Using consecutive prescribed fires to reduce shrub encroachment in grassland by increasing shrub mortality

Woody plant encroachment into open grasslands occurs worldwide and causes multiple ecological and management impacts. Prescribed fire could be used to conserve grassland habitat but often has limited efficacy because many woody plants resprout after fire and rapidly reestablish abundance. If fire‐induced mortality could be increased, prescribed fire would be a more effective management tool. In California's central coast, shrub encroachment, especially of Baccharis pilularis (coyote brush), is converting coastal prairie into shrub‐dominated communities, with a consequent loss of native herbaceous species and open grassland habitat. B. pilularis has not been successfully controlled with single prescribed fire events because the shrub resprouts and reestablishes cover within a few years. We investigated whether two consecutive annual burns would control B. pilularis by killing resprouting shrubs, without reducing native herbaceous species or encouraging invasive plants. As expected, resprouting did occur; however, 2 years after the second burn, B. pilularis cover on burned plots was only 41% of the cover on unburned plots. Mortality of B. pilularis more than doubled following the second burn, likely maintaining a reduction in B. pilularis cover for longer than a single burn would have. Three native coastal prairie perennial grasses did not appear to be adversely affected by the two burns, nor did the burns result in increased cover of invasive species. Managers wanting to restore coastal prairie following B. pilularis encroachment should consider two consecutive annual burns, especially if moderate fire intensity is achievable.     

Success of active restoration in grasslands: a case study of birds in southern Brazil

Grasslands in southeastern South America have been extensively converted to various land uses such as agriculture, threatening regional biodiversity. Active restoration has been viewed as a management alternative for recovery of degraded areas worldwide, although most studies are conducted in forests and none has evaluated the effect of active restoration of grasslands in southeastern South America. From 2015 through 2017 we monitored a federally owned tract of grassland from the beginning of the active‐restoration process. We compared the bird community in this active‐restoration area (AR) with a reference area (NG) in Pampa grasslands in southern Brazil. We sampled birds by point counts and surveyed vegetation structure in plots. Over the 3 years of active restoration, bird species richness and abundance were higher in AR (30 species, 171 individuals) than NG (22 species, 154 individuals). The species composition also differed between the two habitats. Grassland bird species were present in both AR and NG. The vegetation structure differed between AR and NG in five attributes: height, short and tall grasses, herbs, and shrubs. Since it has been found that active restoration is useful in promoting species diversity, we encourage studies of the use of long‐term restoration efforts. Our study, even on a local scale, showed a rapid recovery of the bird community in the active‐restoration compared to native grassland, and suggests the potential for recovery of the degraded grasslands of the Brazilian Pampa biome.     

Leaving uncut refuges during meadow harvesting increases the functional diversity of Orthoptera

In the past, insect species richness was high in Central European seminatural grasslands, which were characterized by low‐intensity land use. Currently, however, the hay in most of these grasslands is mechanically harvested, which negatively impacts insect biodiversity. One way to reduce this negative effect is to leave unmown patches as refuges. In the current research we evaluated the short‐term effects of leaving an unmown patch on the taxonomic and functional diversity of the Orthoptera assemblage in a meadow. We found that orthopteran species richness and abundance were significantly reduced by mowing, whether or not a patch was left uncut. In contrast, functional evenness, indicating distribution of species abundances in a niche space, was reduced by mowing only if the plot lacked an uncut refuge. Functional richness, indicating the amount of niche space occupied by species, was elevated if the plot had an uncut refuge. Larger species were negatively affected by mowing, while habitat specialists, mobile species and soil‐ovipositing species benefitted from it. We infer that the presence of an uncut patch increased the diversity of habitats available to orthopterans and maintained even distribution of species among niche space. In summary, leaving an unmown refuge in grasslands could increase the functional diversity of orthopterans, even if it does not preserve taxonomic diversity.     

Fresh,frozen or fake: A comparison of predation rates measured by various types of sentinel prey

Arthropod predators and parasitoids support the health and functioning of the world's ecosystems, most notably by supplying biological control services to agricultural landscapes. Quantifying the impact that these organisms have on their prey can be challenging, as direct observation and measurement of arthropod predation is difficult. The use of sentinel prey is one method to measure predator impact; however, despite widespread use, few studies have compared predation on different prey types within a single experiment. This study evaluated the predation rates on four sentinel prey items in grass and wheat fields in south-east Queensland, Australia. Attack rates on live and dead Helicoverpa armigera eggs, and dead H. armigera larvae and artificial plasticine larvae, were compared and the predators that were attracted to each prey type were documented with the use of field cameras. There was no significant difference in predation rates between sentinel eggs, while dead larvae were significantly more attacked than artificial larvae. Prey were attacked by a diverse range of predators, including ants, beetles, various nymph and juvenile insects and small mammals. Different predators were active in grass and crop fields, with predator activity peaking around dawn and dusk. The same trends were observed within and between the two habitats studied, providing a measure of confidence in the sentinel prey method. A range of different sentinel prey types could be suitable for use in most comparative studies; however, each prey type has its own benefits and limitations, and these should be carefully evaluated to determine which is most suitable to address the research questions.     

北方农牧交错带温性盐碱化草地土壤呼吸对不同形态氮添加和刈割的响应

农牧交错带草地生态系统兼受农业和牧业的影响, 属于脆弱生态系统, 尤其是养分贫瘠的盐碱化草地, 其生态系统结构和功能对外界干扰的响应更加强烈。位于晋西北地区的农牧交错带盐碱化草地, 地理位置独特, 区别于天然牧区草地生态系统。由于毗邻农田, 农业氮肥的过量使用促进了活性氮气体排放, 同时使得农牧交错带草地土壤碳氮循环发生改变。刈割是北方农牧交错草地生态系统的主要管理方式, 为了深入探究氮添加和刈割管理方式对农牧交错带草地碳循环的影响, 进一步厘清该区域草地生态系统的碳动态问题, 该研究设置了一个不同形态氮添加和刈割的裂区实验, 测定土壤呼吸对不同形态氮肥添加和刈割的响应, 为进一步科学管理该区域草地提供可靠的依据。实验样地位于山西省右玉县境内的“山西农业大学农牧交错带草地生态系统野外观测研究站”, 于2017年设置不同形态氮添加和刈割处理, 实验处理包括对照(不刈割和刈割)、尿素添加、缓释尿素添加、刈割+尿素添加、刈割+缓释尿素添加, 每种处理6个重复, 共36个小区。在不同处理条件下测定土壤呼吸速率、土壤温度、土壤水分、土壤微生物生物量、土壤无机氮含量、植物地上和地下生物量, 并计算土壤累积碳排放量及CO₂通量。研究结果表明: (1)短期(2017-2018年)尿素和缓释尿素的添加显著提高了该地区土壤呼吸速率和土壤累积碳排放量。与添加缓释尿素相比, 添加尿素处理下的土壤呼吸速率和累积碳排放量更高; (2)刈割显著降低土壤呼吸速率和累积碳排放量; (3)短期氮添加和刈割的交互作用对土壤呼吸速率没有显著影响。因此, 短期氮添加促进了北方农牧交错带盐碱化草地土壤碳释放, 刈割抑制土壤呼吸, 降低了累积碳排放量, 这可能是由于刈割移除地上植物, 减少了凋落物的输入, 底物减少导致土壤微生物活性降低。但是随着处理时间的延长, 氮添加和刈割对该农牧交错带盐碱化草地土壤碳动态的影响还有待进一步探究和发现。     

极端干旱对草甸草原优势植物非结构性碳水化合物的影响

植物光合作用产生的非结构性碳水化合物(NSCs)水平可以反映植物和生态系统对环境变化的响应程度。近年来, 草原极端干旱事件的发生频率和持续时间增加趋势明显, 对生态系统结构和功能产生深远影响。该研究以内蒙古呼伦贝尔草甸草原为研究对象, 通过连续4年减少66%生长季降水量的控制实验来模拟极端干旱事件, 分析草原6种优势物种和植物功能群NSCs各组分对极端干旱的响应规律与机制。结果显示, 由于植物生物学、光合特性以及生理生态等特性的差异, 不同物种对干旱胁迫的响应具有明显差异。这表明草地植物NSCs组分及其利用策略对干旱胁迫的响应具有物种特异性, 从而导致其生物量的不同响应。将6种植物分为禾草和非禾草两类, 发现干旱显著增加了禾草的淀粉含量, 但对其可溶性糖含量无显著影响; 相反, 干旱显著增加了非禾草功能群的可溶性糖含量, 对其淀粉含量无显著影响, 表明不同功能群采取了不同的干旱应对策略。禾草选择将光合作用固定的能量进行储存以应对干旱胁迫, 其生物量对干旱响应不敏感; 而非禾草选择将能量以可溶性糖的形式直接供植物生长利用以及抵御干旱胁迫, 其生物量对干旱响应较为敏感。这一发现可为预测在全球气候变化背景下草甸草原生态系统结构与功能对极端干旱的响应提供科学参考。     

全球变化背景下内蒙古草原土壤微生物多样性维持机制研究进展

全球变化对人类环境的影响是近几十年世界广泛关注的热点之一。内蒙古草原不仅是我国重要的牲畜和饲料生产基地, 而且有着不可替代的生态系统功能。土壤微生物是地球上多样性最高的生物类群, 在驱动碳氮循环等多种生态系统过程中发挥着至关重要的作用。由于研究技术的限制和群落结构复杂等原因, 土壤微生物生态学研究还处于描述性阶段, 理论研究还很缺乏。鉴于此, 利用分子生物学技术尤其是新一代测序技术, 从理论层面上系统地研究全球变化背景下我国北方草地微生物多样性的维持机制具有重要意义。本文在比较各种环境变化对土壤微生物群落的相对影响的基础上, 分析全球变化对微生物多样性影响的物理化学和生态学机制, 并对未来内蒙古草原微生物多样性的重点研究领域进行了展望, 包括: (1)加强全球变化多因素综合研究; (2)加强微生物多样性维持的生态学机制的研究; (3)加强地上与地下多样性关联机制的研究; (4)加强全球大尺度多生态系统的整合研究。     

围封对天山高寒草原4种植物叶片和土壤化学计量学特征的影响

以中国科学院巴音布鲁克草原生态系统研究站长期围栏内外的羊茅(Festuca ovina)、天山赖草(Leymus tiansecalinus)、二裂委陵菜(Potentilla bifurca)和鹅绒委陵菜(Potentilla anserine)4种植物叶片和土壤为研究对象,分析了放牧与围封对植物叶片和土壤C、N、P的化学计量特征的影响。结果表明,围封样地土壤养分浓度整体高于放牧样地(P0.05),全氮(TN)浓度除外。围封显著增加羊茅叶片C、N浓度(P0.05),对P浓度影响不显著;围封显著增加鹅绒委陵菜叶片的C浓度,但是显著降低叶片的N和P浓度(P0.05),围封对天山赖草和二裂委陵菜养分含量影响不显著。围封显著增加鹅绒委陵菜C∶N和C∶P(P0.05);围封显著降低羊茅C∶N、C∶P和增加N∶P(P0.05);围封显著降低二裂委陵菜C∶N(P0.05),对天山赖草的化学计量特征影响不显著。不同植物对围封的响应不同,意味着长期围封可能会改变天山高寒草原生态系统的结构。围封降低优势种(羊茅)的固碳能力,增加退化期出现的代表性植物(鹅绒委陵菜)的固碳能力,表明在长期围封下植物凋落物中的杂类草(鹅绒委陵菜)可能更多的为土壤提供碳来源,也能促进优势禾本科物种的氮含量和碳含量的增加。     

乌鲁木齐山地草地生态系统服务价值变化评估——基于遥感与GIS

草地生态系统服务功能是指草地生态系统及其生态过程所形成和维持的人类赖以生存的自然环境及其有效性,中国干旱半干旱地区的草地退化严重制约着生态系统服务功能的。以乌鲁木齐市山地草地为研究靶区,利用遥感图像(Landsat TM/OLI)划分出7种不同草地类型并计算其生态系统服务价值(Ecosystem Service Values, ESV)。使用空间统计方法、网格分析、空间自相关等方法进一步分析研究区山地草地退化程度和ESV变化。结果表明:21年中,乌鲁木齐市草地生态系统服务价值呈现波动性下降趋势,年均减少0.27×10~7元。生态损失主要是由山地荒漠草地(7.44%)、山地荒漠草原草地(10.71%)、山地草甸草原草地(18.32%)和高寒草甸草地(40.69%)退化造成。单项生态系统服务价值中,草地对调节服务(土壤形成)和供给服务的贡献率较高。草地ESVs Moran平均值为0.869(1994—2015年),并且草地ESV与相邻网格(2 km×2 km)具有更高的空间相关性。草地ESV具有明显的空间分布特征,高ESV区基本上分布在南山山区,低ESV区主要分布在平原草地区,博格达山草地亚区呈现随机分布格局。研究区气候变化对草地的影响十分显著,平均气温、平均地表温度、湿度、蒸散量、降水量和风速对草地ESV变化均有一定的影响,过度放牧、不合理垦荒、药用植物过度开发、城市化等人为活动仍然是驱动草地退化的主要因子,因此亟需采取措施保育乌鲁木齐市山地草原生态系统。     

气候变化与人类活动对内蒙古东部草地净初级生产力的影响

内蒙古东部草地是该区域的主体生态系统类型,属于脆弱的生态系统,对气候和人类活动反应敏感。基于土地覆被数据和改进CACS模型,估算得到的草地NPP,分析2000-2015年内蒙古东部草地和NPP时空格局与年际动态。进而,定义相对退化指数（RDI）,确定草地生产力变化过程中人类活动因素的贡献率,分析内蒙古东部地区2000-2015年RDI空间格局与年际动态。同时,分析16年间NPP和气候因子相关关系。结果表明：1）2000-2015年间,损失草地面积4743.80 km²,新增草地面积2705.57 km²。2）2000-2015年内蒙古东部地区草地植被平均NPP位于166.56-248.14 gC m^-2 a^-1之间,NPP在波动中呈现明显的上升趋势（3.65 gC m^-2 a^-1/a,R²=0.47）。3）2000-2015年RDI在16.64%-30.54%之间波动,RDI值呈缓慢下降趋势,表明人类活动对草地植被净初级生产力的干扰程度在下降。4）草地NPP变化主要是因为草地本身生产力下降。整体来看相关草地保护工作取得了阶段性进展,草地生境质量得到有效缓解,草地生态环境得到转变。