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.

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.

青藏高原生态系统对气候变化的响应及其反馈

近几十年来,青藏高原正经历快速的气候变化,高原生态系统因此发生了深刻变化,并对周边地区产生了深远影响.本文围绕青藏高原生态系统结构和功能对气候变化的响应与反馈这一主线,系统总结了气候变化对物候、高山树线、生物多样性、植被生产力和生态系统碳汇功能的影响,阐述了青藏高原植被变化对区域气候的反馈及对亚洲季风的远程影响的研究进展.主要结论如下:气候变暖导致植被返青期总体提前,高原树线位置上升,高寒草原植物物种丰富度和多样性下降;气候变暖总体促进了高原植被生产力、增强了生态系统碳汇功能,但受限于土壤极大的空间异质性和对深层土壤碳动态理解的匮乏,目前对高原土壤碳库及土壤碳汇功能大小的估算仍具有较大不确定性.同时,青藏高原植被变化对近地表气温产生'负反馈'作用;植被活动增强还对东亚季风产生远程影响,导致我国东部夏季降水变化呈现'华南增加-长江黄河中间区域减少'的空间分异格局.未来的研究需要在完善观测体系基础上,加强对高寒生态系统对气候变暖的适应机理及生物地球物理反馈等过程的认知,为优化生态系统管理和保障青藏高原的生态安全提供理论基础.

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。

Grazing alters environmental control mechanisms of evapotranspiration in an alpine meadow of the tibetan Plateau

Aims Evapotranspiration(Et)is an important component of the terrestrial water cycle and is easily affected by external disturbances,such as climate change and grazing.Identifying Et responses to grazing is instructive for determining grazing activity and informative for understanding the water cycle.Methods this study utilized 2 years(2014 and 2017)of eddy covariance data to test how grazing regulated Et for an alpine meadow ecosystem on the tibetan Plateau(tP)by path analysis.Important Findings Radiation dominated Et with a decision coefficient of 64-74%.the soil water content(SWc)worked as the limiting factor in the fenced site.However,in the grazing site,the limiting factor was the vapor pressure deficit(VPD).Grazing had large effects on Et because it greatly affected the water conditions.the SWc and VPD were enhanced by 14.63%and 4.36%in the grazing site,respectively.therefore,sufficient water was supplied to Et,especially during drought,and strengthened the transpiration pull.As a result,a favorable micrometeorological environment was created for Et.Grazing shifted the limiting factor of Et from the SWc to VPD,which weakened the limiting effect of the water conditions on Et and advanced the Et peak time.In addition,grazing altered the compositions of Et by changing the community structure,which directly resulted in an increased Et.In summary,grazing enhanced Et through altering the community structure and micrometeorological environments.the findings of this study further improve our understanding of the driving mechanisms of grazing on Et and will improve our predictions for the global water cycle.

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.

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.