A Test of the Vegetation Mosaic Hypothesis: A Hypothesis to Explain the Decline and Extinction of Australian Mammals

The vegetation mosaic hypothesis suggests that medium-sized mammals occupying arid and semi-arid areas of Australia require a habitat that is a fine-grained mosaic of different vegetation types or seral stages. This mosaic is believed to have been created in the spinifex deserts of central Australia by Aboriginal burning practices. Its loss in the period 1940–1960 is postulated to be a primary reason for both major reductions in range and mainland extinctions of many species of medium-sized mammals at this time. This study measured the responses of three species of medium-sized mammals to vegetation patterns within spinifex grasslands that ranged from comparatively uniform to highly diverse. The abundance, condition, and reproductive status of golden bandicoots (Isoodon auratus) , northern brush-tailed possums (Trichosurus vulpecula arnhemensis) , and burrowing bettongs (Bettongia lesueur) were assessed within vegetation mosaics of various scales on Barrow Island, off the northwest coast of Australia. Scale of mosaic proved to have no significant effect on the numbers, condition, or reproductive status of any of the three species. Similarly, the creation of fine-grained mosaics of early seral-stage vegetation mixed within climax vegetation by extensive oil-field operations over nearly half the island had no significant effect on the number or condition of animals. Hence, scale of mosaic seems unlikely to be related to the mainland decline or extinction of these species. The pattern of decline and extinction on the mainland but continued survival on offshore islands is more consistent with the presence (mainland) or absence (islands) of introduced predators (foxes and cats) and herbivores (rabbits and stock).     

Integrated models to support multiobjective ecological restoration decisions

Many objectives motivate ecological restoration, including improving vegetation condition, increasing the range and abundance of threatened species, and improving species richness and diversity. Although models have been used to examine the outcomes of ecological restoration, few researchers have attempted to develop models to account for multiple, potentially competing objectives. We developed a combined state‐and‐transition, species‐distribution model to predict the effects of restoration actions on vegetation condition and extent, bird diversity, and the distribution of several bird species in southeastern Australian woodlands. The actions reflected several management objectives. We then validated the models against an independent data set and investigated how the best management decision might change when objectives were valued differently. We also used model results to identify effective restoration options for vegetation and bird species under a constrained budget. In the examples we evaluated, no one action (improving vegetation condition and extent, increasing bird diversity, or increasing the probability of occurrence for threatened species) provided the best outcome across all objectives. In agricultural lands, the optimal management actions for promoting the occurrence of the Brown Treecreeper (Climacteris picumnus), an iconic threatened species, resulted in little improvement in the extent of the vegetation and a high probability of decreased vegetation condition. This result highlights that the best management action in any situation depends on how much the different objectives are valued. In our example scenario, no management or weed control were most likely to be the best management options to satisfy multiple restoration objectives. Our approach to exploring trade‐offs in management outcomes through integrated modeling and structured decision‐support approaches has wide application for situations in which trade‐offs exist between competing conservation objectives.     

Vehicle-Induced Lead and Cadmium Contamination of Roadside Soil and Plants in Italy

Lead and cadmium concentrations in spontaneous vegetation and in soil sampled at various distances (0–208 m) from several motorways throughout Italy were measured. Lead and cadmium concentrations appear to be correlated to distance from the motorway and to traffic levels. A comparison with data from a remote and unpolluted site shows that foliar lead concentrations can be up to 40 times higher, and foliar cadmium concentrations up to 3 times higher. Plants behave differently in their accumulation of lead and cadmium; conifers present the highest levels. Also the various receptors and compartments of the roadside ecosystem differ in their accumulation of lead and cadmium; soil and bark have consistently higher concentrations, while the leaves and twigs of trees have consistently lower levels. the data recorded by ad hoc introduced bio-accumulating plants (Lolium multiflorum L.) are consistent with those of the spontaneous vegetation. the concentrations of both lead and cadmium in Lolium vary from June to November, following in part the fluctuation in traffic density.     

Response of vegetation and soil ecosystem to mowing and sod removal in the coastal dunes ‘Zwanenwater’, the Netherlands

This paper investigates the effects of mowing and sod removal on vegetation, soil mesofauna and soil profile, and the restoration of these features in the years following sod removal. The sampling site is located in a primary wet dune slack in the northern part of the province of North-Holland. The original vegetation is a heathland withEmpetrum nigrum andCalluna vulgaris, underlain by a Gleyic Arenosol with an O, Ah and (B) horizon development. Above-ground, the vegetation in the dune slack has been mown since 1940. The sod was removed from restricted areas in the slack at various times in the past (1980, 1985, 1987 and 1991). All three sources of data point to adaptation to wet conditions after mowing and sod removal. The vegetation of the mown area is related to the vegetation in the original heathland, although some species appear to have disappeared. Below-ground, mowing drastically reduces the number and depth of occurrence of microarthropoda. Restriction of depth applies also to the Enchytraeidae. Soil profile development is restricted to an Ah-AC-Cr sequence. Species diversity both above and below-ground is relatively high in plots where the sod has recently been cut, due to the rapid colonization by the first pioneer species. A time series for the vegetation is difficult to establish because hydrological conditions interfere with years since sod removal. Soil profile evolution after sod cutting is poor but consistent, from an AC-Cr sequence since 1991, to an O-Ah-Cr sequence since 1980. The management practices were set up with the intention to interrupt the succession to give pioneer species a chance. Neither the vegetation, nor the soil fauna or soil profile have fully recovered during the 13 yr since the first sod removal. So the goal has been reached.     

The Biodiversity Integrity Index: An Illustration Using Ants in Western Australia

Although Western Australia is a relatively unpopulated region, considerable areas of native vegetation have been modified by agricultural clearing, rangeland grazing, urbanization, road construction, and mining. Ant diversity is reduced and community composition changed by each of these land uses. Road construction has the greatest long-term effect on the alpha diversity of ants, followed by agricultural clearing, mining, urbanization, and rangeland grazing. We present data on the extent of these various land uses in each major Western Australian vegetation association. Then, examples of ant diversity and community composition for each land use are coupled with geographic information system data on the extent of each land use in the various vegetation associations to calculate indices of "biodiversity integrity." The extent of biodiversity integrity in each region concurs with a subjective opinion of the condition of each unit. Agricultural clearing, followed by rangeland grazing, were found responsible for the greatest loss of ant biodiversity integrity. The findings relate to Australia in general and may serve as a framework for estimating losses of biodiversity integrity in other regions of the world in taxa other than ants.     

Use of an Airborne Lidar System to Model Plant Species Composition and Diversity of Mediterranean Oak Forests

Abstract: Airborne lidar is a remote‐sensing tool of increasing importance in ecological and conservation research due to its ability to characterize three‐dimensional vegetation structure. If different aspects of plant species diversity and composition can be related to vegetation structure, landscape‐level assessments of plant communities may be possible. We examined this possibility for Mediterranean oak forests in southern Portugal, which are rich in biological diversity but also threatened. We compared data from a discrete, first‐and‐last return lidar data set collected for 31 plots of cork oak (Quercus suber) and Algerian oak (Quercus canariensis) forest with field data to test whether lidar can be used to predict the vertical structure of vegetation, diversity of plant species, and community type. Lidar‐ and field‐measured structural data were significantly correlated (up to r= 0.85). Diversity of forest species was significantly associated with lidar‐measured vegetation height (R²= 0.50, p < 0.001). Clustering and ordination of the species data pointed to the presence of 2 main forest classes that could be discriminated with an accuracy of 89% on the basis of lidar data. Lidar can be applied widely for mapping of habitat and assessments of habitat condition (e.g., in support of the European Species and Habitats Directive [92/43/EEC]). However, particular attention needs to be paid to issues of survey design: density of lidar points and geospatial accuracy of ground‐truthing and its timing relative to acquisition of lidar data.     

1982-2006年华北植被覆盖变化及其与气候变化的关系

利用1982-2006年GIMMSNDVI数据反映华北地区植被覆盖变化状况,结合1982--2006年该地区85个气象站点的气温和降水数据,分别从年际变化、季节变化和月变化三个时间尺度分析华北地区植被覆盖变化及其与气候变化的关系。结果表明,从年际变化来看,华北植被变化与气温变化关系较与降水关系密切;从季节变化来看,华北地区植被生长在不同季节对水热条件变化的响应不同,春季和秋季植被生长与气温的关系较与降水的关系密切,而夏季植被生长主要受降水的影响;从月变化来看,4月和5月植被变化受气温变化影响较明显,一定程度上说明4月和5月植被生长的NDVI值增加可能是由于气候变暖引起的植被生长季提前产生的;6-9月植被生长与前2个月降水变化关系密切,说明植被生长对降水变化具有一定的滞后性。     

Effects of human activities (raking,scraping, off-road vehicles) and natural resource protections on the spatial distribution of beach vegetation and related shoreline features in New Jersey

This study examined the relative impacts of different human activities and natural resource protections on the spatial distribution of beach vegetation and related habitat features (wrack, dune succession) in New Jersey (USA). Field surveys of the 209-km shoreline categorized beach segments according to vegetation cover classes, human activities, protection measures (exclosures, beach management plans, access restrictions) and ownership status (federal, state, etc.). A partition model (classification tree) was used to confirm the relative dominance hierarchy of human actions on the distribution of beach vegetation observed, and quantitative comparisons of dominant activities were conducted using vegetation data collected on 218 transects. The spatial extent of beach vegetation was found to be severely restricted by human activities when unconstrained by resource protections. The greatest reductions were found to result from mechanical raking (?99 %), scraping (?91 %) and all-year recreational ORV use (?86 %), which were dominant on nearly 70 % of the state shoreline. Beaches containing larger areas of vegetation (>5 m) were concentrated in areas with resource protections of various kinds (99 %), and on federal or other public parklands (68 %). Exclosures resulted in the greatest coverage of vegetation (48 % of beach surface) compared to public access restricted areas (41 %), beach management plans (31 %), government-only ORV use (31 %), and off-season recreational ORVs (15 %). Greater protection and recovery of beach vegetation and habitat is needed for species conservation and erosion protection in New Jersey and other coastal environments where these activities occur.     

半干旱区人工封育草场植物群落物种多样性与复杂性研究──以宁夏盐池为例

围栏封育促进植被恢复效果研究方法很多,其中通过研究植被的群落特征及物种多样性来阐述恢复状况仍是比较常用和有效的手段,但多样性测度对生物群落的自组织及有序性方面的特征描述欠缺,鉴于此,多样性与复杂性测度结合起来研究群落结构与功能显得更有意义。研究人工封育对植被恢复过程中群落的多样性与复杂性的影响,必然有助于揭示生态恢复过程机理。目前,利用多样性与复杂性测度相结合来对群落结构进行量化研究不多,用于对草原生态系统植物群落结构研究更少。本文通过样地调查,利用多样性和复杂性指数相结合定量研究半干旱区人工封育草场植物群落物种多样性、复杂性随封育年限的变化规律,并对比分析复杂性与物种多样性之间的相关性。结果表明,（1）老封育区、新封育区丰富度指数整体高于对照区,说明封育有利于物种丰富度的增加。但随封育时间的延长,封育区的优势种占据主要的资源空间,丰富度指数降低。长时间封育,草场植被丰富度将发生规律性波动变化,低峰值和高峰值出现频率均约为4~5年/次。老封育区、新封育区的SW、SP多样性指数值大部分也高于对照区,说明封育措施增加草场植被的多样性。物种多样性指数受降水影响显著,当降水量增加或减少时,多样性指数也相应出现增加或减少,但降水影响效应具有一定的滞后性。老封育区、新封育区均匀度变化比较平稳,且指数值高于对照区,说明封育有利于均匀度的增加。（2）老封育区、新封育区总复杂性指数、无序结构复杂性指数值大部分比对照区指数值高,且指数波动相对平稳,说明封育区群落结构比对照区稳定,更适合荒漠草原植被的生长,封育增加了群落总复杂性、无序结构复杂性。封育也提高群落有序结构复杂性,但?     

雅砻江流域生长季植被时空变化特征及对气象因子的响应分析

在全球气候变化背景下,开展植被变化对气象因子的响应研究对流域生态环境保护和水土资源合理利用具有重要的现实意义。以雅砻江流域为研究区,基于1982—2015年GIMMS NDVI数据,首先采用多种数理统计方法揭示生长季NDVI的时空变化特征,基于滞后相关系数法分析NDVI对气象因子的时滞效应,在此基础上建立各像元NDVI与气象因子的主成分回归方程,分析影响NDVI变化的主要气象因子及其贡献率,进而揭示NDVI对各气象因子的响应变化特征。结果表明:雅砻江流域NDVI在年内呈单峰型变化,峰值出现在8月,生长季NDVI年际变化呈不显著下降趋势。流域NDVI自下游向上游逐渐减小,植被退化面积占30%,改善面积占24.28%,中游植被改善和退化面积占比最大,就各植被类型变化而言,针叶林改善比重相对较大,灌丛和草甸退化较为严重。导致流域植被变化的主控气象因子为降水和气温,其对植被变化的贡献率分别为27.68%和26.31%,其中,流域上游及中游北部地区植被变化主要受气象因素影响,中游南部及下游地区植被受气象因子与其他因子(如人类活动)的共同影响。各像元NDVI变化的主控气象因子存在显著差异,降水、平均气温和相对湿度是中上游植被变化的主控气象因子,而降水和日照时数是下游植被变化的主控气象因子。流域植被对各气象因子的响应存在一定的时滞效应,植被对各气象因子滞后响应面积大小顺序为:平均风速>降水>日照时数>平均气温>相对湿度。中上游植被对主控气象因子降水、平均气温和相对湿度的响应主要为当月及滞后1个月;下游植被对主控气象因子降水的响应主要为滞后1个月和滞后3个月,而对主控气象因子日照时数的响应主要为当月。     

Merthyr Mawr: a case study for the assessment of nitrate at humid dunes in England and Wales

Humid dunes in the UK are at risk from nutrient pressures from multiple sources. The Water Framework Directive 2000/60/EC (WFD) requires assessment and identification of these pressures with appropriate measures defined to mitigate against further damage. We discuss the application of nitrate threshold values for the WFD classification, illustrating this with a case study at Merthyr Mawr, South Wales, where ephemeral groundwater discharge from a spring (‘Burrows Well’) sourced within the Carboniferous Limestone, creates a large dune slack. Ecological surveys suggest that the vegetation in this slack was in unfavourable condition, due to high levels of nitrate. Applying the source-pathway-receptor model an investigation was undertaken to improve the conceptual model and assess the significance of damage from groundwater derived nutrients. Results show groundwater nitrate concentrations?~?10 mg/l as NO₃-N feeding the main slack waters. The vegetation survey data shows clear evidence of ecological damage, and the hydrogeological data traces the source of this back to the Carboniferous Limestone aquifer and not the overlying blown sands. Discharging groundwater is the source of the enrichment. Isotopic analysis suggests that the N is derived from inorganic fertilizer and/or atmospheric N. During the first cycle WFD characterisation the unfavourable status of the dunes due to chemical groundwater pressure resulted in a failure of the surrounding groundwater body, which was designated as poor status. The site has been re assessed for the 2nd Cycle WFD characterisation where recently developed nitrate ‘threshold’ values have been applied to assess the significance of damage for groundwater derived nutrients. The surrounding Carboniferous Limestone catchment is complex and could not be sufficiently constrained, thus land management changes could not be targeted. The paucity of historical or repeat vegetation surveys limits our ability to measure change within the dune vegetation and causes difficulties in understanding the impact of multiple pressures.     

Reversed parasite-mediated selection in sticklebacks from eutrophied habitats

Sexual selection is often assumed to increase the viability of populations by increasing the quality of offspring produced. Presently, human-induced environmental changes are altering the process of sexual selection by influencing male–male interactions and female mate choice. Here, we show that increased density of filamentous algae due to eutrophication reverses parasite-mediated selection during reproduction in threespine sticklebacks (Gasterosteus aculeatus). When we manipulated the density of artificial algae in a breeding area in the Baltic Sea, more males nested in dense than in sparse vegetation, but the males in dense vegetation were more parasitized. Interestingly, heavily parasitized males acquired more eggs than less parasitized males in dense vegetation but not in sparse vegetation. The higher probability of reproduction for parasitized males in dense algae growth could be due to impaired visibility relaxing male–male competition or reducing female choosiness. This could favour males in poor condition that often invest more in attracting females than males in good condition. In sparse vegetation, parasitized males may have a lower reproductive success due to intense male–male competition, careful female choice and high predation rate selecting against parasitized males. The results suggest that eutrophication could alter the fraction of the population that reproduces, which could have long-term evolutionary consequences.     

Effects of experimental protocol on global vegetation model accuracy: A comparison of simulated and observed vegetation patterns for Asia

Prognostic vegetation models have been widely used to study the interactions between environmental change and biological systems. This study examines the sensitivity of vegetation model simulations to: (i) the selection of input climatologies representing different time periods and their associated atmospheric CO₂ concentrations, (ii) the choice of observed vegetation data for evaluating the model results, and (iii) the methods used to compare simulated and observed vegetation. We use vegetation simulated for Asia by the equilibrium vegetation model BIOME4 as a typical example of vegetation model output. BIOME4 was run using 19 different climatologies and their associated atmospheric CO₂ concentrations. The Kappa statistic, Fuzzy Kappa statistic and a newly developed map-comparison method, the Nomad index, were used to quantify the agreement between the biomes simulated under each scenario and the observed vegetation from three different global land- and tree-cover data sets: the global Potential Natural Vegetation data set (PNV), the Global Land Cover Characteristics data set (GLCC), and the Global Land Cover Facility data set (GLCF). The results indicate that the 30-year mean climatology (and its associated atmospheric CO₂ concentration) for the time period immediately preceding the collection date of the observed vegetation data produce the most accurate vegetation simulations when compared with all three observed vegetation data sets. The study also indicates that the BIOME4-simulated vegetation for Asia more closely matches the PNV data than the other two observed vegetation data sets. Given the same observed data, the accuracy assessments of the BIOME4 simulations made using the Kappa, Fuzzy Kappa and Nomad index map-comparison methods agree well when the compared vegetation types consist of a large number of spatially continuous grid cells. The results of this analysis can assist model users in designing experimental protocols for simulating vegetation.     

台湾泥岩地区不同刺竹林景观下之土壤与植被变异

台湾西南部泥岩恶地,由于其特殊之土壤,地力流失消耗与区域微气候型态之间的因果循环,在水土保持与景观上形成不易植生绿化的地区及特殊之世界地形。泥岩地区之不同刺林林相之土壤,其林相皆伐后复层植被区土壤性质变异高于其它位置,而其它区之土壤理化性质在时间及空间上之变异不大,可明显区分林相不同之显著差异。不同林相对泥岩地浅层土壤(0~20cm)理化性质的差异,以植物营养元素与植生覆盖因子可充分说明(约占变异范围之62%)。泥岩试区区中移动性物质(交换性钙、钠与镁)明显较少出现在复层林相处区,而易出现于淋洗、冲蚀量较大之刺林相保留区与隔丛择伐区。长效性植物营养元素因子(pH值与有效性磷),因长时间之林相不同,使其较明显趋于复层林相区堆积,并影响地表植生之种类、分布与覆盖情形。0～20cm土壤性质的分布和离子间的移动特性有关,移动性高的钠、镁离子会在冲蚀量高之区域出现,20～40cm土壤性质的分布则和土壤中之母质与植生有关并与因素分析结果相似,其次为可移动性离子的影响,且应用地理统计印证土壤性质在空间之变化,其分布确实与不同林相位置有关,即植生营养元素(pH值、有效性磷)大都朝向复层植被区之趋势。典型相关分析结果,地表覆盖度与入侵植物数量两变量主要系透过第一个典型因素与第二个典型因素而影响到复层植被区之pH值、有机质等土壤理化性质。     

基于Meta分析的土壤呼吸对凋落物输入的响应

凋落物输入是影响土壤呼吸的一个重要因素,然而从国内外目前研究结果来看,土壤呼吸响应凋落物输入的影响因素尚不清楚。利用国内外已发表的30篇研究论文共1393对有效数据,通过Meta分析,从凋落物管理措施、气候、植被、地形、土壤理化性质等因素揭示凋落物输入对土壤呼吸的影响程度。研究发现:与清除凋落物处理相比较而言,(1)凋落物输入后显著增加了土壤呼吸,且土壤呼吸的增加程度呈现出倍增凋落物处理是自然凋落物处理的1.33倍;(2)不同气候条件下的土壤呼吸增加程度呈现出强降雨(>1000 mm)是微弱降雨(<1000 mm)的1.34倍,以及高温气候(>20℃)是低温气候(<20℃)的1.7倍;(3)土壤呼吸的增加程度在不同植被带下呈现出针叶林带(34.1%)>阔叶林带(28%)>混交林带(22%)>草地(17.3%)的趋势;(4)不同海拔梯度条件下土壤呼吸的增加程度呈现出高海拔(59.6%)>中海拔(34.2%)>低海拔(26.7%)的趋势;(5)不同土壤理化性质条件下的土壤呼吸增量呈现出低容重(77.5%)分别是中容重(26.9%)和高容重(18.0%)的2.9倍和4.3倍,同时中性土壤(79.6%)的呼吸增量远远大于酸性(28.2%)和碱性(24.1%)土壤的呼吸增量,以及高土壤碳氮比(81.2%)的土壤呼吸增量远远大于低土壤碳氮比(19.4%)和中土壤碳氮比(29.6%)的土壤呼吸增量。由此可见,凋落物输入后会导致土壤呼吸的显著增加,但是不同气候、不同植被、不同地形、不同土壤理化性质等条件下其土壤呼吸增加的幅度不同。     

Post-fire vegetation regrowth detection in the Deiva Marina region (Liguria-Italy) using Landsat TM and ETM+ data

Obtaining quantitative information about the recovery of fire-affected ecosystems is of utmost importance from the management and decision-making point of view. Nowadays the concern about natural environment protection and recovery is much greater than in the past. However, the resources and tools available for its management are still not sufficient. Thus, attention and precision is needed when decisions must be taken. Quantitative estimates on how the vegetation is recovering after a fire can be of help for evaluating the necessity of human intervention on the fire-affected ecosystem, and their importance will grow as the problem of forest fires, climate change and desertification increases.This article performs a comparison of methods to extract quantitative estimates of vegetation cover regrowth with Landsat TM and ETM+ data in an area that burned during the summer of 1998 in the Liguria region (Italy). In order to eliminate possible sources of error, a thorough pre-processing was carried out, including a careful geometric correction (reaching RMSE lower than 0.3 pixels), a topographic correction by means of a constrained Minnaert model and a combination of absolute and relative atmospheric correction methods. Pseudo Invariant Features (PIF) were identified by implementing an automated selection method based in temporal Principal Component Analysis (PCA), which has been called multi-Temporal n-Dimensional Principal Component Analysis (mT-nD-PCA).Spectral Mixture Analysis (SMA) was compared against quantitative vegetation indices which are based on well known traditional vegetation indices like Normalized Difference Vegetation Index (NDVI) and Modified Soil Adjusted Vegetation Index (MSAVI). Accuracy assessment was performed by regressing vegetation cover results obtained with each method against field data gathered during the fieldwork campaign carried out in the study area. Results obtained showed how vegetation cover fractions extracted from the NDVI based quantitative index were the most accurate, being superior to the rest of the techniques applied, including SMA.     

植被恢复的生态效应研究进展

植被在水土保持、水源涵养及生态系统的固碳过程中起着重要的作用。植被恢复是指运用生态学原理,通过保护现有植被、封山育林或营造人工林、灌、草植被,修复或重建被毁坏或被破坏的森林和其他自然生态系统,恢复其生物多样性及其生态系统功能。目前,植被的自然及人工恢复是改善脆弱生态系统及退化生态系统生态环境现状最有效的措施。植被在恢复过程中对地上植被生态系统,物种多样性的恢复有着重要影响,同时通过凋落物及根系的输入,可以有效改善地下生态系统,增加土壤的养分含量、改善土壤的物理结构、增加土壤生物的生物量及活性。文章以地上及地下生态系统为出发点,综述了植被恢复过程中自然及人工恢复过程中不同的植被类型、不同的恢复时间下植物物种组成和多样性、土壤理化性质及土壤微生物群落的变化。植被的自然及人工恢复在一定程度上均能增加植物物种的多样性,随着恢复年限的增加物种的组成发生改变且多样性呈增加趋势,但一些特殊环境下不当的人工恢复可造成植被演替向退化方向发展,降低生物多样性。不同的植被类型由于其生长方式的不同对土壤理化性质和土壤微生物的影响存在差异,随着恢复年限的增长,土壤理化指标及微生物学指标呈现先增加而后趋于平稳的状态。针对已有的研究进展,提出在未来的研究过程中,一方面应该增加更多的对比研究,对不同环境下,不同的恢复物种,不同的恢复方式进行更深入地探讨;另外一方面应增加不同尺度的研究,现有的研究多集中在样地尺度,未来应在更大尺度上进行分析;再者,地上及地下生态系统之间的相互关系及影响机理一直是土壤学科研究的热点,植被恢复过程中应增加更多该方面的机理研究。     

Modeling seasonal course of carbon fluxes and evapotranspiration in response to low temperature and moisture in a boreal Scots pine ecosystem

Environmental conditions act above and below ground, and regulate carbon fluxes and evapotranspiration. The productivity of boreal forest ecosystems is strongly governed by low temperature and moisture conditions, but the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In order to quantify the seasonal responses of vegetation to environmental factors, the seasonality of carbon and heat fluxes and the corresponding responses for temperature and moisture in air and soil were simulated by merging a process-based model (CoupModel) with detailed measurements representing various components of a forest ecosystem in Hyytiälä, southern Finland. The uncertainties in parameters, model assumptions, and measurements were identified by generalized likelihood uncertainty estimation (GLUE). Seasonal and diurnal courses of sensible and latent heat fluxes and net ecosystem exchange (NEE) of CO₂ were successfully simulated for two contrasting years. Moreover, systematic increases in efficiency of photosynthesis, water uptake, and decomposition occurred from spring to summer, demonstrating the strong coupling between processes. Evapotranspiration and NEE flux both showed a strong response to soil temperature conditions via different direct and indirect ecosystem mechanisms. The rate of photosynthesis was strongly correlated with the corresponding water uptake response and the light use efficiency. With the present data and model assumptions, it was not possible to precisely distinguish the various regulating ecosystem mechanisms. Our approach proved robust for modeling the seasonal course of carbon fluxes and evapotranspiration by combining different independent measurements. It will be highly interesting to continue using long-term series data and to make additional tests of optional stomatal conductance models in order to improve our understanding of the boreal forest ecosystem in response to climate variability and environmental conditions.     

1987-2008年南四湖湿地植被碳储量时空变化特征

利用研究区1987、1997和2008年的LandsatTM／ETM＋卫星遥感数据,结合实地采样调查和收集的资料,计算3个时期山东省南四湖湿地各植被类型的面积和碳储量;同时依照不同覆被类型（植被类型）的平均碳储量将各覆被类型的斑块划分为不同储碳等级,绘制3个时期的南四湖湿地植被碳格局图,分析植被碳储量的时空变化特征、变化产生的原因和变化对湿地的潜在影响。研究结果表明：研究前期（1987年）植被储碳格局存在着明显的植被碳储量以湖南北中心线向两岸增大的带状特征,研究中后期（1997-2008年）带状储碳格局不断破碎化并最终消失。整个研究期高储碳等级的斑块面积不断减小,低储碳等级的斑块面积增加。湿地植被碳储量呈现前期基本稳定后期显著减少的特征,1987、1997和2008年湿地植被碳储量均值分别为1．07、1．08和O．64TgC,1987-1997年湿地植被碳储量平均年增加0．001TgC,变化幅度不大;1997-2008年年减少0．04TgC,下降较明显。其中自然植被碳储量在整个研究期内持续减少,人工植被碳储量呈现先增加后减少的波动变化特征,分析认为这一变化特征产生的主要原因是南四湖地区多因子驱动的土地覆被变化活动。通过区域湿地植被的碳平衡动态分析认为,植被碳储量（碳库）的减少可能会导致整个湿地碳储量的入不敷出,使整个湿地碳汇能力下降甚至可能变为碳源。     

Spectral characteristics of plant communities from salt marshes: A case study from Chongming Dongtan, Yangtze estuary, China

The spectral reflectance of recently formed salt marshes at the mouth of the Yangtze River, which are undergoing invasion by Spartina alterniflora, were assessed to determine the potential utility of remotely sensed data in assessing future invasion and changes in species composition. Following a review of published research on remote sensing of salt marshes, 53 locations along three transects were sampled for paired data on plant species composition and spectral reflectance using a FieldSpec? Pro JR Field Portable Spectroradiometer. Spectral data were processed concerning reflectance, and the averaged reflectance values for each sample were reanalysed to correspond to a 12-waveband bandset of the Compact Airborne Spectral Imager. The spectral data were summarised using principal components analysis (PCA) and the relationships between the vegetation composition, and the PCA axes of spectral data were examined. The first PCA axis of the reflectance data showed a strong correlation with variability in near infrared reflectance and ‘brightness’, while the second axis was correlated with visible reflectance and ‘greenness’. Total vegetation cover, vegetation height, and mudflat cover were all significantly related to the first axis. The implications of this in terms of the ability of remote sensing to distinguish the various salt marsh species and in particular the invasive species S. alterniflora were discussed. Major differences in species with various physiognomies could be recognised but problems occurred in separating early colonising S. alterniflora from other species at that stage. Further work using multi-seasonal hyperspectral data might assist in solving these problems.