1,721,011 research outputs found
Modelling of Vegetation Patterns and Functions in China Responding to Changes of Climates and Atmospheric CO2 Concentration
No full text利用BIOME4对全国植被格局的模拟显示，温度增加使得大部分森林分布区向北、向西迁移；稀树草原/干旱疏林、草原/干旱灌丛、干苔原扩张分布；苔 原植被类型的分布被逐渐限制到更高海拔的地区。降水增加后，湿润植被（如 各种森林和苔原）分布面积增加，而干旱植被（如稀树草原/干旱疏林、草原/干旱灌丛、干苔原）的分布面积则有所减少；温带和西藏地区的大部分植被类型 都向西扩张，并且逐渐深入到干旱的西北内陆地区。降水减少则表现出恰好相 反的效果。
大气CO2浓度倍增则在一定程度上补偿了干旱对湿润植被造成的不利影响。 大部分森林植被类型对设定的气候变化情景都表现出了较好的稳定性，特别是 在考虑了 CO2增浓的生理效应之后。而稀树草原/干旱疏林和苔原植被则表现出 高度的温度敏感性，即微小的增温幅度都会对这两种植被的分布区带来大面积 变化。对于湿润植被而言，构成威胁最大的气候情景是大气CO2浓度水平不变、 升温且伴随着降水的减少。森林和草原的过渡地带以及青藏高原将成为最为脆 弱的地区，在很多变化情景下，这里的植被类型都发生大面积的更替。
BIOME4碳储量模拟显示，CO2增浓可以使森林潜在碳储量显著增加40% 左右；升温对土壤呼吸的加强，会引起土壤碳库的减少。
其次，基于光能利用率和水分利用率的概念，我们对大量的中国森林净初 级生产力数据进行分析，首创了两个半经验的植被生产力模型，并通过和其他 大量的独立数据（草原地上部分净初级生产力，全球总初级生产力数据）和已 发表的研究成果（森林植被水分利用效率）进行比较，充分的肯定了该模型的 模拟能力及其结果的合理性。对该模型的模拟结果也进行了相应的敏感性分析， 以反映中国植被功能响应未来变化的趋势。为敏感性分析所设定的梯度为：一 个3.5。C的升温梯度，两个10%的降水增减梯度，大气CO2浓度还是保持近期 水平和倍增水平两个固定数值（366ppm和732ppm)。基于这些研究，我们提出 了植被功能响应大气CO2浓度升高的的上限和下限，并且探究了 DGVMs模拟 结果差异的原因。
结果表明，水分利用模型（WUEM)和光能利用模型（LUEM)都表现出 和所搜集到的其他数据库结果的普遍一致性，并且这两个模型对现实数据的描 述吻合度较高，相关系数分别达0.64和0.60。通过敏感性分析很容易看出，尽 管降水增减对植被功能的影响在两个模型中都显示出一致的变化规律，但在预 测植被功能响应大气CO2浓度和温度变化时，两套结果却表现出显著的差异。在植被生产力响应大气CO2增浓的研究中，水分利用模型给出的响应更为强烈， 可能的原因是该结果高估了茂密植被类型的响应能力，因为在该模型的假设中 没有考虑茂密植被区域径流可能增加的因素；同时相应的，光能利用模型的结 果又可能低估了稀疏植被对大气CO2浓度的响应能力，因为该模型假设没有考 虑到植被盖度可能增加的因素。而在升温响应的研究中，光能利用模型显示， 升温对华南地区的植被生产力造成明显的不利影响，因为升温并不能为该地区 植被带来生长季的延长；而水分利用模型的结果却表现出相反的结果，这主要 是因为华南地区充足的水分供应，在一定程度上避免了气孔关闭对CO2吸收的 限制作用。
两个模型所显示出的数量的差异，揭示了 DGVMs模拟全球植被生产力在响 应未来气候和大气CO2浓度变化时，响应程度甚至响应方向上巨大差异的可能 原因。由于目前并没有现实证据表明哪种响应更接近真实情况，我们模型研究 所揭示出的问题还需要野外实验的进一步分析论证
Data from: Morphological and moisture availability controls of the leaf area-to-sapwood area ratio: analysis of measurements on Australian trees
No full text<b>External Organisations</b><br/>Macquarie University; University of Melbourne; University of Technology Sydney<b>Associated Persons</b><br/>Kim Brooksbank (Creator)Henrique Furstenau Togashi (Creator); Ian Colin Prentice (Creator); Bradley John Evans (Contributor); David Ian Forrester (Creator); Paul Feikema (Creator); Derek Eamus (Creator); Daniel Taylor (Creator); Iain Colin Prentice (Creator)1. The leaf area-to-sapwood area ratio (LA:SA) is a key plant trait that links photosynthesis to transpiration. The pipe model theory states that the sapwood cross-sectional area of a stem or branch at any point should scale isometrically with the area of leaves distal to that point. Optimization theory further suggests that LA:SA should decrease toward drier climates. Although acclimation of LA:SA to climate has been reported within species, much less is known about the scaling of this trait with climate among species. 2. We compiled LA:SA measurements from 184 species of Australian evergreen angiosperm trees. The pipe model was broadly confirmed, based on measurements on branches and trunks of trees from one to 27 years old. Despite considerable scatter in LA:SA among species, quantile regression showed strong (0.2 < R1 < 0.65) positive relationships between two climatic moisture indices and the lowermost (5%) and uppermost (5–15%) quantiles of log LA:SA, suggesting that moisture availability constrains the envelope of minimum and maximum values of LA:SA typical for any given climate. 3. Interspecific differences in plant hydraulic conductivity are probably responsible for the large scatter of values in the mid-quantile range and may be an important determinant of tree morphology.,Supplementary information 1_LA_SA Togashi datasetHuber Value dataset for 183 evergreen angiosperm trees in Australia
The Burning Issue
No full textAntarctic ice cores reveal a 650-year record of biomass burning in the Southern Hemisphere.</jats:p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Terrestrial ecosystem modelling studies on the energy, water and carbonbalance of a seasonal semi-deciduous dry neotropical forest in Brazil.
Full text linkWe aim to develop a transferable terrestrial ecosystem model that could be applied as a scientific and management tool for Caatinga and other dry forests
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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