The influence of flood frequency, geomorphic setting and grazing on plant communities and plant biomass on a large dryland floodplain

Plant communities on semi-arid floodplains are ecologically important and support a diverse local and regional fauna and often pastoral economies. Water resource development may affect these communities and economies by decreasing water supply; determining the nature of these relationships is not straightforward because of the complex nature of plant responses to wetting and possible interactions with other drivers. We investigate the effects of reduced wetting on vegetation by examining spatial patterns in plant communities and above-ground herbaceous plant biomass across a flood frequency gradient, geomorphic settings and grazing exclosures. Community and biomass changes were also examined over time in relation to wetting events. The results demonstrate the importance of wetting on plant communities across timescales. At longer timescales, flood frequency influences community composition; at shorter timescales, wetting increase plant biomass and has a secondary influence on community composition. Plant biomass is also influenced in the short-term by grazing, but there is little influence of grazing on community composition. Soil nutrients do not vary systematically across the floodplain and have little influence on species distributions. We conclude that reduced water availability due to water resource development will result in reduced productivity in the short-term and community composition changes in the long-term.     

模拟增温和改变降雨频率对干旱半干旱区土壤呼吸的影响

温度和降水是干旱半干旱区土壤呼吸的重要扰动因子,全球气候变化导致的未来干旱半干旱区增温和降水变率增大对土壤呼吸有着重要影响。研究通过人工设置P_16×2.5mm、P_8×5mm、P_4×10mm、P_2×20mm、P_1×40mm的降雨频率梯度和增温2 ℃左右的控制试验,探讨不同降雨频率和增温处理对干旱半干旱区土壤呼吸的影响,以及土壤呼吸与土壤温湿度的关系及其对降雨频率改变的响应。结果表明：降雨频率和增温单独对土壤呼吸具有极显著影响（P<0.001）,但是两者之间并无交互作用（P>0.5）;在降雨量一定的情况下,土壤呼吸速率随着降雨频率的减小而减小,即多频率小降雨事件激发的土壤呼吸速率大于小频率大降雨事件;增温促进土壤呼吸,提高了约11%的土壤呼吸。本结果有助于对未来干旱半干旱地区全球变暖背景下降雨格局的改变对土壤呼吸产生的影响进行预测,同时也为进一步估算该区域生态系统的碳收支提供参考数据。     

Groundwater use by native plants in response to changes in precipitation in an intermountain basin

Many arid basins in western North America are likely to experience future changes in precipitation timing and amount. Where shallow water tables occur, plant acquisition of groundwater and soil water may be influenced by growing season precipitation. We conducted a rainfall manipulation experiment to investigate responses of four common native plant species to ambient, increased, and decreased summer monsoon rainfall. We measured plant xylem pressure potentials (Ψ) and stable oxygen isotope signatures (δ¹⁸O) to assess effects of altered precipitation on plant water relations and water acquisition patterns. Reduced rainfall decreased Ψ more in the grasses Sporobolus airoides and Distichlis spicata than the more deeply rooted shrubs Sarcobatus vermiculatus and Ericameria nauseosa. E. nauseosa had little response to natural or experimental differences in available soil water. Plant xylem water δ¹⁸O indicated that S. airoides and D. spicata are almost entirely dependent on rain-recharged soil water, while E. nauseosa is almost entirely groundwater-dependent. Sarcobatus vermiculatus used groundwater during dry periods, but utilized precipitation from soil layers after large rainfall events. Persistent changes in precipitation patterns could cause shifts in plant community composition that may alter basin-scale groundwater consumption by native plants, affecting water availability for human and ecosystem uses.     

黑河流域日降水格局及其时间变化

利用10个气象站1950—2000年日降水资料,对黑河流域的降水及其时空格局进行了研究。结果表明:①降水事件以≤5 mm的降水为主,占全年降水事件的82%,0～10 d间隔期占全年无降水期的40.7％,＞10 d间隔期占59.3％;②年降水日数与降水量之间存在显著的正相关性(r=0.78,P<0.01),＞10 mm降水总量与年降水量呈显著正相关,而≤5 mm降水总量与年降水量的相关性差;③＞10 mm和≤5 mm的降水总量变化范围分别为:0～262.6 mm,20.3～172.7 mm ,变异系数分别为0.25～0.92,0.17～0.25;④近50 d来,黑河流域近50 d降水量的变化总体上呈平稳上升趋势,≤5 mm的降水日呈现小幅下降的趋势,≥10 mm的降水日呈小幅上升的趋势。0～10 d的降水间隔期出现的频率总体保持不变,＞10 d间隔期出现的频率出现明显的下降趋势,年内总降水日数保持不变。     

1736年以来西安气候变化与农业收成的相关分析

基于清代雨雪与农业收成等档案记载及现代气象观测记录,根据西安冬季降雪与平均气温之间的统计关系、降水入渗与水量平衡模型,分别重建了西安1736~2000年冬季平均气温与4季降水序列,并分析了该地区气候变化特征及其对1736~2000年农业收成的影响。主要结论如下：(1) 西安的冷暖变化存在明显的百年际波动：其中18世纪相对温暖,19世纪寒冷,20世纪又转为温暖,且增暖趋势极为明显。(2) 西安的降水变化存在明显的年代际波动。自1736年以来,共经历了6个多雨期与7个少雨期,其中多雨期的平均雨量比少雨期多16%。(3) 气候变化对农业收成的影响极为明显。其中夏季降水量与秋收关系显著,而夏收又与前一年秋~当年春季的降水明显相关,且大多数严重歉收年均由降水明显偏少而致。虽然温度的年际变化与收成没有显著的联系,但温度年代际变化,即气候的冷暖阶段变化却与收成的阶段性变化关系密切。     

Effects of an exceptional drought on daily activity patterns, reproductive behaviour, and reproductive success of reintroduced Arabian oryx (Oryx leucoryx)

Activity patterns, social behaviour, and reproductive success of Arabian oryx were monitored in a reintroduced population in Mahazat as-Sayd Protected Area, Saudi Arabia. During the first year of the study, precipitation was 38% lower than the long-term average, whereas rainfall in the following year resulted in precipitation that was 92.8% of the long-term average. These dramatically different rainfall conditions corresponded with distinct patterns in various environmental parameters (air and soil temperature, humidity, wind speed, solar radiation, air pressure). Daily activity patterns, the frequency of social behaviours, and foraging activity were significantly reduced during the drought period. The frequency of reproductive behaviour was significantly related to daytime, air temperature and radiation, with a pronounced reduction of reproductive activities during the drought. Monthly rates of conceptions were considerably lower during the drought. Our results substantiate the idea that extended dry periods affect the population development of Oryx, but also raise questions about habitat suitability and carrying capacity. Future management of Arabian oryx should consider extreme climatic events as factors influencing various aspects of the ecology and behaviour of this species. This aspect may become even more important in the face of climate change, including a future increase of extreme climatic events.     

明代固原地区干旱灾害研究

通过对明代固原地区历史资料的搜集、整理、分析,对其干旱灾害等级化及成因等问题进行了研究。结果表明,固原地区自1368年到1644年间的277 a中,共发生干旱灾害118次,平均每2.35 a发生1次;其中轻度旱灾20次,占旱灾总数的16.9%;中度旱灾38次,占旱灾总数的32.3%;大旱灾42次,占旱灾总数的35.6%;特大旱灾18次,占旱灾总数的15.2%。该地区旱灾可分为4个阶段:第1阶段的1368-1424年和第3阶段的1505-1604年是旱灾的低发期;第2阶段的1425-1504年和第4阶段的1605-1644年是旱灾的高发期。该地区旱灾的季节性特征是单季旱占55.9%,其中夏旱所占比重最高,春旱、秋旱次之,冬旱较为稀少;季节性连旱占44.1%,其中春夏连旱和春夏秋3季连旱分别高达17.8%、15.3%。该地区明代处于气候的干冷期,年降水量减少是发生旱灾的主要原因。固原地区具有指示该时代气候变化特征的5次干旱气候事件,分别是明代的1437-1442年、1481-1490年、1608-1617年、1627-1634年、1637-1641年。     

Implications of local-scale productivity on compensatory growth in a semi-arid shrubland

Grazing is a dominant determinant of aboveground net primary production (ANPP) and composition of plant communities. However, ANPP can be maintained following grazing due to compensatory growth, the level of which might depend on additional environmental factors, such as precipitation and edaphic conditions. Several studies have shown that along large-scale regional gradients, community-level compensatory ability is positively correlated with ANPP and soil resource availability. However, community-level responses to grazing are also expected to be affected by local-scale heterogeneity in ANPP, particularly under low primary productivity typical to arid environments. Here, we studied the effect of local-scale variations in ANPP on the compensatory growth of an annual community in a semi-arid region. For two consecutive years, ANPP was evaluated following shoot damage in sites with different primary productivity. The results demonstrated that annual ANPP varied significantly among sites and among plots within sites; however, compensatory ability was negatively correlated with annual ANPP, with overcompensation in the least productive patches and under-compensation in the most productive patches. This pattern contradicts the positive correlation between ANPP and compensatory ability commonly found along large-scale productivity ecoclines, suggesting that the effects of ANPP on compensatory ability might be scale-dependent.     

基于标准化降水蒸散指数（SPEI）的毛乌素沙地1981—2020年干旱特征研究

大气干旱是影响半干旱沙区植被建设、生态恢复及社会经济可持续发展的重要因素。基于1981—2020年毛乌素沙地10个气象站点的逐月气象资料,计算了月、季和年尺度的标准化降水蒸散指数（SPEI）,分析了该沙区近40年降水和气温的变化趋势、干旱事件及其频率的时空特征。结果表明：（1）毛乌素沙地近40年降水量和气温均呈现显著的上升趋势（P<0.05）;秋季和冬季降水量呈现显著的上升趋势（P<0.05）,四季气温均呈现显著的上升趋势（P<0.05）。（2）毛乌素沙地总体上呈现出不显著的湿润化趋势（P>0.05）,但秋季呈显著的湿润化趋势（P<0.05）;中、西部地区呈现出湿润化趋势,而东部地区则呈现干旱化趋势。（3）近40年毛乌素沙地的月尺度下干旱总频率达32.71%,各等级发生频率为轻旱>中旱>重旱>特旱,季节发生频次为冬季>夏季、秋季>春季;轻旱主要发生在毛乌素沙地的北部、中部、东南和西南部,中旱在东部、北部和西部边缘,重旱在东部、中部以及南部地区,特旱在西北部、南部和东南部区域。     

民勤荒漠区几种主要固沙植物群落的水分平衡特性

 为了研究在自然状态下植物群落的自然稀疏密度、水分营养面积和耗水量等水分平衡特性,选择民勤荒漠几种典型植物群落,运用连续4 a的样方观测资料,分析了天然沙蒿、天然麻黄和人工梭梭林群落在自然降水条件下植物群落的自然稀疏密度、水分营养面积和耗水量等水分平衡特性。结果表明:天然沙蒿、天然麻黄和人工梭梭林群落在当地的自然稀疏密度相对稳定。群落中成年梭梭林的年耗水量与他人在同一地区用蒸渗仪且地下水位控制在1.4 m时测定的3 a幼苗的耗水量相当,梭梭密度较他人用降水量和蒸腾量、蒸发量推算的密度偏小。实验条件下单株植物的耗水量并不等于群落中个体的平均耗水量,在自然状态下研究得到的单株耗水量较在实验条件的下结论更为真实。植物蒸腾耗水量方面研究的真正有意义的是其在接近凋萎时的蒸腾耗水量,而不是特定供水条件下的几个特定值。     

科尔沁沙地降雨特征分析——以奈曼旗为例

了解降水的当前特征及未来的变化趋势对理解气候变化对区域生态系统的影响具有重要的意义。科尔沁沙地是中国北方农牧交错带的典型区域,年降雨量300~500 mm,对气候变化(特别是降水的变化)非常敏感。对科尔沁沙地沙漠化较为严重的奈曼旗1971-2013年的降水资料进行了分析研究。结果表明:(1)该地区多年平均降水量为338.8 mm,5-9月降雨量占全年降水量的(85.32±7.71)%,5-9月降雨量,年降水量1971-2000年经历了先增加后减少的趋势,2001-2013年有缓慢增加的趋势;同时降水量的年际变异性近10年也呈增加的趋势。(2)5-9月降雨量呈先增大后减小的趋势,在7月最大,为104.2 mm,5月和9月最小(分别为32.7 mm和32.8 mm),月降雨量的年际变率均大于49%;生长季内降雨主要以<10 mm的事件为主,占总降雨事件的64.41%,却仅占总降雨量的16.95%;≥30 mm的降雨事件占总降雨事件的10.96%,占到总降雨量的45.93%,且对总降雨量具有决定性的影响。(3)≥5 mm降雨的平均间隔为9.4 d,以1~10 d为主,占到69.5%,10~20 d(19.5%)的次之;≥30 d的发生频率最小,为3.81%,降雨间隔的年际变异性均呈增加的趋势。(4)生长季降雨日数呈减少的趋势,降雨事件降雨量的变异性与生长季降雨量的变化具有相似性,从2001年开始呈增加的趋势。该地区的降雨量年际变异性强,降雨日数的减少和降雨事件降雨量变异性的增加将提高极端干旱事件发生的频率,可能对该地区的生态系统产生严重影响,加剧该地区的沙漠化发展方向。因此,加强气候变化对生态系统影响的研究,可为合理利用土地资源及调整土地管理方式提供理论依据。     

1960—2017年太湖流域不同等级降水时空特征

基于太湖流域1960—2017年逐日降水数据,运用Mann-Kendall非参数检验法、R/S分析等方法,分析太湖流域不同等级降水的时空变化特征,并探讨了不同等级降水对年降水的影响。结果表明：1）近60年来,流域小雨发生率最高,为73.55%;年总降水量中,中雨量所占比例最大,为32.05%。小雨发生率呈显著减少趋势,暴雨贡献率呈显著增加趋势。2）太湖流域大雨、暴雨的降水量和降水日数都呈显著增加,小雨日数显著减少,小雨强度、年总降水强度显著增强。3）不同等级降水变化趋势的空间分布存在明显差异。小雨日数与年总降水日数,以及小雨强度与年总降水强度的变化趋势空间格局相一致。中雨日数、大雨日数、暴雨日数变化趋势的空间分布与其对应的降水量变化趋势的空间格局相似。4）R/S分析结果显示,小雨、暴雨、年总降水相关指标（小雨量除外）都表现出较强的持续性,未来变化趋势与过去相一致。5）近60年来,太湖流域年总降水量、降水日数、年总降水强度的变化,分别受中雨量、小雨日数、暴雨量的影响较大。在旱年流域年降水量偏少受大雨量减少的影响较大,而涝年年降水量偏多受暴雨增加的影响较大。     

华北平原降水的长期趋势分析(英文)

The North China Plain (NCP) is the most important food grain producing area in China and has suffered from serious water shortages. To capture variation water availability, it is necessary to have an analysis of changing trends in precipitation. This study, based on daily precipitation data from 47 representative stations in NCP records passed the homogeneity test, analyzed the trend and amplitude of variation in monthly, seasonal and annual precipitation, annual maximum continuous no-rain days, annual rain days, rainfall intensity, and rainfall extremes from 1960 to 2007, using the MannKendall (M-K) test and Sen’s slope estimator. It was found that monthly precipitation in winter had a significant increasing trend in most parts, while monthly precipitation in July to September showed a decreasing trend in some parts of NCP. No significant changing trend was found for the annual, dry and wet season precipitation and rainfall extremes in the majority of NCP.A significant decreasing trend was detected for the maximum no-rain duration and annual rain days in the major part of NCP. It was concluded that the changing trend of precipitation in NCP had an apparent seasonal and regional pattern, i.e., precipitation showed an obvious increasing trend in winter, but a decreasing trend in the rainy season (July to September), and the changing trend was more apparent in the northern part than in the southern and middle parts. This implies that with global warming, seasonal variation of precipitation in NCP tends to decline with an increasing of precipitation in winter season, and a decreasing in rainy season, particularly in the sub-humid northern part.     

Livestock responses to droughts and severe winter weather in the Gobi Three Beauty National Park, Mongolia

We investigated how both droughts and dzuds (severe winter weather) control livestock mortality in a non-equilibrium steppe ecosystem of Mongolia, Gobi Three Beauty National Park. These steppe ecosystems have developed under high interannual variability of rainfall and nomadic grazing systems. Interannual precipitation variation was 39%, with 128 mm mean annual precipitation. The effect of climate variability and extreme events on livestock mortality is a critical aspect for the Mongolian economy. Analysis of drought and precipitation variability on livestock mortality rate was not significantly influenced by the index of mean annual precipitation and annual winter temperature. Overall, unlike hot dry regions, pastoral livestock mortality in the cold dry regions was affected more by dzuds and annual growing seasonal rain than by droughts. Dzuds can be frequent events, occurring as often as once every 2 and 3 years within a decade. The average annual livestock mortality for the combined drought and dzuds years (18%) was 4.8% greater than the years with dzuds alone, and 7% greater than in years with only drought. Thus livestock mortality appears to be more sensitive to dzuds than to droughts, and that dzuds contributes more to livestock mortality even years where combined drought and winter storms occur.     

荒漠草原植物群落光合速率对水氮添加的响应

氮沉降和降水格局改变对草原生态系统的结构、功能及关键过程具有重要影响。依托内蒙古乌拉特荒漠草原研究站的全球变化实验平台,研究了氮添加和增减雨（+50%、-50%）及其交互作用对荒漠草原植物群落光合速率和植被特征的影响,分析了荒漠草原植物群落光合速率与植被特征的关系。结果表明：（1）短期氮添加对荒漠草原植物群落光合速率和植被特征没有显著影响（P > 0.05）;（2）降水格局改变显著影响荒漠植物群落光合速率（P < 0.05）,减雨50%显著降低了荒漠草原植物群落光合速率和优势种植物高度（P < 0.05）,而降水增加50%没有改变群落光合速率和植被特征,降水改变下的土壤水分能很好地解释群落光合速率;（3）氮添加和增加降水的交互效应显著提高了群落的光合速率和优势种植物高度（P < 0.05）,而减少降水与氮添加没有显著影响;（4）荒漠草原植物群落盖度、优势种盖度、优势种平均高度与群落的光合速率呈现出指数增加关系,解释率为40%~58%。干旱极大地抑制荒漠草原植物群落光合速率,而氮沉降则依赖于降水增加来提高群落的光合速率,荒漠草原植物群落光合速率与水肥处理下的植物生长特征具有密切的关系。     

The effects of precipitation timing on sagebrush steppe vegetation

Changes in precipitation patterns and inputs have the potential to cause major changes in productivity, composition, and diversity of terrestrial plant communities. Vegetation response to altered timing of precipitation was assessed during a 7-year experiment in an Artemisia tridentata spp. wyomingensis community in the northern Great Basin, USA. Four permanent rainout shelters excluded natural rainfall, with seasonal distribution of precipitation controlled with the use of an overhead sprinkler system. Precipitation treatments under each shelter were WINTER, SPRING, and CURRENT. The WINTER treatment received 80% of its water between October and March; in the SPRING treatment 80% of total water was applied between April and July; and the CURRENT treatment received precipitation matching the site's long-term (50 years) distribution pattern. A CONTROL treatment, placed outside each shelter replicate, received natural precipitation inputs. CURRENT, WINTER, and CONTROL treatments had similar in soil water-content patterns and thus, there were few consistent differences in vegetation response. The SPRING treatment resulted in more bare-ground and lower plant productivity compared to other shelter treatments. This result contrasted with our initial hypothesis that shallower-rooted grasses would gain a competitive advantage over shrubs if precipitation was shifted from winter to spring. Our results also demonstrated the resilience of these communities to climate perturbation as many of the vegetation shifts did not begin until the fourth year after treatments were applied.     

RDI指数在新疆5个地区干旱监测的应用

为加强新疆地区干旱动态监测与评估,基于阿勒泰、伊宁、乌鲁木齐、和田、哈密5个气象站近49 a的逐日降水与蒸散数据,采用计算简单、敏感性与稳定性较强的RDI指数分析了5个地区季尺度以及年尺度的干旱特征,并指出了未来新疆地区干旱评估的发展方向。结果表明：（1） 5个地区在年尺度和4个季尺度上的干旱强度与频率略有差异,但干旱程度均有所下降,都存在湿润化趋势,乌鲁木齐湿润化程度最高,和田地区湿润化程度最低。（2） 从季节上看,阿勒泰地区夏、秋两季湿润化程度较高,春、冬两季湿润化程度较低;伊宁和乌鲁木齐两地夏、冬两季湿润化较明显,春、秋两季湿润化程度较低;和田、哈密两地春、夏、秋三季都比冬季湿润化程度高。     

新疆极端降水的气候变化

采用1961～2000年55个气象台站的逐日降水观测资料,分析近40年来新疆极端降水的气候变化、发展趋势和空间分布差异。用Mann-Kendall法对年极端降水量进行突变检验。研究表明：(1) 只有天山北麓经济带和天山南麓国家级棉花基地阿克苏地区极端降水量和频次有显著增多,尤以80年代以后明显,年极端降水量于1980年发生了气候突变,这种气候变化是由夏半年极端降雨量和频次增多导致的。(2) 新疆极端降水强度无显著变化,极端降水频次的显著增多导致极端降水量的显著增多。(3) 极端降水对年总降水量的贡献天山山区占年降水量的41.9%,北疆北部与和田区域极端降水的贡献为17.2%和21.9%,其它区域在25%~31.3%。年极端降水量距平与年降水量距平有好的相关关系 (除阿克苏地区和焉耆盆地外),说明极端降水量的变化导致年降水量的变化。     

基于标准化流量指数(SDI)的石羊河流域水文干旱特征

利用石羊河流域8个水文站1961－2017年逐月实测流量数据和4个气象站点的气象观测资料,采用标准化流量指数（SDI）、游程理论来获得干旱事件的特征指标,分析了石羊河流域水文干旱演变特征,并采用与降水量、最高气温、最低气温、平均气温、蒸发量的相关性来分析石羊河流域SDI的影响因素。结果表明：1961—2017年石羊河流域干旱历时、干旱烈度和干旱强度的变化不是很一致,流域水文干旱历时20世纪70年代最长,80年代最短;干旱烈度全流域90年代最强,烈度最弱出现在80年代;干旱强度全流域60年代最强,80年代强度最弱;石羊河流域及流域中、西部年SDI变化总体上表现为在波动中呈增加趋势,西部增加幅度最大,中部增加幅度很小,流域东部年SDI在波动中呈减小趋势;石羊河全流域及流域东、中和西部年及四季干旱发生频次总体都是中旱和重旱频次最多,四季水文干旱发生频率最高的是春季,冬季干旱发生频率最低;从流域不同地段看,水文干旱发生的频率流域东部最高;构建的SDI 临界值识别出的主要水文干旱事件和实际干旱事件基本一致,干旱等级也较一致,说明使用SDI能够较好地监测到石羊河流域干旱年份及干旱等级;石羊河流域年SDI值与最高气温、平均气温和蒸发量呈负相关,与降水量和平均气温呈正相关。     

Impact of rainfall variability and grazing pressure on plant diversity in Mongolian grasslands

Climate and grazing are the main drivers of plant community composition and species richness in arid environments. This study aimed to examine the vegetation response to a spatial precipitation gradient, interannual rainfall variability, and grazing pressure in Mongolia. To examine the effect of a spatial precipitation gradient, we compared species richness among six sites. To investigate the effects of interannual rainfall variability and grazing pressure, we compared species richness for 2 years at two sites, in desert-steppe and steppe areas. The regional gradient in annual precipitation showed positive and negative relationships with grass richness and shrub richness, respectively, although total species richness did not vary significantly. The proportions of the different functional groups were affected by grazing pressure and rainfall variability in both zones. In the desert-steppe zone, species richness was lower in the drier year but did not vary with grazing pressure. In the steppe zone, species richness varied significantly with grazing pressure but did not vary between years. Precipitation would be more important than grazing pressure on vegetation changes in drier areas with high rainfall variability.