Growth response of Abies georgei to climate increases with elevation in the central Hengduan Mountains,southwestern China

Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues.     

华东天目山脉、黄山山脉、大别山脉竹类植物区系分析,兼论区系的起源与扩散

华东天目山脉、黄山山脉、大别山脉竹类植物较为丰富,分别有10属/75种(含种下等级)、8/49、7/30.通过对属、种的分布型分析,前二者竹类植物区系属于典型的华东区系,起源的时间不迟于早第三纪的始新世;而大别山脉虽仍属华东区系的范畴,因渗入了不少华中区系的成分,已具有某些经向过渡性特征,且起源的时间较晚.这3个山脉的竹类植物区系均具有显著的亚热带性质.天目山脉不仅是刚竹属Phyllostachys和短穗竹属Brachystachyum的分化变异中心,也极有可能就是它们的起源中心,但它们自此地起源后的散布方式有所不同,刚竹属在我国亚热带为四周放射状顺序渐进,扩散的范围颇广;短穗竹属存在东西南北4条散布路线,但向各方扩散的距离相差甚远.这些山脉与华东其他地区竹类植物区系联系密切,与华中竹类植物区系也有一定的联系,但与华南、西南等地竹类植物区系联系微弱.从地理位置和区系组成来看,黄山山脉的竹类植物区系来源于天目山脉,大别山脉的竹类植物区系又来源于黄山山脉,前者都是在后者扩展的基础上融合了其他区系的一些成分后发展而成,大别山脉又是北方秦岭以东广大丘陵平原地区竹类植物区系的发祥地.     

秦岭地区林地与草地景观格局变化及其驱动因素

以1980—2015年土地利用数据集为数据源,利用GIS空间分析、景观格局指数和主成分分析法,研究了秦岭地区林地与草地景观格局时空变化特征,并探讨其演化的驱动因素。结果表明:(1)林地和草地是秦岭地区主要景观类型,约占研究区总面积的72%,其中有林地为优势景观类型,其次为高覆盖度草地和中覆盖度草地,其他林地和低覆盖度草地分布面积相对较少。(2)35年来,林地和草地总面积整体呈减少趋势,净减少了309.44km²,其中草地减少占主导地位;空间变化上,损失严重的区域主要分布于以西安市为中心的周边区域,主要向建设用地和耕地转移。(3)林地和草地景观破碎化程度逐渐增加,连通性降低,景观异质性增强且景观形状更为复杂,草地较林地变化明显;空间分布上,林地和草地景观格局指数空间分布特征明显,在地形因子作用下呈现一定的地形梯度性,尤其与海拔的相关性最好。(4)人为活动干扰是影响秦岭地区林地和草地景观格局变化的主要驱动因素,气候因素次之,同时国家宏观政策起着重要的导向作用。减缓人为活动对秦岭地区的过度影响,维护林地和草地的平衡性及完整性,是实现该区生态系统科学管理和资源的可持续利用...     

秦岭南坡松栎林群落演替过程中物种组成及多样性动态分析

为揭示秦岭南坡植物群落演替与物种多样性之间的复杂关系,采用空间代替时间的方法在秦岭南坡油松林、松栎混交林和锐齿栎林群落典型分布区域设置45个样地进行了群落学调查,统计分析了油松林→松栎混交林→锐齿栎林这一演替序列过程中草、灌、乔3层的物种组成和α物种多样性动态。结果表明:(1)秦岭南坡油松林、松栎混交林和锐齿栎林3种群落共有维管植物312种,隶属于73科183属,其中草本植物136种,灌木(含木质藤本)98种,乔木78种;油松林群落包含52科117属190种,松栎混交林群落含有60科95属129种,锐齿栎林群落则为50科109属178种。(2)沿油松林→松栎混交林→锐齿栎林群落演替序列,草本层物种均匀度和物种多样性显著降低,物种丰富度呈"V"形变化趋势;灌木层物种丰富度、均匀度以及物种多样性均无显著差异;乔木层物种多样性呈明显的单峰型变化,其中松栎混交林群落物种多样性指数最高。研究表明,秦岭南坡松栎林群落物种多样性随演替进展总体上呈现单峰型变化,与中期物种多样性假说一致;物种多样性可能仅仅是群落稳定的一个基础或前提条件。     

Increased growth rates of stream salamanders following forest harvesting

Timber harvesting can influence headwater streams by altering stream productivity, with cascading effects on the food web and predators within, including stream salamanders. Although studies have examined shifts in salamander occupancy or abundance following timber harvest, few examine sublethal effects such as changes in growth and demography. To examine the effect of upland harvesting on growth of the stream‐associated Ouachita dusky salamander (Desmognathus brimleyorum), we used capture–mark–recapture over three years at three headwater streams embedded in intensely managed pine forests in west‐central Arkansas. The pine stands surrounding two of the streams were harvested, with retention of a 14‐ and 21‐m‐wide forested stream buffer on each side of the stream, whereas the third stream was an unharvested control. At the two treatment sites, measurements of newly metamorphosed salamanders were on average 4.0 and 5.7 mm larger post‐harvest compared with pre‐harvest. We next assessed the influence of timber harvest on growth of post‐metamorphic salamanders with a hierarchical von Bertalanffy growth model that included an effect of harvest on growth rate. Using measurements from 839 individual D. brimleyorum recaptured between 1 and 6 times (total captures, n = 1229), we found growth rates to be 40% higher post‐harvest. Our study is among the first to examine responses of individual stream salamanders to timber harvesting, and we discuss mechanisms that may be responsible for observed shifts in growth. Our results suggest timber harvest that includes retention of a riparian buffer (i.e., streamside management zone) may have short‐term positive effects on juvenile stream salamander growth, potentially offsetting negative sublethal effects associated with harvest.     

Ecosystem Responses to Nitrogen Deposition in the Colorado Front Range

We asked whether 3–5 kg N y⁻¹ atmospheric N deposition was sufficient to have influenced natural, otherwise undisturbed, terrestrial and aquatic ecosystems of the Colorado Front Range by comparing ecosystem processes and properties east and west of the Continental Divide. The eastern side receives elevated N deposition from urban, agricultural, and industrial sources, compared with 1–2 kg N y⁻¹ on the western side. Foliage of east side old-growth Englemann spruce forests have significantly lower C:N and lignin:N ratios and greater N:Mg and N:P ratios. Soil % N is higher, and C:N ratios lower in the east side stands, and potential net N mineralization rates are greater. Lake NO₃ concentrations are significantly higher in eastern lakes than western lakes. Two east side lakes studied paleolimnologically revealed rapid changes in diatom community composition and increased biovolumes and cell concentrations. The diatom flora is now representative of increased disturbance or eutrophication. Sediment nitrogen isotopic ratios have become progressively lighter over the past 50 years, coincident with the change in algal flora, possibly from an influx of isotopically light N volatilized from agricultural fields and feedlots. Seventy-five percent of the increased east side soil N pool can be accounted for by increased N deposition commensurate with human settlement. Nitrogen emissions from fixed, mobile, and agricultural sources have increased dramatically since approximately 1950 to the east of the Colorado Front Range, as they have in many parts of the world. Our findings indicate even slight increases in atmospheric deposition lead to measurable changes in ecosystem properties. Received 16 November 1999; accepted 8 February 2000.     

Climate sensitivity of conifer growth doesn’t reveal distinct low–high dipole along the elevation gradient in the Wolong National Natural Reserve,SW China

Recent climate warming is usually hypothesized to cause tree growth decline in the semi-arid regions where forests are particularly vulnerable to warming induced increases of water deficit. But there is still a large knowledge gap of climate warming effects on tree growth of cold temperate forest in the sub-humid region. Here we assess how climate warming has affected tree growth in the Wolong National Natural Reserve, Southwestern China, where recent warming might not cause tree growth decline because of the cold-humid climatic conditions. Tree-ring data from four co-dominant coniferous species (Larix potaninii var. macrocarpa, Tsuga chinensis, Abies faxoniana and Juniperus saltuaria) along an elevation gradient (from 2700 m to 3700 m) all imprinted temperature signals, and were both positively and significantly correlated with instrumental record of temperature data during the analyzed period of 1954–2010. Furthermore, the rising temperature since 1980 induced pervasive tree growth increases and stronger temperature signals for the coniferous species along the elevation gradient. The tree-ring chronology recorded a strong coherence with instrumental temperature since 1980 and was successful to keep up with the pace of climate warming rate. If climate warming continues, further increases in forest growth could be expected, and the terrestrial carbon sink will be strengthened for the local forest ecosystem in the future.     

黑颈鹤在新疆罗布泊和昆仑山分布及种群状况

黑颈鹤(Grus nigricollis)俗称"吐尔那",在新疆罕见,主要分布在与西藏和青海接壤的阿尔金山、昆仑山、喀喇昆仑山区.作者1985～2010年间在若羌(祁曼塔格、东昆仑山、阿尔金山)、且末(吐拉牧场、车尔臣河流域)、和田(阿克赛钦湖)、墨玉、皮山(喀拉喀什河流域)、叶城(叶尔羌河流域)等地记录到黑颈鹤.采用...     

Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m^–2 y^–1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.     

Genetic differentiation of Rubus chamaemorus populations in the Czech Republic and Norway after the last glacial period

The population structure of cloudberry (Rubus chamaemorus L.), collected from Krkonose Mountains (the Czech Republic), continental Norway and Spitsbergen, was examined using microsatellite analyses (SSR). Among 184 individuals, 162 different genotypes were identified. The overall unbiased gene diversity was high (). A high level of genetic differentiation among populations (F_ST = 0.45; p < .01) indicated restricted gene flow between populations. Using a Bayesian approach, six clusters were found which represented the genetic structure of the studied cloudberry populations. The value of correlation index between genetic and geographical distances (r = .44) indicates that gene flow, even over a long distance, could exist. An exact test of population differentiation showed that Rubus chamaemorus populations from regions (Krkonose Mountains, continental Norway and Spitsbergen) are differentiated although some individuals within populations share common alleles even among regions. These results were confirmed by AMOVA, where the highest level of diversity was found within populations (70.8%). There was no difference between 87 pairs of populations (18.7%) mostly within cloudberry populations from continental Norway and from Spitsbergen. Based on obtained results, it is possible to conclude that Czech and Norwegian cloudberry populations are undergoing differentiation, which preserves unique allele compositions most likely from original populations during the last glaciation period. This knowledge will be important for the creation and continuation of in situ and ex situ conservation of cloudberry populations within these areas.