共查询到20条相似文献，搜索用时 15 毫秒
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Cowling Sharon A. 《Global Ecology and Biogeography》1999,8(2):81-93
1. Physiological experiments have indicated that the lower CO2 levels of the last glaciation (200 μmol mol?1) probably reduced plant water-use efficiency (WUE) and that they combined with increased aridity and colder temperatures to alter vegetation structure and composition at the Last Glacial Maximum (LGM). 2. The effects of low CO2 on vegetation structure were investigated using BIOME3 simulations of leaf area index (LAI), and a two-by-two factorial experimental design (modern/LGM CO2, modern/LGM climate).3. Using BIOME3, and a combination of lowered CO2 and simulated LGM climate (from the NCAR-CCM1 model), results in the introduction of additional xeric vegetation types between open woodland and closed-canopy forest along a latitudinal gradient in eastern North America.4. The simulated LAI of LGM vegetation was 25–60% lower in many regions of central and eastern United States relative to modern climate, indicating that glacial vegetation was much more open than today.5. Comparison of factorial simulations show that low atmospheric CO2 has the potential to alter vegetation structure (LAI) to a greater extent than LGM climate.6. If the magnitude of LAI reductions simulated for glacial North America were global, then low atmospheric CO2 may have promoted atmospheric warming and increased aridity, through alteration of rates of water and heat exchange with the atmosphere. 相似文献
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Aim The goal of this study was to determine the extent of suitable habitats across the basins and ranges of the Great Basin for 13 montane mammals in the present and during the Last Glacial Maximum (LGM). For all these mammal species, we test whether: (1) more suitable habitat was available in basin areas during the LGM; (2) suitable habitat shifted upwards in elevation between the LGM and the present; (3) more ranges have suitable habitat than are currently occupied; and (4) these species are currently restricted to suitable habitats at higher‐elevation range areas. We also examine whether and how much distributional response varies among these montane mammal species. Location The Great Basin of western North America. Methods We re‐examine the past and present distributions of 13 Great Basin montane mammals using ecological niche modelling techniques that utilize now widely available species occurrence data and new, fine‐scale past climatological GIS layers in the present and at the LGM. These methods provide an objective, repeatable means for visual comparison of past and present modelled distributions for species examined in previous biogeographical studies. Results Our results indicate greater areal and lower elevational suitable habitat in the LGM than at present for nearly all montane mammals, and that there is more suitable habitat at present than is currently occupied. Our results also show that lowland areas provide suitable dispersal routes between ranges for most of the montane mammals both at the LGM and at present. However, three of the 13 species have little to no predicted suitable habitat in the LGM near currently occupied ranges, in contrast to the pattern for the other 10. For these species, the model results support more recent long‐distance colonization. Main conclusions Our finding of suitable lowland dispersal routes in the present for most species supports and greatly extends similar findings from single‐species studies. Our results also provide a visually striking confirmation that changes in species distribution and colonization histories of Great Basin montane mammals vary in a fashion related to the tolerances and requirements of each of these species; this has previously been hypothesized but not rigorously tested for multiple montane mammals in the region. 相似文献
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Recent studies have increasingly implicated deep (pre-Pleistocene) events as key in the vertebrate speciation, downplaying the importance of more recent (Pleistocene) climatic shifts. This work, however, has been based almost exclusively on evidence from molecular clock inferences of splitting dates. We present an independent perspective on this question, using ecological niche model reconstructions of Pleistocene Last Glacial Maximum (LGM) potential distributions for the Thrush-like Mourner (Schiffornis turdina) complex in the neotropics. LGM distributional patterns reconstructed from the niche models relate significantly to phylogroups identified in previous molecular systematic analyses. As such, patterns of differentiation and speciation in this complex are consistent with Pleistocene climate and geography, although further testing will be necessary to establish dates of origin firmly and unambiguously. 相似文献
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叶面积指数(Leaf Area Index,LAI)是重要的植被结构参数,调控着植被与大气之间的物质与能量交换,在生态环境脆弱的我国西北部开展植被LAI的研究对阐明该地区植被对气候变化和人类活动的响应特征具有重要的科学意义.利用LAI-2200和TRAC仪器观测了新疆喀纳斯国家级自然保护区森林和草地的有效叶面积指数(LAIe)和真实LAI,构建了其遥感估算模型,生成了研究区LAIe和LAI的空间分布图.在此基础上,分析了LAI随地形因子(海拔、坡度、坡向)的变化特征,探讨了将其应用于估算研究区森林生物量密度的可行性,并评估了研究区MODIS LAI产品的精度.结果表明:研究区阔叶林、针阔混交林、针叶林、草地LAIe的平均值分别为4.40、3.18、2.57、1.76,LAI的平均值分别为4.76、3.93、3.27、2.30.LAIe和LAI的高值主要集中分布在湖泊和河流附近;植被LAI随海拔、坡度和坡向的变化表现出明显的垂直地带性的特点.LAI随海拔和坡度的增加呈现先增加后减小的变化趋势,坡向对针叶林和草地LAI的影响明显,但对阔叶林和针阔混交林LAI的影响较弱;森林生物量密度(BD)随LAI增加而线性增加(BD=44.396LAI-25.946,R2=0.83),研究区森林生物量密度平均值为120.3 t/hm2,估算的总生物量为5.0×l06 t;MODIS LAI产品与利用TM数据生成的LAI之间具有一定的相似性(森林R2=0.42,草地R2=0.53),但森林和草地的MODIS LAI产品分别比利用TM数据生成的LAI偏低16.5％和24.4％. 相似文献
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Xiangjun Sun Xu Li Yunli Luo Xudong Chen 《Palaeogeography, Palaeoclimatology, Palaeoecology》2000,160(3-4):301-316
Studies on the dispersal mechanism and source areas of pollen from hemipelagic sediments recovered from the continental slopes of the South China Sea (SCS) reveal that vegetation existed on the exposed shelves at the Last Glacial Maximum (LGM) and the latter part of the Marine Isotope Stage 3. At the low sea level stand, Artemisia-dominated grassland covered the northern continental shelf and tropical lowland rainforest and mangroves grew on the southern shelf ‘Sunda Land’. Consequently, the climate in the northern SCS must have been much colder and drier during the last glacial period compared to the present. Sunda Land experienced only a marginally lower temperature but was not drier than today. The enhanced contrast between the northern and southern parts of the SCS in vegetation and climate during the LGM may be ascribed, at least partly, to the strengthening of Winter Monsoon during the last glacial period. 相似文献
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叶面积指数（Leaf Area Index,LAI）是定量陆地生态系统中光合作用、呼吸作用、蒸腾、碳和养分循环等过程中物质与能量交换的重要结构参数。目前大、中尺度的气候和生态水文建模使用的LAI产品主要来源于中分辨率成像光谱仪（MODIS）,但由于其反演过程中的不确定性因素导致MODIS LAI产品在部分地区存在质量问题。以青海省复杂植被地区为研究区域,基于实地考察与采样验证了区域内MODIS LAI所存在的质量问题分布,并揭示了不确定因素的影响。与此同时,提出了一种基于PROSAIL模型与深度神经网络（DNN）的混合建模技术,针对MODIS LAI生成机制中地表分类数据、地表反射率数据和反演算法的不确定性进行改进,并基于青海省大范围实测LAI数据评估了改进前后产品的准确度,实测数据的验证结果发现：改进模型的LAI准确度（RMSE=0.48,R2=0.64）显著高于MODIS LAI （RMSE=0.71,R2=0.56）,预测结果与实测结果之间的偏差显著减少;区域尺度上,柴达木荒漠植被低覆盖典型区域、三江源高寒草甸中覆盖典型区域与青海湖牧场草地高覆盖典型区域的RMSE分别提高了0.19、0.10、0.54,改进方法有效解决了MODIS LAI产品中高覆盖植被饱和效应导致的高估以及低覆盖植被未检索导致低估的质量问题,改进结果分布连续,更符合真实植被状况。基于以上研究,充分证明了研究方法对MODIS LAI产品的改进具有可靠性,能够在缺少实测样本数据的情况下有效提高MODIS LAI的质量,为全球植被环境监测与生态建模提供重要的数据支持。 相似文献
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青藏高原是我国的生态安全屏障。气候变化和人类活动背景下,青藏高原植被变化显著,整体呈\"变绿\"之势。然而,前人关于全球尺度的植被变化研究发现,不同卫星遥感产品得到的叶面积指数(LAI)之大小和变化趋势皆存在较大差异。因此,揭示青藏高原植被时空变化格局的不确定性,不仅是科学评估寒区生态系统如何响应气候变化的前提,还可为未来减小对地卫星观测误差提供参考。据此,研究聚焦青藏高原植被条件较好的东部河源区,揭示三种长时间序列LAI数据产品(GIMMS、GLASS和GLOBMAP)在表征LAI多年均值和变化趋势的异同。就多年均值而言,研究区内三种LAI产品的相对不确定性达到26.19%;在生长季三个阶段中,生长季初期的相对不确定性最大,为32.7%。就1982-2018年间的变化而言,GLOBMAP和GLASS相对增大了25.05%和20.24%,而GIMMS 的相对变化仅为3.85%,亦即GLOBMAP和GLASS的\"绿化\"现象最为明显。对1982-2018年间整个生长季、生长季初期和中期的LAI而言,三种产品变化方向不完全一致的面积占研究区总面积的60%,这一面积比例在生长季末期甚至超过了75%。在各下垫面类型中,草原的LAI相对不确定性最大,平均为37.7%;而森林LAI变化方向不完全一致的比例最大,超过了森林总面积的60%。在缺少大面积实测LAI地面\"真值\"的情况下,虽然并未揭示具体何种LAI产品精度最高,但结果对学术界有重要启示:在研究植被变化对生态、水文和气候之影响时,需谨慎使用某单独的LAI产品,否则可能得到相反的科学认知。在未来高分辨率卫星观测和人工智能等先进手段的辅助下,LAI产品的不确定性有望进一步减小,这需要遥感、测绘、生态、地理等多学科的共同努力。 相似文献
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确定土壤水分的植被承载力是我国北方半干旱地区合理调控土壤水分和植被生长关系、科学恢复林草植被的核心问题。我国北方半干旱地区的土壤水分主要来自大气降水, 作为土壤水分限制型生态系统的坡面植被, 植物种类和植被密度等结构特征与降水量紧密相关。根据六盘山石质山区的特点, 基于水量平衡原理, 建立了阴坡华北落叶松(Larix principis-rupprechti)和阳坡草地的土壤水分植被承载力数学模型, 即由4~10月的生长季降雨量(P)计算得到可承载的叶面积指数(Leaf area index, LAI)公式: LAItree= exp((0.773 1×P-186.12)/146.46)和LAIgrass= exp((0.511 2×P-345.93)/227.89), 并提出了考虑坡面水分再分配影响的不同坡位的土壤水分植被承载力计算方法。阴坡华北落叶松的植被承载力(用LAI表示)从坡顶的1.45升高到坡中的4.83, 然后稳定在3.0~3.3。对于阳坡草地, 土壤水分可承载的LAI从坡顶的0.37上升到坡中的0.46, 然后在0.41~0.47之间变动, LAI的计算值与实测值较为接近, 计算结果比较合理。 相似文献
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植被降水利用效率(precipitation-use efficiency, PUE)是评价干旱、半干旱地区植被生产力对降水量时空动态响应特征的重要指标。该研究利用光能利用率CASA (Carnegie-Ames-Stanford Approach)模型估算了2001-2010年内蒙古地区植被净初级生产力(net primary productivity, NPP), 结合降水量的空间插值数据, 分析了近10年内蒙古地区植被PUE的空间分布、主要植被类型的PUE,及其时空格局的驱动因素。结果表明: 2001-2010年内蒙古地区所有植被的平均PUE为0.94 g C·m-2·mm-1, 且在105-120° E地带性规律明显,PUE上升速率为每10° 0.55 g C·m-2·mm-1。各植被类型间PUE差别较大, 其中灌丛PUE最高, 荒漠PUE最低。在不同的降水量区域, 植被PUE的空间分布与气候因子的关系有较大差别, 0-75 mm降水量区间内, PUE随降水量、气温的升高显著下降(R2 = 0.226, p < 0.05); 175-300 mm降水量区间内, 植被 PUE的空间变化与降水量和气温呈极显著相关关系(R2 = 0.878, p < 0.001), 且随降水量的增加显著上升( R2 = 0.94, p < 0.001), 变化速率约为每100 mm降水0.57 g C·m -2·mm-1; 在降水量大于475 mm的区域, 植被PUE的空间分布与降水量、气温的相关性显著(R2 = 0.19, p < 0.05), 且随着气温的上升、降水量的下降而增加, 其中气温的贡献是降水量的8.61倍。在不同的降水量区域, 植被 PUE的年际波动与气候因子的关系也有较大差别, 对于年降水量0-220 mm的地区, PUE的年际波动与降水量呈正相关性、与气温呈负相关性; 在年降水量为220-310 mm的地区, PUE的年际波动主要受降水量的控制, 受气温影响较小; 在年降水量>310 mm的地区,PUE的年际波动与降水量、气温均呈正相关关系, 但在降水量越高的地区, PUE的年际波动与降水量的相关性越弱, 与气温的相关性越强。植被覆盖度与PUE的空间分布极显著相关(R2 = 0.73, p < 0.001), 且与 PUE的年际波动也存在线性相关关系(R2 = 0.11, p < 0.001); 叶面积指数( LAI)与PUE的年际波动呈线性相关关系(R2 = 0.42, p < 0.001), 而当 LAI < 3.15时, PUE的空间分布随LAI增加而呈线性增加。 相似文献
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20世纪80年代以来东亚飞蝗在我国再度猖獗危害,及时、准确地监测东亚飞蝗的危害状况,对于东亚飞蝗的有效防治有重要意义.以河北省黄骅市为研究区,从光学模型的建立机理为着眼点,定量分析和对比了4种由植被冠层孔隙度反演LAI的算法.结果表明,LAI与植被指数之间呈明显的正相关关系,即随着LAI的增大,植被指数也在增大;在4种估算方法中,LAI-2000算法最适用于研究区植被LAI的估算.此外,还分析了LAI与飞蝗发生面积的关系,发现两者呈负相关.并在此基础上建立了飞蝗发生面积的预测模型,即：ALO=-aln（LAI）＋b,其中,a、b为调节系数. 相似文献
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The Sumiaoyuantou locality in Gansu Province was discovered during archaeological survey. Thousands of lithics are distributed in a lens of 1.3m long and 0.13m thick in the Malan loess on the first terrace of the Zhangma River. An assemblage of 2318 fragments of artifacts was obtained by collecting from the profile(2166) and surface(48) in 2002 and 2004, only 2214 of which are reported here. This assemblage is dominated by flakes, shatters and debitage with a few cores and tools. The stone tool technology employed in this locality is mainly bipolar percussion,plus little edge percussion. The main raw material is quartz cobbles from the modern riverbed or the bottom gravel layer. Radiocarbon dates and paleoenvironmental reconstruction shows that the climate changed much during the period 30-15ka BP in the study region. From 30ka to 24ka BP,the climate was warm and humid due to a strong summer monsoon. From 24ka to 18ka BP, it became dry and cold with a decrease in the summer monsoon and an increase in the winter monsoon. From 18ka to 15ka BP, the climate ameliorated a little with the slightly recovered summer monsoons. Sumiaoyuantou represents the late Paleolithic culture in this region, with human activity occurring at the coldest and driest time, the Last Glacial Maximum, 24-18ka BP, which may suggest the high adaptative ability of humans. 相似文献
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Lovelock CE Ball MC Choat B Engelbrecht BM Holbrook NM Feller IC 《Plant, cell & environment》2006,29(5):793-802
Spatial gradients in mangrove tree height in barrier islands of Belize are associated with nutrient deficiency and sustained flooding in the absence of a salinity gradient. While nutrient deficiency is likely to affect many parameters, here we show that addition of phosphorus (P) to dwarf mangroves stimulated increases in diameters of xylem vessels, area of conductive xylem tissue and leaf area index (LAI) of the canopy. These changes in structure were consistent with related changes in function, as addition of P also increased hydraulic conductivity ( K s ), stomatal conductance and photosynthetic assimilation rates to the same levels measured in taller trees fringing the seaward margin of the mangrove. Increased xylem vessel size and corresponding enhancements in stem hydraulic conductivity in P fertilized dwarf trees came at the cost of enhanced midday loss of hydraulic conductivity and was associated with decreased assimilation rates in the afternoon. Analysis of trait plasticity identifies hydraulic properties of trees as more plastic than those of leaf structural and physiological characteristics, implying that hydraulic properties are key in controlling growth in mangroves. Alleviation of P deficiency, which released trees from hydraulic limitations, reduced the structural and functional distinctions between dwarf and taller fringing tree forms of Rhizophora mangle . 相似文献
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Franklin O 《The New phytologist》2007,174(4):811-822
Despite the abundance of experimental data, understanding of forest responses to elevated CO2 is limited. Here I show that a key to previously unexplained production and leaf area responses lies in the interplay between whole-plant nitrogen (N) allocation and leaf photosynthesis. A simple tree growth model, controlled by net growth maximization through optimization of leaf area index (LAI) and plant N, is used to analyse CO2 responses in both young, expanding and closed, steady-state canopies. The responses are sensitive to only two independent parameters, the photosynthetic capacity per leaf N (a) and the fine-root N:leaf N ratio. The model explains observed CO2 responses of photosynthesis, production and LAI in four forest free air CO2 enrichment (FACE) experiments. Insensitivity of LAI except at low LAI, increase in light-use efficiency, and photosynthetic down-regulation (as a result of reduced leaf N per area) at elevated CO2 are all explained through the combined effects on a and leaf quantum efficiency. The model bridges the gap between the understanding of leaf-level and plant-level responses and provides a transparent framework for interpreting and linking structural (LAI) and functional (net primary production (NPP):gross primary production (GPP) ratio, light-use efficiency, photosynthetic down-regulation) responses to elevated CO2. 相似文献
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