藏北高原典型植被样区物候变化及其对气候变化的响应

植被物候作为陆地生态系统对气候变化的响应和反馈的重要指示,已成为区域或全球生态环境领域研究的热点。基于非对称高斯拟合方法重建了2001—2010年MODIS EVI时间序列影像,利用动态阈值法提取藏北高原植被覆盖2001—2010年每年关键物候参数。选取研究区内东部高寒灌丛草甸、中部高寒草甸及西部高寒草原和高寒荒漠4种典型植被类型,并结合附近的4个气象台站气候资料,分析典型植被物候在近10a对关键气候因子的响应特征。研究结果表明:(1)4种不同典型植被的物候特征(EVImax降低、返青期延后和生长季长度缩短)均表现出高寒灌丛草甸→高寒草甸→高寒草原→高寒荒漠草原的过渡;(2)藏北高原近10a的年平均气温及春、夏、冬三个季度的平均气温均呈显著升高的趋势,升温幅度在0.8—3.9℃/10a,降水减少趋势不显著,在这种水热条件下典型植被均表现出返青提前(7.2—15.5d/10a)、生长季延长(8.4—19.2d/10a)的趋势,而枯黄出现时间为年际间自然波动;(3)高寒灌丛草甸EVImax主要受春季降水量和气温影响,且降水的影响程度大于气温;对高寒草甸植被而言,春、夏季的气温和降水均有较大的影响;而高寒草原和高寒荒漠草原主要受夏季平均气温和降水量影响;(4)高寒灌丛草甸的返青时间主要受前一年秋季降水量的影响,相关系数达-0.579;而高寒草甸、高寒草原和高寒荒漠草原主要受春季平均气温影响,高寒荒漠草原的特征最为明显(r=-0.559)。     

内蒙古主要草原类型植物物候对气候波动的响应

物候是气候变化的指示者,由于不同地区植被类型不同,导致其对气候波动的响应方式不同。利用2004—2013年内蒙古草原区生态监测站群落优势种物候观测资料和同时段的气象资料,分析了不同草原类型区优势种物候期变化及其与气候因子间的相互关系,结果表明:(1)2004—2013年内蒙古草原区各时段气候波动趋势均不显著,返青前以气温降低、降水增加趋势为主;黄枯前草甸草原、典型草原以气温降低、降水增加趋势为主,荒漠草原变化趋势相反。(2)2004—2013年典型草原植物返青期平均提前4.01 d,黄枯推后10.35 d,生长季延长14.36 d;草甸草原返青期提前2.04 d,黄枯期推后12.68 d,生长季延长14.72 d;荒漠草原物候变化趋势最小,返青期平均提前了1.32 d,黄枯期平均推后了9.58 d,生长季延长了10.90 d。(3)内蒙古草原区植物返青期主要受气温波动的影响,草甸草原返青期与前3个月平均气温的负相关最为显著,气温每升高1℃,返青期约提前1.123 d;典型草原、荒漠草原返青期与前2个月平均气温的负相关最为显著气,气温每升高1℃,返青期约提前1.137 d和1.743 d。(4)典型草原区植物黄枯期受前1—2月平均气温和累积降水的共同影响,与夏季平均气温和当月降水量的相关最为显著,夏季气温每升高1℃,黄枯期约提前2.250 d,当月降水每增加1 mm,黄枯期约推后0.119 d。草甸草原、荒漠草原植物黄枯期与各时段降水、气温的相关均不显著,影响黄枯机制比较复杂。     

东北地区植被物候时序变化

植被与气候的关系非常密切,植被物候可作为气候变化的指示器。东北地区位于我国最北部,是气候变化的敏感区域,研究该区植被物候对气候变化的响应对阐明陆地生态体统碳循环具有重要意义。利用GIMMS AVHRR遥感数据集得到了东北地区阔叶林、针叶林、草原和草甸4种植被25a(1982—2006年)的物候时序变化,得出4种植被春季物候都表现出先提前后推迟的现象,秋季物候的变化则比较复杂,阔叶林和针叶林整体上呈现出秋季物候推迟的趋势,草原和草甸则表现为提前-推迟-提前的趋势。应用偏最小二乘(Partial Least Squares)回归分析了该区域植被物候与气候因子之间的关系,结果表明:春季温度与阔叶林、针叶林和草甸春季物候负相关,前一年冬季温度与草原春季物候正相关,降水与植被春季物候的关系有点复杂;4种植被秋季物候与夏季温度均呈正相关,除草原外,其余3种植被秋季物候均与夏季降水负相关。植被春季物候可能主要受温度影响,而秋季物候很可能主要受降水控制。     

黄河上游玛曲县气候变化对植被的影响研究

利用1982年至2003年NASAGIMMS逐月归一化植被指数（NDVI）数据集和玛曲县气温、降水资料,对玛曲县近22年来NDVI变化和气候变化特征及其相互关系进行分析,以揭示黄河上游地区植被对全球变暖的区域响应.结果表明：（1）玛曲县植被变化在不同时段表现出较大差异,NDVI年际变化略有增加.（2）夏季是NDVI增长最快的季节,春季NDVI在20世纪90年代后期到本世纪初呈下降趋势,秋、冬季NDVI呈下降趋势.（3）返青期和NDVI值在春季达到同一水平值的时间及夏季达到峰值的时间逐年提前,说明生长季提前是该地区植被对全球变暖的主要响应表现.（4）玛曲县近22年来植被的NDVI变化在中等盖度水平（0.3～0.5）呈增加趋势,高盖度水平（≥0.7）的植被呈下降趋势,而在年代间变化水平上,气温和降水对植被生长都有影响,其中气温要比降水更显著;玛曲县降水和气温在季节尺度上对NDVI的影响不明显,除夏季气温与夏季NDVI关系密切之外,其他季节的关系均不明显.（5）按植被变化特点,将NDVI变化斜率最大值0.005定义为返青期指标,发现该地区牧草返青期的变化主要受温度条件影响,随气候变暖,返青期提前,其变化规律为4～5月份平均气温每10年升高0.6℃,返青期每10年提前3 d.     

中国草地和欧洲木本植物返青期对气温和降水变化的响应:基于生存分析的研究

长期以来,气候与植物物候关系的研究大多基于线性模型,但植被物候对气候变化的响应可能是非线性的。该文利用非线性模型——生存分析模型来分析时间序列中过去事件(气候因子)对目的变量(物候)的作用:用生存分析模型分析了春季气温和降水量对内蒙古草地、青藏高原草甸和欧洲地区木本植物返青期的影响。其中,内蒙古与青藏高原的物候信息来自遥感数据,欧洲地区物候信息为实测数据。蒙特卡洛方法用于拟合模型参数。结果表明:生存分析模型适合对上述不同研究对象的物候影响因素进行分析,并能模拟非线性效应;在内蒙古草地,春季气温和降水对春季返青有很大的影响,而青藏高原草甸和欧洲地区木本植物返青期对春季降水响应较小,对春季气温变化的响应随Holdridge干燥度指数上升而下降;在预测返青期时发现:春季平均气温提高1℃会导致上述地区返青期提前1–6天;而春季气温与降水的增加会导致返青期发生明显的非线性变化,这种非线性效应无法基于线性模型模拟出来。结果说明生存分析模型既能用于分析不同尺度下植物物候与气候的关系,也能用于模型预测,尤其适合探讨大幅度气候变化对物候的非线性影响。     

Responses of green-up dates of grasslands in China and woody plants in Europe to air temperature and precipitation: Empirical evidences based on survival analysis

长期以来, 气候与植物物候关系的研究大多基于线性模型, 但植被物候对气候变化的响应可能是非线性的。该文利用非线性模型——生存分析模型来分析时间序列中过去事件(气候因子)对目的变量(物候)的作用: 用生存分析模型分析了春季气温和降水量对内蒙古草地、青藏高原草甸和欧洲地区木本植物返青期的影响。其中, 内蒙古与青藏高原的物候信息来自遥感数据, 欧洲地区物候信息为实测数据。蒙特卡洛方法用于拟合模型参数。结果表明: 生存分析模型适合对上述不同研究对象的物候影响因素进行分析, 并能模拟非线性效应; 在内蒙古草地, 春季气温和降水对春季返青有很大的影响, 而青藏高原草甸和欧洲地区木本植物返青期对春季降水响应较小, 对春季气温变化的响应随Holdridge干燥度指数上升而下降; 在预测返青期时发现: 春季平均气温提高1 ℃会导致上述地区返青期提前1-6天; 而春季气温与降水的增加会导致返青期发生明显的非线性变化, 这种非线性效应无法基于线性模型模拟出来。结果说明生存分析模型既能用于分析不同尺度下植物物候与气候的关系, 也能用于模型预测, 尤其适合探讨大幅度气候变化对物候的非线性影响。     

东北地区植被物候对气候变化的响应

使用1982—2003年GIMMS-NDVI数据和气候数据,借助GIS空间分析和统计分析方法,分析了东北地区不同植被物候期与气候变化的关系。结果表明:22年东北地区年均温度以升高趋势为主,年降水量以减少趋势为主;针叶林、针阔叶混交林、阔叶林、草甸和沼泽植被生长季开始日期提前受春季温度升高影响显著(P<0.05)。春季降水对植被生长季开始日期变化影响较小,仅对针叶林生长季开始日期的推迟有显著的影响(P<0.05)。植被生长季结束日期受温度变化影响较小,仅草原植被生长季结束日期提前受秋季温度降低影响显著(P<0.05)。降水对东北地区植被生长季结束日期的变化影响高于温度。随着秋季降水量的减少,针阔叶混交林、草原和农田植被生长季结束日提前(P<0.05)。草丛生长季结束日期提前受夏季降水减少的影响显著(P<0.05);农田生长季结束日期提前亦受夏季和9月降水量减少的显著影响(P<0.05)。阔叶林和沼泽植被生长季延长受春季温度升高影响显著(P<0.05);灌丛植被生长季缩短受春季降水量减少影响显著(P<0.05);草丛和农田植被生长季延长受夏季降水量增加影响显著(P<0.05)。     

黄土高原植被物候变化及其对季节性气候变化的响应

受气候变化影响,全球范围内植被物候发生了显著变化,而目前针对不同植被分区类型下（荒漠草原区、典型草原区、森林草原区、落叶栎林区、落叶栎林亚区）植被物候变化及其对季节性气候变化响应的研究尚少。因此基于MODIS遥感归一化差值植被指数（MODIS NDVI：MOD13Q1）数据、中国植被区划数据及135个气象站点插值数据,利用Sen''s斜率估计、Hurst指数和高阶偏相关分析等方法,研究黄土高原2001-2018年植被物侯变化及其对季节性气候变化的响应。结果表明：（1）黄土高原植被生长季始期（SOS,Start of Growing Season）主要集中在第96-144天,子植被分区由西北向东南方向,逐渐呈现提前趋势,71.0%的像元植被SOS整体提前0-2 d/10a （α=0.05）,且在未来一段时间66%的像元植被SOS继续呈现提前趋势;植被生长季末期（EOS,End of Growing Season）主要集中在第288-304天,各子植被分区植被EOS变化基本保持一致,87.6％的像元植被EOS整体延迟0-3 d/10a （α=0.05）,且在未来一段时间有80%的像元植被EOS继续呈现推迟趋势。（2）黄土高原植被SOS主要受各季节温度的影响;当年春季降水导致植被SOS提前,主要分布在黄土高原中部;上年夏季和上年秋季降水增加会导致植被SOS推迟;当年春季、上年秋季和年初冬季的温度升高均会导致植被SOS提前;各子植被分区植被SOS对不同季节降水的响应存在差异,而对不同季节温度的响应具有一致性。（3）黄土高原植被EOS主要受各季节降水和秋季温度的影响;不同季节降水增加均会导致大部分植被EOS推迟;当年秋季温度导致整体区域植被EOS推迟,且各子植被区植被EOS对当年秋季温度响应具有一致性。该研究可为大尺度植被物候影响因素提供新的认识,也为植被适应未来气候变化提供借鉴。     

新疆天山山区禾本科牧草物候区域差异及其驱动力分析

天山山区地形复杂,同种植被因所处地理位置、地形特征的不同,其生育期对气候变化的响应特征差异明显。基于天山山区1990—2015年气象及物候观测数据,利用数理统计及空间插值等方法,分析了典型禾本科牧草物候空间差异及其关键驱动因子,结果表明:(1)26年来,天山山区年平均气温和年平均0 cm地温明显上升,北坡升温幅度大于南坡;年降水量增加,大致为"北坡趋多,南坡趋少";气候总体呈明显暖湿化趋势。(2)天山山区4个牧业气象观测站所共有的优势禾本科牧草物候呈现较明显的差异,春季返青期普遍提前,黄枯期大多为提前,生长季变化差异较大。(3)返青期主要受温度影响,与当月及春季平均气温、平均0 cm地温显著负相关,春季平均温度每升高1℃,返青日期提前1.98—5.77 d,春季平均0 cm地温每升高1℃,返青日期提前1.40—5.08 d;黄枯期主要受前期气温、0 cm地温和降水的综合影响,与前三个月的气温、0 cm地温显著负相关,与降水显著正相关。(4)在热量条件适合时,降水增加,对牧草的生育期是促进作用,相反,若热量条件不足时,降水增加,则会对牧草的发育产生抑制作用。(5)牧草生育期对于海拔高度的敏感性存在明显差异,随海拔高度的增加,物候对气候变化的响应程度更为显著。     

气候变化对内蒙古草原典型植物物候的影响

自然物候期是气候变化最直观的植物信号记录,自然物候变化是气候与自然环境变化的综合指标。基于1983—2009年内蒙古草甸草原、典型草原和荒漠草原区典型植物马兰草、霸王、贝加尔针茅和羊草生长期物候观测资料和同时段的气象观测资料,利用数理统计等方法,分析了不同草原区典型植物物候期与气候要素间的相互关系,结果表明:(1)1983—2009年内蒙古草原区植物物候期总体呈提前趋势,但地域差异明显,典型草原区植物萌芽返青、开花及黄枯期等物候提早趋势最为明显,说明不同草原区植物物候对气候变暖的区域响应不同。(2)内蒙古草原区植物物候期与气候变化密切相关。春季3—5月累积气温与植物萌芽返青期和开花期呈显著负相关,与日照时数为正相关,降水量对其影响不同草原区差异较大。荒漠草原和典型草原区植物黄枯期早晚与黄枯前1—2个月平均气温呈显著负相关,草甸草原区植物黄枯期与前1—2个月的降水量和日照时数有关,与气温关系不显著。(3)随着气候变暖,马兰草生长期缩短,霸王、贝加尔针茅和羊草生长期延长,其中典型草原区主要植物针茅生长季延长趋势最为明显,荒漠草原次之,草甸草原延长最少。     

Phenological responses to nitrogen and water addition are linked to plant growth patterns in a desert herbaceous community

Increases in nitrogen (N) deposition and variation in precipitation have been occurring in temperate deserts; however, little information is available regarding plant phenological responses to environmental cues and their relationships with plant growth pattern in desert ecosystems. In this study, plant phenology and growth of six annuals in response to N and water addition were monitored throughout two consecutive growing seasons in 2011 and 2012 in a temperate desert in northwestern China. The effects of N and water addition on reproductive phenology differed among plant species. N and water addition consistently advanced the flowering onset time and fruiting time of four spring ephemerals; however, their effects on two spring‐summer annuals were inconsistent, with advances being noted in one species and delays in another. N and water addition alone increased plant height, relative growth rate, leaf number, flower number, and individual biomass, while their combinative effects on plant growth and reproductive phenology were dependent on species. Multiple regression analysis showed that flowering onset time was negatively correlated with relative growth rate of two species, and negatively correlated with maximum plant height of the other four species. Our study demonstrates that phenological responses to increasing precipitation and N deposition varied in annuals with different life histories, whereby the effects of climate change on plant growth rate were related to reproductive phenology. Desert annuals that were able to accelerate growth rate under increasing soil resource availability tended to advance their flowering onset time to escape drought later in the growing season. This study promotes our understanding of the responses of temperate desert annuals to increasing precipitation and N deposition in this desert.     

内蒙古克氏针茅草原植物物候及其与气候因子关系

 植物物候作为气候变化敏感的生物圈指示计, 已经成为全球变化研究的热点。利用1985~2002年地面物候观测数据, 构建了内蒙古克氏针茅(Stipa krylovii)草原植物物候的时间序列谱, 并分析了植物物候的时间变异与气候因子之间的相关关系。结果表明: 1) 从1985~2002年内蒙古克氏针茅草原的气候朝着暖干趋势发展, 主要表现在春、夏气温的显著性增加与秋季(9月)降水的显著性减少; 2) 主要植物物候的变化整体呈返青期推后其它物候期提前趋势; 3) 植物生长盛期(7、8月)对气候变化最敏感; 4) 光照和温度是影响内蒙古克氏针茅草原植物物候格局的主要因素, 年内最寒冷的1月月均温和2、3月的光照对春季返青期具有负效应, 而其它物候期与7、8月的光照则呈显著的负相关关系, 6、7月的降水对发育盛期的花序形成、抽穗与开花具有显著的负效应, 8、9月的降水量能显著推后枯黄期的结束, 从而有利于生长季的延长。     

Consistent shifts in spring vegetation green‐up date across temperate biomes in China, 1982–2006

Understanding spring phenology changes in response to the rapid climate change at biome‐level is crucial for projecting regional ecosystem carbon exchange and climate–biosphere interactions. In this study, we assessed the long‐term changes and responses to changing climate of the spring phenology in six temperate biomes of China by analyzing the global inventory monitoring and modeling studies (GIMMS) NOAA/AVHRR Normalized Difference Vegetation Index (NDVI) and concurrent mean temperature and precipitation data for 1982–2006. Results show that the spring phenology trends in the six temperate biomes are not continuous throughout the 25 year period. The spring phenology in most areas of the six biomes showed obvious advancing trends (ranging from ?0.09 to ?0.65 day/yr) during the 1980s and early 1990s, but has subsequently suffered consistently delaying trends (ranging from 0.22 to 1.22 day/yr). Changes in spring (February–April) temperature are the dominating factor governing the pattern of spring vegetation phenology in the temperate biomes of China. The recently delayed spring phenology in these temperate biomes has been mainly triggered by the stalling or reversal of the warming trend in spring temperatures. Results in this study also reveal that precipitation during November–January can explain 16.1% (P < 0.05), 20.9% (P < 0.05) and 14.2% (P < 0.05) of the variations in temperate deciduous forest (TDF), temperate steppe (TS), temperate desert (TD) respectively, highlighting the important role of winter precipitation in regulating changes in the spring vegetation phenology of water–limited biomes.     

Spatial variations in aboveground net primary productivity along a climate gradient in Eurasian temperate grassland: effects of mean annual precipitation and its seasonal distribution

Concomitant changes of annual precipitation and its seasonal distribution within the context of global climate change have dramatic impacts on aboveground net primary productivity (ANPP) of grassland ecosystems. In this study, combining remote sensing products with in situ measurements of ANPP, we quantified the effects of mean annual precipitation (MAP) and precipitation seasonal distribution (PSD) on the spatial variations in ANPP along a climate gradient in Eurasian temperate grassland. Our results indicated that ANPP increased exponentially with MAP for the entire temperate grassland, but linearly for a specific grassland type, i.e. the desert steppe, typical steppe, and meadow steppe from arid to humid regions. The slope of the linear relationship appeared to be steeper in the more humid meadow steppe than that in the drier typical and desert steppes. PSD also had significant effect on the spatial variations in ANPP. It explained 39.4% of the spatial ANPP for the entire grassland investigated, being comparable with the explanatory power of MAP (40.0%). On the other hand, the relative contribution of PSD and MAP is grassland type specific. MAP exhibited a much stronger explanatory power than PSD for the desert steppe and the meadow steppe at the dry and wet end, respectively. However, PSD was the dominant factor affecting the spatial variation in ANPP for the median typical steppe. Our results imply that altered pattern of PSD due to climate change may be as important as the total amount in terms of effects on ANPP in Eurasian temperate grassland.     

1982—2015年中国温带不同草地植被枯黄期对极端气候事件的响应

随着极端气候事件频率和强度的增加,植被物候正在发生深刻的变化。然而,植被枯黄期(EGS)对极端气候的响应机制目前尚未厘清,特别是对于干旱半干旱地区的草地而言。因此,聚焦我国温带草地,基于1982—2015年全球监测与模型研究工作组归一化植被指数(GIMMS NDVI3g)长时间序列数据提取草地物候参数,并分析其时空变化规律;运用随机森林模型等方法探究温带草地EGS对极端气候变化的响应特征。结果表明：(1)全区多年平均EGS主要发生于270—290儒略日(DOY),59.8%的区域呈延迟趋势,其中显著延迟(P<0.05)的区域分布在新疆天山、阿尔泰山一带和准噶尔盆地西部、黄土高原北部、呼伦贝尔高原的西部和东北小兴安岭。(2)EGS与极端气温暖极值(日最低气温的最大值、日最高气温的最大值、暖夜日数、暖昼日数)之间均以广泛的正相关关系为主;相比之下,极端降水事件与EGS之间的关系相对比较复杂,这与各草地类型自身的生理策略和所处环境密切相关。(3)整体而言,持续干旱日数、气温日较差和暖夜日数对全域草地EGS动态变化具有极大的重要性。就不同草地类型而言,温带草甸草原主要受到气温日较差的影响...     

Alpine grassland plants grow earlier and faster but biomass remains unchanged over 35 years of climate change

Satellite data indicate significant advancement in alpine spring phenology over decades of climate warming, but corresponding field evidence is scarce. It is also unknown whether this advancement results from an earlier shift of phenological events, or enhancement of plant growth under unchanged phenological pattern. By analyzing a 35‐year dataset of seasonal biomass dynamics of a Tibetan alpine grassland, we show that climate change promoted both earlier phenology and faster growth, without changing annual biomass production. Biomass production increased in spring due to a warming‐induced earlier onset of plant growth, but decreased in autumn due mainly to increased water stress. Plants grew faster but the fast‐growing period shortened during the mid‐growing season. These findings provide the first in situ evidence of long‐term changes in growth patterns in alpine grassland plant communities, and suggest that earlier phenology and faster growth will jointly contribute to plant growth in a warming climate.     

Field evidence for earlier leaf-out dates in alpine grassland on the eastern Tibetan Plateau from 1990 to 2006

Worldwide, many plant species are experiencing an earlier onset of spring phenophases due to climate warming. Rapid recent temperature increases on the Tibetan Plateau (TP) have triggered changes in the spring phenology of the local vegetation. However, remote sensing studies of the land surface phenology have reached conflicting interpretations about green-up patterns observed on the TP since the mid-1990s. We investigated this issue using field phenological observations from 1990 to 2006, for 11 dominant plants on the TP at the levels of species, families (Gramineae—grasses and Cyperaceae—sedges) and vegetation communities (alpine meadow and alpine steppe). We found a significant trend of earlier leaf-out dates for one species (Koeleria cristata). The leaf-out dates of both Gramineae and Cyperaceae had advanced (the latter significantly, starting an average of 9 days later per year than the former), but the correlation between them was significant. The leaf-out dates of both vegetation communities also advanced, but the pattern was only significant in the alpine meadow. This study provides the first field evidence of advancement in spring leaf phenology on the TP and suggests that the phenology of the alpine steppe can differ from that of the alpine meadow. These findings will be useful for understanding ecosystem responses to climate change and for grassland management on the TP.     

民勤荒漠区16种植物物候持续日数及其积温变化

中国西北荒漠区植物物候随气温变暖表现为提前趋势。本文以甘肃民勤荒漠区16种植物34年的物候观测资料,采用一次趋势线方程研究了荒漠区植物在物候提前的过程中,物候日数变化和物候期积温变化。结果表明,随着气温升高,物候持续日数表现出一定的增长趋势。物候持续期积温增加显著,而且春、秋两季是积温变化较敏感的季节。积温的增减在很大程度上是由物候持续日数增加或减少引起的,其次才是由于气温增高引起的。表明,随着气温的增高或降低,植物的物候持续日数并不能无限制地缩短或延长。