Low impact of climate change on subalpine grasslands in the Swiss Northern Alps

While phenological shifts and migration of isolated species under climate change have already been observed on alpine summits, very few studies have focused on community composition changes in subalpine grasslands. Here we use permanent plots monitored since 1954 and precisely located phytosociological censuses from 1970 to study compositional changes of subalpine grasslands in two distinct regions of the Swiss Northern Alps. In both areas, warming trends during the monitoring period were associated with changes in land management (abandonment of goat and sheep pasturing or grazing replaced by mowing). Old and recent inventories were compared with correspondence analyses (CA). Ecological indicator values, community‐affinities and biological traits of the species were used to infer the factors responsible for triggering the observed changes. In both regions, subalpine grasslands were stable with smaller changes than have previously been observed in alpine environments. Only a few species appeared or disappeared and changes were generally limited to increasing or decreasing frequency and cover of certain taxa. At one site, grazing abandonment favored fallow species. Some of these species were located at their upper altitudinal distribution limits and may have spread because of rising temperatures. In both areas, declining species were predominantly alpine and low‐growing species; their decline was probably due to increased competition (e.g., shadow) with more vigorous subalpine taxa no longer limited by grazing. We conclude that vegetation communities can respond rapidly to warming as long as colonization is facilitated by available space or structural change. In the subalpine grasslands studies, changes were mainly driven by land management. These communities have a dense vegetation cover and newly arriving herbaceous species preferring warmer conditions may take some time to establish themselves. However, climate disturbances, such as exceptional drought, may accelerate community changes by opening gaps for new species.     

Effects of pioneer shrubs on the recruitment of the fleshy‐fruited tree Olea europaea ssp. cuspidata in Afromontane savanna

Question: Is seedling recruitment of a fleshy‐fruited tree in degraded Afromontane savanna dependent on shelter from pioneer shrubs, and is shelter availability related to shrub traits? Location: Degraded montane savanna in northern Ethiopia (13°36′N, 39°21′E). Method: Nurse plants of Olea europaea ssp. cuspidata seedlings were recorded using T‐square plotless sampling and clustered according to shrub traits, using Ward's method after Principal Components Analysis. Facilitation was further examined through experimental planting and Kaplan‐Meier survival analysis. Results: Both in grazed and protected areas, Olea recruits were found exclusively under shrubs, primarily under Euclea racemosa although Acacia etbaica was more abundant. Olea recruitment is distributed randomly at landscape scale, but depends on shelter at patch scale. Shelter ability is related to shrub shape and species identity. Dense multi‐stemmed shrubs with a wide base and crown on a mulch‐rich mound are key recruitment foci. Euclea shrubs have these favoured traits and probably act as preferential perching sites for avian seed dispersers. Soil and organic matter accumulation under Euclea shrubs may also create favourable conditions for Olea germination and survival. Experimentally planted seedlings had a better chance for survival under Euclea. Conclusions: Olea regeneration is probably subject to both passive (disperser‐mediated) and active facilitation. Small changes of shrub traits can alter the suitability of a patch for Olea recruitment. Protection of shrubs can increase facilitation for seedlings, while pruning may reduce competition for saplings and thus enhance forest succession. Planting of raised Olea seedlings under Euclea shrubs in years with a good rainy season may further assist forest restoration.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

Phytosociology and conservation of Carex hordeistichos Vill. in the Lorraine region (France)

Carex hordeistichos is a peri-Mediterranean species, which is rare over all its distribution range. In Lorraine (France), where the field investigations were conducted, as in other Western European areas, it is present only in secondary habitats, constituted of heavily trampled wet pastures and vehicle tracks on clayed soils. All plant communities with Carex hordeistichos described from Western European areas can be linked to the Carici hordeistichi-Trifolietum fragiferi association, classified in the Agropyro-Rumicion wet pasture alliance. The conservation of this threatened ruderal plant requires the maintenance of a high disturbance level through grazing, trampling and soil packing.     

北方农牧过渡带农户农业生产系统模式的生态评价和改良研究

农牧过渡带 (或农牧交错带、半农半牧区 )是指我国传统种植业区和传统畜牧业区的镶嵌结合地带。近世纪以来 ,由于人口剧增 ,垦草种粮面积不断扩大 ,滥垦、过牧、滥樵 ,使草地植被大面积消失 ,沙漠化和荒漠化日趋严重。据报道 ,目前我国北方农牧过渡带荒漠化土地面积已达 1 6 7×10 5ｈａ ,占土地总面积的 5 2 73% ,年增长率约为1 39% [3] 。赤峰市是我国北方农牧过渡带较典型、分布面积较大的地区。该地区资源类型丰富 ,互补优势明显 ,特别是农牧结合的潜力巨大。但长期以来这里区域生态环境恶化加剧 ,导致严重的贫困化。解决这一问题的关…     

几种牧草幼苗对冷蒿茎叶水浸提液化感作用的生理响应

采用沙培法对草木樨、披碱草、冰草和羊草进行幼苗生长试验,研究了不同浓度冷蒿茎叶水浸提液处理对4种牧草幼苗生长、根系活力、叶绿素含量以及抗氧化保护酶活性的影响,并采用气相色谱-质谱(GC-MS)联用技术对冷蒿茎叶水浸提液的化学成分进行了分析。结果表明:冷蒿茎叶水浸提液对草木樨、披碱草、冰草和羊草4种牧草幼苗生长有明显的影响,这种影响效应与牧草的种类及冷蒿茎叶水浸提液浓度显著相关。其中,25mgDw·mL-1的冷蒿茎叶水浸提液均表现出对4种牧草幼苗生长指标有极显著的抑制作用(P0.01),4种牧草幼苗根系活力分别降低了46.7%、65.9%、59.3%和66.7%,草木樨、披碱草和羊草幼苗叶绿素含量分别下降了47.3%、56.6%和46.7%。当冷蒿茎叶水浸提液浓度为10mgDw·mL-1时,对4种牧草幼苗体内超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性有显著的促进作用;当浓度为25mgDw·mL-1时,对4种牧草幼苗体内SOD、POD和CAT活性有显著的抑制作用,同时使幼苗体内丙二醛(MDA)的含量显著增加。冷蒿茎叶水浸提液有30种化感类次生代谢化合物,主要成分是樟脑(27.6%)、龙脑(10.1%)、蓍草苦素(9.8%)、桉树脑(8.7%)、喇叭烯醇(4.1%)和对-1-薄荷烯-4-醇(4.1%),占总量的60%以上。     

浙闽沿海生态牧场技术示范区浮游细菌群落和功能的时空变化

【目的】本文通过不同季节的4个航次调查研究了2个浙闽沿海生态牧场技术示范区的浮游细菌群落的变化,揭示了示范区菌群结构的时空变化,探究其对于海洋生态系统的潜在影响。【方法】使用16SrRNA基因扩增子测序技术,对2个示范区4个季节航次共128个样点中浮游细菌的16SrRNA基因V4区序列进行测序,并通过分析其组成和多样性,借助FAPROTAX功能预测,分析不同季节和示范区浮游细菌的差异。【结果】128个样品量化后共获得2510976条优质序列,2个示范区的主要优势浮游细菌类群均为α变形菌纲、γ变形菌纲、β变形菌纲、放线菌纲、黄杆菌纲等,2个示范区浮游细菌的α多样性指数随季节演替而产生波动,且大多数环境因子都与其具有显著相关性;浙闽沿海浮游细菌的群落构建过程随时空变化而产生差异,扩散限制是2个示范区浮游细菌群落构建过程中占比最大的生态过程(除台山岛示范区秋季),2个示范区多数季节的浮游细菌群落相似性基于Bray-Curtis的地理距离衰减印证了这一点;基于FAPROTAX功能预测得到的2个示范区浮游细菌的功能以化能异养和氮硫循环为主,从一定程度上与当地的环境因子变化相关联。【结论】浙闽沿海...     

西藏高原退化土壤的生物学肥力及其变化特征

通过3年田间定位试验,对施肥条件下退化山地灌丛草原土生物学肥力的变化进行了研究.结果表明,不施肥状态下的耕层土壤有机质含量较试前呈微弱下降,施肥条件下土壤生物学肥力呈现出相对一致的特征,表现在耕层土壤有机质相对较高的积累速率、腐殖质结构明显改善以及土壤细菌的显著增殖等方面,但土壤微生物区系仍处于极不协调状态;随着有机肥或化肥的递增,0～30和30～60 cm土层有机质含量均有显著提高的趋势,其年均累积量分别达1.35和0.67 g·kg^-1;0～30和30～60 cm土层腐殖质碳占有机碳比重、胡敏酸碳占腐殖质碳比重亦均随有机肥或化肥递增而趋于提高;不同培肥方式对土壤细菌的繁殖与活动均具有极为显著的促进作用,2～30和30～60 cm土层细菌数量与有机质含量分别呈极显著和显著正相关（r＝0.7194、0.6042）,对土壤真菌、放线菌的影响则不甚明显;多数施肥处理下,不同土层固氮菌、纤维素分解菌数量低于不施肥处理,耕层土壤固氮菌与纤维素分解菌数量呈负相关（r=-0.4799）     

生态系统退化程度诊断：生态恢复的基础与前提

 生态系统退化程度诊断是进行生态恢复与重建的基础和前提。然而目前的生态系统化程度诊断大多停留在定性的水平,如何对退化生态系统的退化程度进行定量的诊断就成为恢复生态学与生态恢复实践所面临的一个迫切且十分关键的问题。在综述前人研究的基础上,比较系统地论述了生态系统退化程度诊断的一系列问题：绘制了描述生态系统退化程度的概念模型;认为在实践中退化程度诊断的参照系统可以选择相应的受人类或自然干扰程度比较轻的“自然生态系统”;归纳了生态系统退化程度诊断的生物途径、生境途径、生态过程途径、生态系统功能/服务途径、景观途径;把诊断方法分为单途径单因子诊断法、单途径多因子诊断法、多途径综合诊断法;分析了生态系统退化程度诊断的可能指标（体系）;给出了生态系统退化程度诊断的策略与流程,并对生态系统退化程度诊断及生态恢复过程中应注意的事项进行了讨论。建议我国加强典型生态系统退化程度的综合诊断研究。     

伊犁河谷春秋草场草地生态调查及其恢复对策

针对新疆伊犁河谷春秋草场严重退化的现状,通过对退化草场、围栏封育并实施灌溉的草场、单纯围栏的草场和灌溉但不封牧草场样方的对比调查,从地表植物的生物量、植物种类、优质牧草所占比例和草地植物多样性指数等的变化规律和特征方面,探讨了伊犁河谷地区春秋草场退化的原因和恢复措施。结果表明:适当灌溉后草地生物量为1540.5g.m-2,远高于不灌溉的草地(生物量为188.13g.m-2),表明干旱是本区草地植被生长一个重要制约因素;而仅改变草地的水分条件,在超载率达123%的大环境下,草场中优质牧草的比例由封育的62.38%下降到未封育的2.08%。因此,适度放牧并辅以灌溉措施是本区天然草场恢复的2个必要条件。