,whereas soil organic carbon and nitrate nitrogen content were the main driving factors for changes in plant biomass and diversity at the severe and very severe degradation stages.Our results suggest that there may be different interactions between soil properties and plants before and after moderate stages of degradation.     

Phenological study of <Emphasis Type="Italic">Sargassum thunbergii</Emphasis> (Fucales,Phaeophyta) in Lidao Bay,Rongcheng, China

We conducted a phenological evaluation of Sargassum thunbergii, a common algal species, along the coast of Lidao Bay, Rongcheng, China. The local S. thunbergii population entered a maturation period from early June to mid-August, when seawater temperature was 14.4 to 25.1°C. Our results suggest an increase in temperature and day length during this period initiated thalli maturation. Inhabitants of the low tidal zone had higher thalli length and biomass compared with those from the mid-and high tidal zones. We observed a switch in the length frequency distribution and contribution of length classes to biomass between the small (<20 cm) and long (20–79.9 cm) length classes at the time of thallus maturity. This suggests there is a trade-offbetween sexual reproduction and vegetative regeneration.     

Allometric equations of select tree species of the Tibetan Plateau,China

The Tibetan forest is one of the most important national forest zones in China. Despite the potentially important role that Tibetan forest will play in the Earth?s future carbon balance and climate regulation, few allometric equations exist for accurately estimating biomass and carbon budgets of this forest. In the present study, allometric equations,both species-specific and generic, were developed relating component biomass(DW) to diameter at breast height(DBH) and tree height(H) for six most common tree species in Tibetan forest. The 6 species were Abies georgei Orr., Picea spinulosa(Griff.)Henry, Pinus densata Mast., Pinus yunnanensis Franch., Cypresses funebris Endl. and Quercus semecarpifilia Smith.. The results showed that, both DBH-only and DBH2 H based species-specific equations showed a significant fit(P0.05) for all tree species and biomass components. The DBH-only equations explained more than 80% variability of the component biomass and total biomass, adding H as a second independent variable increased the goodness of fit, while incorporating H into the term DBH2 H decreased the goodness of fit. However, not all DBH-H combined equations showed a significant fit(P0.05) for all tree species and biomass components. Hence, the suggested species-specific allometric equations for the six most common tree species are of the form ln(DW) = c + αln(DBH). The generalized equations of mixed coniferous component biomass against DBH, DBH2 H and DBH-H also showed a significant fit(P0.05) for all biomass components. However, due to significant species effect, the relative errors of the estimates were very high. Hence, generalized equations should only be used when there are too many different tree species, or there is no species-specific model of the same species or similar growth form in adjacent area.     

Rangeland privatization and its impacts on the Zoige wetlands on the Eastern Tibetan Plateau

The high Zoige Basin （Ruoergai Plateau） on the eastern Tibetan Plateau is a fault depression formed during intensive uplifting of the Tibetan Plateau. The wetland is globally important in biodiversity and is composed of marshes, bogs, fens, wet meadows and shallow water interspersed with low hills and sub-alpine meadows. Most of the Zoige wetlands have long been one of the most important grazing lands in China. Recent rangeland policy has allowed grazing, and usable wetland areas have been being legally allocated to individuals or groups of households on a long-term lease basis. Privatizafion of the wetland has impacted the Zoige wetlands in aspects of hydrologic condition, landscape and biodiversity. The uneven spatial distribution of water resources onprivatelands has led to the practice of extracting ground water, which has decreased the perched water table in Zoige. Fencing off the rangelands and grazing on expanding sand dunes have affected landscapes. Variation in the water table has led to the changes in vegetation diversity, resulting in the changes in wildlife and aquatic diversities and ecosystem processes. Making use all year round of the pasture that was previously grazed only in summer has shrunk the daily activity space of wildlife, and the newly erected fences blocked the movement of wild animals looking for food in the snow to lower and open areas. To maintain the favorable conditions of the Zoige wetland ecosystem, the author suggests that, in addition to biophysical research and implementation of conservation practices, there is an immediate need to initiate an integrated management program, increase public awareness of wetland functions and provide better training for the local conservation staff.