Moving toward a new era of ecosystem science

Ecosystem is a fundamental organizational unit of the biosphere in which biological communities interact with their non-biological environment through energy flows and material cycles.Ecosystem science is the study of patterns,processes,and services of ecosystems.Since the 1990s,rising concerns regarding global climate change,biodiversity loss,ecosystem degradation,and sustainability of the human-dominated biosphere have stimulated the growth of ecosystem science,which is expected to provide systematic solutions to many of these major issues facing human societies.This paper provides a comprehensive review of the current progress in ecosystem science and identifies some key research challenges facing this discipline.We demonstrate that a key feature of the current progress in ecosystem science is its evolution from primarily theoretical explorations toward more systematic,integrative and application-oriented studies.Specifically,five major changes in the discipline over the past several decades can be identified.These include:(1)the expansion of the primary goal from understanding nature to include human activities;(2)the broadening of the research focus from single ecosystem types to macro-ecosystems comprising multiple regional ecosystems;(3)the shifting of research methods from small-scale observations and experiments to large-scale observations,network experiments,and model simulations;(4)the increasing attention to comprehensive integration of ecosystem components,processes,and scales;and(5)the shifting from a primarily biology-oriented focus to an integrated multi-disciplinary scientific field.While ecosystem science still faces many challenges in the future,these directional changes,along with the rapidly enriched research tools and data acquisition capabilities,lay a promising ground for the discipline’s future as a fundamental scientific basis for solving many environmental challenges facing human societies.

Sustainable wildlife protection on the Qingzang Plateau

Besides its ecological services to China and even Asia,the Qingzang Plateau(QP)hosts a rich variety of wildlife species.During the last century,wildlife population decreased quickly on the QP,driven by human interventions.Recently,wildlife has witnessed rapid recovery mainly propelled by a series of wildlife conservation policies.However,some cautions merit attentions to sustain wildlife restoration and conservation on the QP.This paper casted an overview of environmental and social-economic changes on the QP affecting wildlife subsistence.Re-sults show that QP has been warming,which can benefit wildlife recovery by easing extreme low temperature stresses.The fast growing social economy across the QP lays a solid economic foundation for investing on wildlife protection.Measures such as establishing conservation areas,constructing wildlife pathway corridors,and en-couraging herdsman moving out from wildlife rich regions,have boosted wildlife recovery.However,wildlife recovery is constrained by the limited carrying capacity of the ecosystem,left by domestic livestock.Additionally,fences intended to delineate conservation areas or to separate each type of grassland use,have brought about profound side effects on wildlife through fragmentation of their habitats.It is recommended to set up the fence in a more ecological way,which can be achieved by bypassing the wildlife frequent pathway and using mate-rials devoid of steel barb.Only considering both opportunities and problems simultaneously,can the wildlife protection on the QP be sustained.

Two Ultraviolet Radiation Datasets that Cover China

Ultraviolet（UV） radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization＇s measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes.

Carbon storage dynamics of subtropical forests estimated with multi-period forest inventories at a regional scale:the case of Jiangxi forests

Temperate and high-latitude forests are carbon sinks and play pivotal roles in offsetting greenhouse gas emissions of CO2.However,uncertainty still exists for subtropical forests,especially in monsoon-prevalent eastern Asia.Earlier studies have depended on remote sensing,ecosystem modeling,carbon fluxes,or single period forest surveys to estimate carbon sequestration capacities,and the results vary significantly.This study was designed to utilize multi-period forest survey data to explore spatial-dynamics of biomass storage in subtropical forests of China.Jiangxi province,a region with over 60%subtropical forest cover,was selected as the case study site and is located in central east China.Based on forest inventory data 1984-2013,and the stock-difference and biomass expansion factor methods,the carbon storage and density,of arboreal forests,economic forests,bamboo forests,woodlands and shrubberies were estimated.The results show that carbon storage increased from 159.1 Tg C in 1988 to 276.1 TgC in 2013,making up 3.1-3.8%of carbon stored throughout China.Among the four types of forests,the amount of carbon stored was as follows:arboreal forest>economic forest>bamboo forest>woodland and shrubbery.Arboreal forests accounted for 64.0-79.4%of the total.Forest carbon density increased from 21.2 Mg C ha-1 in 1984 to26.2 Mg C ha-1 in 2013,equal to 61.2-70.2%of the average carbon density of China’s forests in the same period.Forest carbon storage in Jiangxi will reach 355.5 Tg C and 535.8 Tg C in 2020 and 2030,respectively,and forest carbon density is predicted to be 31.9 Mg C ha-1and 46.4 Mg C ha-1,respectively.As one of the few studies using multi-period data tracking biomass dynamics in Jiangxi province,the findings of this study may be used as a reference for other research.Using Jiangxi as a case study underlies the fact that subtropical forests in China have great carbon sequestration potential and have fundamental significance to offset global environmental change effects.

青藏高原植被结构变化反映环境变迁

草地植被结构对于其生产和生态功能至关重要,但大尺度信息严重匮乏.本研究结合多源遥感数据和深度学习,在区域尺度上厘清了青藏高原高寒草地基于群系的植物群落结构空间格局,并比较了其历史变化.过去40年,高寒草甸在高寒草地中的比例从50%上升到69%,反映了变暖变湿的环境变化.此外,高寒草甸和高寒草原中高山嵩草草甸和紫花针茅草原的优势度分别增强到76%和92%.其中,气候因子驱动了紫花针茅草原近些年的分布;高山嵩草草甸近些年的分布则并非完全由气候驱动,人类活动可能起重要作用.本研究首次探索了区域尺度植被结构特征与历史变化,为认识青藏高原草地变化的驱动力及其空间异质性提供了新视角.

The spatial pattern of grassland aboveground biomass on Xizang Plateau and its climatic controls

Aims Grassland is the most widely distributed vegetation type on the Xizang Plateau.Accurate remote sensing estimation of the grass-land aboveground biomass(AGB)in this region is influenced by the types of vegetation indexes(VIs)used,the grain size(resolution)of the remote sensing data and the targeted ecosystem features.This study attempts to answer the following questions:(i)Which VI can most accurately reflect the grassland AGB distribution on the Xizang Plateau?(ii)How does the grain size of remote sensing imagery affect AGB reflection?(iii)What is the spatial distribution pattern of the grassland AGB on the plateau and its relationship with the climate?Methods We investigated 90 sample sites and measured site-specific AGBs using the harvest method for three grassland types(alpine meadow,alpine steppe and desert steppe).For each sample site,four VIs,namely,Normalized Difference VI(NDVI),Enhanced VI,Normalized Difference Water Index(NDWI)and Modified Soil-Adjusted VI(MSAVI)were extracted from the Moderate Resolution Imaging Spectroradiometer(MODIS)products with grain sizes of 250 m and 1 km.Linear regression models were employed to iden-tify the best estimator of the AGB for the entire grassland and the three individual grassland types.Paired Wilcoxon tests were applied to assess the grain size effect on the AGB estimation.General linear models were used to quantify the relationships between the spatial distribution of the grassland AGB and climatic factors.Important Findings The results showed that the best estimator for the entire grass-land AGB on the Xizang Plateau was MSAVI at a 250 m grain size(MSAVI_(250 m)).For each individual grassland type,the best estimator was MSAVI at a grain size of 250 m for alpine meadow,NDWI at a grain size of 1 km for alpine steppe and NDVI at a grain size of 1 km for desert steppe.The explanation ability of each VI for the grassland AGB did not significantly differ for the two grain sizes.Based on the best fit model(AGB=−10.80+139.13 MSAVI_(250 m)),the spatial pattern of the grassland AGB on the plateau was characterized.The AGB varied from 1 to 136 g m^(−2).Approximately 59%of total spatial variation in the AGB for the entire grassland was explained by the combination of the mean annual precipitation(MAP)and mean annual temperature.The explanatory power of MAP was weaker for each individual grassland type than that for the entire grassland.This study illustrated the high efficiency of the VIs derived from MODIS data in the grassland AGB estimation on the Xizang Plateau due to the vegetation homogeneity within a 1×1 km pixel in this region.Furthermore,MAP is a primary driver on the spatial variation of AGB at a regional scale.

Species turnover drives grassland community to phylogenetic clustering over long-term grazing disturbance

放牧通过改变草地群落物种组成和生物多样性,进而影响草地群落结构,对草地生态系统服务和功能产生深远的影响。然而,有关系统发育多样性和系统发育群落结构对长期放牧干扰的响应和适应的研究仍然很少,尤其是对于分布在极端环境中的生态系统。我们在青藏高原高寒草地上开展了多放牧强度的试验,探讨放牧干扰对植物系统发育多样性和群落结构的影响。研究发现,放牧干扰增加了植物群落的物种丰富度,促进了群落物种周转,从而改变了群落物种组成。低强度放牧对系统发育多样性和群落结构没有显著影响,而高强度放牧促使群落结构由分散向聚集变化。高强度放牧通过强烈的环境过滤作用,选择了一些耐牧的草地植物物种。在高强度放牧条件下,草地群落的聚集结构由近缘种的入侵和远缘种的丢失共同驱动。在植物功能性状水平上,我们发现与低强度放牧相比,高强度放牧通过改变根系深度对物种入侵产生影响,在很大程度上提升了物种的入侵性。我们的研究强调,仅仅利用物种丰富度和多样性并不能全面反映放牧干扰对草地群落的影响,而且在以后的放牧生态学研究中应该更加关注物种周转对群落系统发育多样性和群落结构的影响。

Current status and future directions of the Tibetan Plateau ecosystem research

The Tibetan Plateau (TP) encompasses Xizang and Qinghai and parts of northern Yunnan and Sichuan provinces, with a total area of circa 2.6 millions km2. The 2013 satellite data showed that grasslands, forests, wetlands, agricultural lands, and deserts account for 60%, 7.7%, 1.4%, 0.3%, and 30%, respectively, of total TP land (1)Due to its existence in dry, high altitude and cold environments, the TP ecosystem is extremely vulnerable to global climate change and studies on the TP ecosystem can be utilized as a pre-warning for other ecosystems.

干旱条件下蒸散变异由气象因子主控转变为生物因子主控

青藏高原被称为中国水塔,其蒸散(evapotranspiration,ET)影响着青藏高原的水分平衡及高寒草甸生态系统的稳定性。然而,全球变化进程对青藏高原蒸散的变异及其控制机制的影响尚不明晰。因此,本研究旨在明晰不同水分条件下,青藏高原高寒草甸生态系统蒸散变异受气象因子主控亦或是受生物因子主控。基于6年(2013-2018)的碳通量与气象因子和生物因子数据,采用线性扰动分析法量化了各气象因子和生物因子对蒸散变异的贡献。研究结果表明,在湿润年的生长旺季(7-8月),气象因子主控蒸散的变异。能量供应的不足限制了蒸散,因此净辐射和温度主控了蒸散的变异。在干旱年的生长旺季,蒸散变异由气象因子主控转变为生物因子主控,蒸散变异主要受到冠层导度和叶面积指数的控制。此时,生态系统受水分限制。本研究为深入研究不同水分条件下气象和生物因子如何控制蒸散变异提供了经验:有助于深刻理解水循环过程,可为未来气候变化条件下有效管理高寒草甸生态系统水资源提供理论基础。

Review on global change status and its impacts on the Tibetan Plateau environment

The Tibetan Plateau(TP)holds fundamental ecological and environmental significances to China and Asia.The TP also lies in the core zone of the belt and road initiative.To protect the TP environment,a comprehensive screening on current ecological research status is entailed.The teased out research gap can also be utilized as guidelines for the recently launched major research programs,i.e.the second TP scientific expedition and silk and belt road research plan.The findings showed that the TP has experienced significant temperature increase at a rate of 0.2℃ per decade since 1960s.The most robust warming trend was found in the northern plateau.Precipitation also exhibited an increasing trend but with high spatial heterogeneity.Changing climates have caused a series of environmental consequences,including lake area changes,glacier shrinkage,permafrost degradation and exacerbated desertification.The rising temperature is the main reason behind the glaciers shrinkage,snow melting,permafrost degradation and lake area changes on the TP and neighboring regions.The projected loss of glacial area on the plateau is estimated to be around 43%by 2070 and 75%by the end of the century.Vegetation was responsive to the changed environments,varied climates and intensified human activities by changing phenology and productivity.Future global change study should be more oriented toward integrating various research methods and tools,and synthesizing diverse subjects of water,vegetation,atmosphere and soil.

Lagged climatic effects on carbon fluxes over three grassland ecosystems in China

Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from three typical grassland ecosystems in China,including a temperate semiarid steppe in Inner mongolia(Neimeng site,Nm),an alpine shrub-meadow in Qinghai(Haibei site,Hb)and an alpine meadow steppe in Tibet(Dangxiong site,DX),to examine the time lagged effects of environmental factors on CO_(2) exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands.In linking carbon fluxes with climatic factors,we used their averages or cumulative values within each 12-month period and we called them‘yearly’statistics in this study.To investigate the lagged effects of the climatic factors on the car-bon fluxes,the climatic‘yearly’statistics were kept still and the‘yearly’statistics of the carbon fluxes were shifted backward 1 month at a time.Important Findingssoil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine Hb and DX,respectively,while the Nm site was under a synthetic impact of each climatic factor.The time lagged effect analysis showed that temperature had several months,even half a year lag effects on Co2 exchange at the three studied sites,while moisture’s effects were mostly exhibited as an immediate manner,except at Nm.In general,the lagged climatic effects were relatively weak for the alpine ecosystem.our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate,so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability.an improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.

Spatial sampling inconsistency leads to differences in phenological sensitivity to warming between natural and experiment sites

Plant spring phenology is receiving increasing attention owing to the recognition of its high sensitivity to ongoing climatic warming [1]. Changes in plant spring phenology can substantially influence a wide range of ecosystem structure and functions, which can not only affect human-beings but also in turn affect climate [2]. Warming experiments have been widely conducted to help understand, and thus predict plant phenological response to climate. Most of these experiment-based studies have focused on reporting the signs and magn让udes of phenological responses, and a few have included temperature sensitivity (phenological shifts per unit temperature change). However, applying the outputs of these experiments to predict future phenological response to climate change remains challenging.

青藏高寒草甸生态系统碳交换年际变异主要受生物效应影响

位于西藏的高寒草甸生态系统具有敏感脆弱的特点,在全球气候变化背景下,其碳汇功能的变化受到了广泛的关注。因此,本研究旨在明确高寒草甸碳通量的年际变异特征,并进一步量化各驱动因素对碳通量变异的贡献。本研究基于7年(2012-2018)的碳通量与气象因子和生物因子数据,采用一组查表法(look-uptables,,LUTs)对高寒草甸碳通量的年际变异来源进行了拆分和量化,并进一步利用线性扰动分析法量化了各个关键因子对碳通量变异的贡献。2012-2018年,高寒草甸生态系统净生产力(net ecosystem productivity,NEP)、总初级生产力(gross primary productivity,GPP)和生态系统呼吸(ecosystem respiration,Re)多年平均值分别为3.31±26.90、210.18±48.35和206.88±28.45gCm^(-2)y^(-1),表现出了较大的年际变异。本研究通过区分和量化气象因子和生物因子对碳通量年际变异的贡献,发现了生物因子对年际变异的主控作用。此外,发现了气象因子和生物因子之间的负反馈作用。在气象因子中,只有土壤水分对年际变异的贡献相对较大,并在气象因子和生物因子的相互作用中发挥着调节作用。这些结果表明,在气候变化背景下,若要准确估算碳通量,需考虑生物因子的作用。

Fisher判别法在识别干旱中的应用--以高寒草甸生态系统为例

Fisher判别法可综合考虑事物的多重属性特征,进而分辨事物类型。若能将其应用于对干旱的识别,或将成为一种准确而有效的干旱识别方法。本研究以高寒草甸生态系统为研究对象,基于9年碳通量和小气候观测数据,以土壤含水量(soil water content,SWC)和饱和水汽压差(vapor pressure deficit,VPD)作为判别因子,利用Fisher判别法识别干旱。Fisher判别法可用于对高寒草甸生态系统干旱的识别。因其综合考虑了土壤水分匮缺和大气水分匮缺,故可以更合理准确地判断干旱的开始和结束时间。基于干旱早样本和非干旱样本的特征,构建判别方程为:y=24.46SWC-4.60VPD。当y>1时,样本点位于临界线上方,若持续10天以上,则判定为发生干早。两次干早过程间隔2天以内,可认为是一次干旱过程。随着研究年限的增加和观测数据的积累,该临界线方程尚有优化空间,其对干旱识别的准确度可进一步提高。

Influences of drought on the stability of an alpine meadow ecosystem

Drought plays a prominent role in affecting ecosystem stability and ecosystem productivity.Based on eddy covariance and climatic observations during 2012-2020,the Fisher discriminant analysis method was employed to accurately detect drought occurrences.Furthermore,the ecosystem water sensitivity and its resistance to drought were quantified to evaluate the ecosystem stability.The results showed that the alpine meadow suffered drought most frequently at the beginning of the growing seasons.However,drought during the peak growing seasons reduced the gross primary productivity(GPP)the most,by 30.5±15.2%.In the middle of the peak growing seasons,the ecosystem water sensitivity was weak,and thus,the resistance to drought was strong,which resulted in high ecosystem stability.At the beginning and end of the peak growing seasons,the ecosystem stability was relatively weak.Ecosystem stability was positively related to the corresponding multiyear average soil water content(SWC_(ave)).However,drought occurring during high SWC_(ave)periods led to larger reductions in GPP,which indicated that the inhibitory effects of drought on ecosystems were more dependent on the occurrence time of droughts than on ecosystem stability.

Impacts of snow cover duration on vegetation spring phenology over the Tibetan Plateau

Aims Snow cover occupies large percentage of land surface in Tibetan Plateau.Snow cover duration(SCD)during non-growing seasons plays a critical role in regulating alpine vegetation’s phenology by affecting the energy budgets of land surface and soil moisture con-ditions.Different period’s snow cover during non-growing season may have distinct effect on the vegetation’s phenology.Start of season(SOS)has been observed advanced under the ongoing cli-mate change in the plateau,but it still remains unclear how the SCD alters the SOS.This study attempts to answer the following questions:(i)What is the pattern of spatial and temporal variations for SCD and grassland SOS?(ii)Which period’s SCD plays a critical role in grassland’s SOS?Methods The remote sensing datasets from the Moderate Resolution Imaging Spectroradiometer(MODIS)were utilized to compute the SOS and SCD on the Tibetan Plateau over 2003-2015.The Asymmetric Gaussian function was applied to extract SOS.We also explored the spatial pattern and temporal variation of SOS and SCD.Then,by using linear correlation coefficients,we investigated the driving effects of different period’s non-growing season SCD on SOS.Important Findings The non-growing season SCD slightly decreased during 2003-2015,while SOS exhibited an overall advancing trend.Advanced trends in SOS were observed in the eastern plateau,and the delayed trends were mainly founded in western plateau.Snow cover area exhibited two separate peaks during autumn and late winter over the plateau.Extended SCD regions mainly distributed in middle-east of the plateau,while shrunken SCD distributed in other regions of the plateau.SCD of different seasons caused distinct effects on vegetation SOS.Lengthened autumn SCD advanced SOS over the eastern plateau.The slightly lengthened SCD postponed SOS over the western plateau.In the wet meadow regions,advanced SOS was positively associated with SCD during the entire non-growing season,whereas for the dry steppe,SCD over the preseason played a more dominant role.The SCD of previous autumn and winter also showed lag effect on SOS over meadow regions to a certain extent.This study confirmed the importance of SCD to phenological pro-cesses at the beginning of growing season and further suggested that role of SCD should be discriminated for different periods and for dif-ferent heat-water conditions.With the lag effects and SCD’s distinct effect of different seasons considered,predictions on the Tibetan Plateau’s spring phenology could be improved.