Can Establishment Characteristics Explain the Poor Colonization Success of Late Successional Grassland Species on Ex‐Arable Land?

Abstract Many grassland restoration projects on former arable land face problems because early successional grassland species establish vigorously and persistently but late successional grassland species fail to establish. Differences in establishment characteristics of early and late successional species might provide an explanation for the failure of many late successional species to colonize grasslands on ex‐arable land. I examined whether early and late successional species had different establishment rates in the initial years of a grassland succession, whether a specific establishment stage (seedling emergence, mortality or growth) could be identified as the key process controlling establishment, and what management would enhance the establishment of late successional grassland species. Seeds of three early and three late successional species were sown separately in ex‐arable plots with bare soil, 1‐year‐old vegetation, and 2‐year‐old vegetation. Emergence, mortality, and seedling growth were monitored for 1 year. Early successional species established successfully in the bare soil plots but failed to establish in plots with 1‐ and 2‐year‐old vegetation. Late successional species showed either lower establishment rates in the younger succession stages or decreased establishment with succession that nevertheless resulted in significant establishment in the oldest plots. Seedling emergence proved to be the key factor determining the establishment pattern of early and late successional species. In absolute numbers, emergence of late successional species was, however, similar or higher than that of early successional species, even in the earliest succession stage. The poor establishment of late successional species on former arable land could therefore not be explained solely by differences in establishment characteristics between early and late successional grassland species. Competitive processes between early and late successional species later in the life cycle probably play an important role. The results do point out that establishment of late successional species can be promoted by creating vegetative cover from the start of the restoration effort.     

Sensitivity of Soil Restoration Indicators during Páramo Succession in the High Tropical Andes: Chronosequence and Permanent Plot Approaches

The aim of this study was to analyze indicators of soil restoration during secondary succession in a heterogeneous valley in the high tropical Andes. A combination of chronosequence and permanent plot methods was used to detect changes in this heterogeneous matrix. Thirty-six plots with different fallow times (1–9 years) and four noncultivated plots with natural vegetation (páramo) were sampled twice in a 3-year interval (1996 and 1999). The following soil properties were determined: total C and N, pH, exchangeable bases, cation exchange capacity, and microbial biomass N (MB-N). Using the chronosequence approach, successional increases in soil pH and Mg were detected, pointing to these variables as indicators of soil restoration during the fallow period. Comparing the noncultivated páramo with the fallow plots, a significant decrease in MB-N was found, suggesting that this is a sensitive agricultural disturbance indicator. The permanent plot analysis failed to detect successional trends in any of the study variables, probably as a result of a lack of sensitivity of the indicators used within the 3-year interval. Nevertheless, a strong acidification was detected by the permanent plot method when fallow plots were cultivated. We conclude that the size of important soil components such as total soil organic matter or microbial biomass is not a sensitive soil restoration indicator in these heterogeneous mountain systems but that other integrative variables such as pH could be more sensitive to successional changes in key soil processes (e.g., nitrification or nutrient losses).     

Nitrogen‐dependent recovery of subarctic tundra vegetation after simulation of extreme winter warming damage to Empetrum hermaphroditum

Vast areas of (sub)arctic tundra are dominated by the ericoid dwarf shrub Empetrum hermaphroditum. Recent experimental and observational data have shown that Empetrum can be damaged heavily by recurrent extreme winter warming. In addition, summer warming leads to increased soil N availability in tundra ecosystems. In a 7‐year experiment, I investigated the recovery of subarctic Empetrum‐dominated tundra vegetation using a factorial combination of various degrees of aboveground Empetrum removal (simulating the damaging effects of extreme winter warming) and N addition (simulating one of the effects of summer warming). After 7 years no new species had established in the plots. The growth of planted Betula nana seedlings was stimulated by Empetrum removal and reduced by N addition. This Empetrum‐dominated tundra ecosystem was resilient against severe disturbances. Only when Empetrum was 100% removed did it fail to recover, and only in combination with high N supply the subordinate species (notably Eriophorum vaginatum and Rubus chamaemorus, a graminoid and a forb) could benefit. In the 50% removal treatment Empetrum recovered in 7 years when no N was supplied and the cover of the subordinate species did not change. However, when N was added Empetrum recovered faster (in 4 years) and the subordinates decreased. When Empetrum was not removed and N was added, Empetrum even increased in abundance at the expense of the subordinate species. Thus, profound changes in tundra ecosystems can only be expected when Empetrum is very heavily damaged as a result of recurrent extreme winter warming and when soil N availability is increased as a result of summer warming. These changes in species composition upon extreme disturbance events may lead to a wide variety of ecosystem feedbacks and cascade processes as this tundra system is relatively species‐poor, and can be hypothesized to have low functional redundancy.     

Seasonal and interannual variations in carbon dioxide exchange over a cropland in the North China Plain

In China, croplands account for a relatively large form of vegetation cover. Quantifying carbon dioxide exchange and understanding the environmental controls on carbon fluxes over croplands are critical in understanding regional carbon budgets and ecosystem behaviors. In this study, the net ecosystem exchange (NEE) at a winter wheat/summer maize rotation cropping site, representative of the main cropping system in the North China Plain, was continuously measured using the eddy covariance technique from 2005 to 2009. In order to interpret the abiotic factors regulating NEE, NEE was partitioned into gross primary production (GPP) and ecosystem respiration (R_eco). Daytime R_eco was extrapolated from the relationship between nighttime NEE and soil temperature under high turbulent conditions. GPP was then estimated by subtracting daytime NEE from the daytime estimates of R_eco. Results show that the seasonal patterns of the temperature responses of R_eco and light‐response parameters are closely related to the crop phenology. Daily R_eco was highly dependent on both daily GPP and air temperature. Interannual variability showed that GPP and R_eco were mainly controlled by temperature. Water availability also exerted a limit on R_eco. The annual NEE was ?585 and ?533 g C m^?2 for two seasons of 2006–2007 and 2007–2008, respectively, and the wheat field absorbed more carbon than the maize field. Thus, we concluded that this cropland was a strong carbon sink. However, when the grain harvest was taken into account, the wheat field was diminished into a weak carbon sink, whereas the maize field was converted into a weak carbon source. The observations showed that severe drought occurring during winter did not reduce wheat yield (or integrated NEE) when sufficient irrigation was carried out during spring.     

葱蝇非滞育、 冬滞育和夏滞育蛹发育和形态特征比较

昆虫非滞育、 冬滞育和夏滞育蛹具有不同的生理和发育过程。本研究以葱蝇Delia antiqua作为模式种, 以黑腹果蝇Drosophila melanogaster蛹的发育形态特征和命名为参照, 用解剖、 拍照、 长度测量和图像处理等方法系统地比较研究了非滞育、 冬滞育和夏滞育蛹的发育历期和形态变化, 重点在头外翻和滞育相关发育和形态特征, 目的在于弄清非滞育、 冬滞育和夏滞育蛹发育和形态特征差异, 为滞育发育阶段的识别、 滞育分子机理研究奠定形态学基础。冬滞育蛹的滞育前期、 滞育期和滞育后期分别为4, 85和27 d, 夏滞育蛹的滞育前期、 滞育期和滞育后期分别为2, 8和22 d。从化蛹至头外翻完成为滞育前期, 头外翻完成约10 h内复眼中央游离脂肪体可见。头外翻的完成是滞育发生的前提, 非滞育、 夏滞育和冬滞育蛹头外翻发生在化蛹后的48, 36和83 h, 在头外翻过程中发育形态没有差异。头外翻的过程为： 首先, 头囊和胸部附肢从胸腔外翻, 头部形态出现; 然后, 腹部肌肉继续收缩, 将血淋巴和脂肪体推进头部及胸部附肢。葱蝇蛹在完成蛹期有效积温约15%时进入冬滞育或夏滞育。在滞育期, 蛹的形态一直停留在复眼中央游离脂肪体可见这一形态时期, 且冬滞育和夏滞育的蛹在形态上没有区别。在体长、 体宽和体重上, 冬滞育蛹最大, 夏滞育蛹次之, 非滞育蛹最小。在滞育后期, 在黄色体出现期间, 非滞育蛹的马氏管清楚可见, 呈绿色, 而滞育蛹的马氏管几乎不可见。本研究为认知昆虫滞育生理、 从发育历期和形态上推断滞育发育进程提供了依据。     

大兴安岭林区驯鹿夏季喜栖生境的生态特征

2012和2013年7—8月采用样线和样带调查结合的生境调查方法,对分布于我国大兴安岭西北麓的驯鹿的夏季偏好生境开展了对比研究,并对样地的海拔和乔木郁闭度等23个生境变量进行测量及比较.结果表明: 与对照样地相比,夏季驯鹿利用样地的海拔(926.9±0.8 m)、乔木郁闭度(17.9%±2.4%)、乔木胸径(35.5±2.1 cm)、乔木高度(8.2±0.5 m)、乔木密度(6.9±0.5 株·400 m^-2)及树桩数(1.3±0.2 个·400 m^-2)较大,但灌木均高(54.2±2.0 cm)较小(P<0.01).驯鹿夏季偏好选择坡度较缓的中坡生境,因其夏季喜栖生境的水源较多、隐蔽度和避风性较差,距人为干扰距离和牧民点距离均较远.主成分分析(PCA)表明,干扰强度(由距人为干扰距离及距牧民点距离变量组成)、乔木特征(由乔木的高度、密度、胸径和郁闭度变量组成)、地理特征(由坡位、坡向和土壤湿润度变量组成)、食物多度(地表植被盖度和灌木盖度变量构成)、开阔度(由隐蔽度和避风状况变量构成)和坡度是影驯鹿夏季生境选择的重要因素.这6个因子提供了70.7%的累积贡献率,主要反映了驯鹿夏季在喜栖生境选择中的食物资源、抗干扰性和反捕需求.从夏季喜栖生境的生态特征来看,驯鹿并没有被完全驯化.在保护和管理实践中,应使驯鹿种群及其核心栖息地免受高强度的人为干扰.     

Modelling geographical variation in voltinism of Hylobius abietis under climate change and implications for management

相似文献   

Carbon storage and root penetration in deep soils under small-farmer land-use systems in the Eastern Amazon region,Brazil

The north-east of Pará state in the Eastern Amazon of Brazil was settled over 100 years ago. Today the region is an agricultural landscape with variously-aged secondary vegetation and fields with annual cultures, plantation crops and pastures. The effect of these different land covers on carbon sequestration as well as on water and nutrient extraction remain subject of debate. Therefore, we assessed the importance of land use on soil carbon stocks by measuring various C fractions and root biomass (0–6 m) in slash-and-burn systems and (semi-) permanent cultures. An extensive root system down to at least 6 m depth was present under various secondary vegetation stands and slashed and burned fields recently taken into cultivation as well as under a primary forest. Shallower rooting patterns were evident under (permanent) oil palm (4.5 m) and (semi-permanent) passion fruit plantations (2.5 m). Carbon storage in soils of traditional slash-and-burn agriculture up to 6 m depth (185 t ha^-1) was not significantly lower than under a primary forest (196 t ha^-1) but declined significantly under (semi-) permanent cultures (to 146–167 t ha^-1). Compared to above-ground C losses, soil C losses due to slash-and-burn agriculture may thus be small. This is an argument for maintaining the secondary vegetation as part of the agricultural land-use system, as the root system of its trees is conserved and thus C is sequestered also at greater depth.     

高温条件下棉铃虫化蛹率、夏滞育率和蛹重的变化

在预蛹期,高温处理能诱导棉铃虫蛹进入夏滞育。本实验着重就33～39℃的变温下滞育蛹和未滞育蛹的失重动态进行了对比研究,同时以常温（27℃）下蛹作为参照。研究发现： 在33～39℃的变温条件下,棉铃虫化蛹率显著低于其在常温下的化蛹率,且所化蛹中有63.2%的雄性和10.9%的雌性进入高温夏滞育,其中高温滞育蛹和未滞育蛹分别都轻于正常发育蛹。化蛹后第2日至第5日期间,高温滞育蛹失重量显著低于高温未滞育蛹和正常发育蛹的失重量,分别为3.62、13.30和5.49 mg;蛹期总失重量结果与化蛹后第2～5日间蛹失重量趋势一致,高温滞育蛹、未滞育蛹和正常发育蛹失重量分别为15.60、49.35和26.30 mg。蛹失重动态研究发现高温滞育蛹在夏滞育期间其失重曲线平缓,显著低于高温未滞育蛹和正常发育蛹;高温滞育蛹滞育解除后,其失重曲线与正常发育蛹的失重趋势基本一致。结果表明,棉铃虫夏滞育蛹能通过维持低的代谢水平来度过不利环境,具有一定的生态适应意义。     

新疆伊犁河湿地及周边夏季鸟类调查初报

2006年6～8月,调查了新疆伊犁河湿地及其周边夏季鸟类,共记录到16目36科96种,种群数量为3110只,水鸟占优势,共57种.其中复候鸟52种、留鸟33种、旅鸟11种;在85种繁殖鸟中,古北界52种、东洋界8种、广布种25种,分别占总种数的61.18%、9.41%、29.41%.有国家I、Ⅱ级保护鸟类13种,新疆特有种或亚种17种.鸟类生态分布显示,下游三道河一伊犁河大桥地段拥有较丰富的鸟类种群.通过调查,提出了一些鸟类保护对策.