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1.
Trylee Nyasha Matongera Onisimo Mutanga Timothy Dube Romano Trent Lottering 《国际地球制图》2018,33(3):209-224
Bracken fern is one of the major invasive plants distributed all over the world currently threatening socio-economic and ecological systems due to its ability to swiftly colonize landscapes. The study aimed at reviewing the progress and challenges in detecting and mapping of bracken fern weeds using different remote sensing techniques. Evidence from literature have revealed that traditional methods such as field surveys and modelling have been insufficient in detecting and mapping the spatial distribution of bracken fern at a regional scale. The applications of medium spatial resolution sensors have been constrained by their limited spatial, spectral and radiometric capabilities in detecting and mapping bracken fern. On the other hand, the availability of most of these data-sets free of charge, large swath width and their high temporal resolution have significantly improved remote sensing of bracken fern. The use of commercial satellite data with high resolution have also proven useful in providing fine spectral and spatial resolution capabilities that are primarily essential to offer precise and reliable data on the spatial distribution of invasive species. However, the application of these data-sets is largely restricted to smaller areas, due to high costs and huge data volumes. Studies on bracken fern classification have extensively adopted traditional classification methods such as supervised maximum likelihood classifier. In studies where traditional methods performed poorly, the combination of soft classifiers such as super resolution analysis and traditional methods of classification have shown an improvement in bracken fern classification. Finally, since high spatial resolution sensors are expensive to acquire and have small swath width, the current study recommends that future research can also consider investigating the utility of the freely available recently launched sensors with a global footprint that has the potential to provide invaluable information for repeated measurement of invasive species over time and space. 相似文献
2.
E. Schrank 《International Journal of Earth Sciences》1994,83(4):773-786
A palynological investigation of 164 samples from 18 water wells in northern Kordofan, Sudan, enabled the recognition of five informal zones based on pollen and spore assemblages ranging in age from Albian to Maastrichtian. The youngest (late Campanian-Maastrichtian) assemblages are restricted to the Bagbag Basin, whereas Albian-Cenomanian (to Turonian) sediments are widespread to the east and west of the Bagbag area. Impressions of Salvinia floating leaves from outcrops of the upper Hamrat el Wuz Formation, western part of the study area, are among the oldest occurrences of this water fern and indicate a Campanian-Maastrichtian age for these sediments.The vertical distribution of hygrophilous (pteridophytic spores) versus xerophilous (ephedroids and possibly small, weakly sculptured tricolporates) elements in the palynofloras suggests widespread moist or even aquatic habitats in the Albian-Cenomanian and Campanian-Maastrichtian. A shift towards drier conditions occurred in the late Cenomanian-Turonian. Throughout the Cretaceous, however, there may have been extensive arid/semiarid areas of non-deposition and seasonally dry periods. Some characteristics of the local palynofloras are attributed to its inner continental position. Rare Albian-Cenomanian and Campanian-Maastrichtian dinoflagellates could be interpreted as lacustrine phytoplankton rather than as evidence for marine influence. 相似文献
3.
芒萁是华南退化坡地上最具代表性的先锋种、优势种和关键种,能够快速形成密集的单优种层片结构。与传统阻碍更新的观点不同,野外观察发现芒萁层片内仍有少数物种能够成功定居,被认为具有生态筛效应。文章通过设置4种芒萁层片处理（芒萁层片完全剔除-UR;仅保留地上层-AF;仅保留根毯层-AR;芒萁层片全部保留-CK）,分别在不同处理下移植目标种幼苗并结合土壤性状,探究芒萁层片生态筛效应及其潜在机理。结果发现：1）桉林芒萁根毯层中土壤有机质、全氮、碱解氮、有效磷、速效钾、交换性钠、交换性钙、交换性镁和阳离子交换量均显著高于芒萁红壤层和裸地红壤;2）多数乔木种和草本种在芒萁根毯层保留时无法存活,仅荷木、桃金娘、梅叶冬青和野牡丹等目标种幼苗在保留芒萁根毯层处理（AR和CK）下能够存活与生长。这表明芒萁层片确实具有生态筛效应,且其关键在于根毯层的作用而并非土壤养分改善作用。理论上,芒萁层片（尤其是根毯层）与生态恢复的生物阈值突破密切相关,未来需要进一步解析芒萁根毯层的结构与功能。应用上,华南地区存在大量以芒萁为单优林下植物的人工林类型（如桉林等）,在进行结构优化与林分改造时需注意芒萁的生态筛效应。 相似文献
4.
蕨类植物化石繁殖器官微细构造研究方法及意义 总被引：2，自引：0，他引：2
本文介绍了蕨类植物化石原位繁殖器官微细构造研究的实验技术和方法，讨论了这一研究在蕨类植物化石的分类归属和系统演化研究中的意义． 相似文献
5.
根是植物的重要营养器官,对维持植物生理活动及生态系统物质循环和能量流动极为重要。真蕨类植物的根系以可预测的方式起源于枝,被称为枝生根,通常也被称为不定根。相比于对种子植物根系的广泛研究,对真蕨类植物根系的认识较为薄弱。通过广泛收集各类文献中有关真蕨类根系的信息,以及观察大量化石、现生植物标本,对若干化石及现生真蕨类植物根系的形态学特征进行了综述。在繁盛于中、晚泥盆世的早期真蕨类植物中,密集的枝生根着生于茎轴、或推测的根状茎、或主干膨大的基部上;根系的分枝罕见,若存在,则仅表现为等二歧式分枝;而在真蕨纲冠群植物中,枝生根密集或稀疏,根系呈单轴式分枝,侧根发育,可达2级甚至更多。真蕨类根系统的形态演化可采用“顶枝学说”进行解释: 真蕨类植物的根系具有一定的演化保守性,均为枝生根;早期真蕨类的原始根系可视为不分枝的或偶见二歧式分枝的顶枝束;经历顶枝束的越顶生长,侧根系统在真蕨纲冠群中演化出现。真蕨类根系的构型、形态、解剖结构、生物量分配等信息可在化石记录中得以揭示,这些信息可为探讨植物根系的演化及研究地史时期的植物—土壤系统提供重要依据。最后,简述了这方面研究的1个案例,即北京西山侏罗纪地层中的真蕨类根系化石及根系—土壤系统。 相似文献
6.
中国北方68个不同森林群落表土花粉研究表明,东部森林区森林群落中乔木花粉百分比多数大于30%,草本花粉百分比小于50%;草原区河谷林和低山林带乔木花粉百分比低于30%,草本植物花粉高于50%。松、云冷杉林和桦木林花粉组合中的优势成分也是群落中的优势植物;落叶松林中蒿花粉含量最高,其次为松、落叶松;山杨林中松、桦是最主要花粉类型;栎、胡桃、鹅耳枥及青檀林中,除建群种外,松是最主要的乔木花粉类型,中华卷柏也较多;阔叶杂木林与油松阔叶混交林花粉组成相似,松、桦、中华卷柏是最主要的花粉类型。降趋对应分析、主坐标分析和聚类分析研究表明云冷杉、落叶松和桦林花粉组合及所代表的生境具有一定的相似性,为最耐寒喜湿类型;沙枣、榆树疏林和草原区人工杨树林花粉组合及所代表的生境为最喜干旱类型;山杨林较桦木林略喜暖干,栎林、鹅耳枥林和青檀林较山杨林更喜暖干,胡桃楸林为所有森林类型中最喜暖类型,但喜湿性低于桦木林高于栎林。森林区松蒿比(P/A)大于0.1,草原区松蒿比小于0.1。松林、油松阔叶混交林和阔叶杂木林以高松蒿比、高蕨类与草本比值(F/H)和低蒿藜比(A/C)为特征,云冷杉、落叶松和桦林以低松蒿比、低蕨类与草本比值和高蒿藜比为特征,栎、胡桃、鹅耳枥、杨、青檀等阔叶林以高松蒿比、高蒿藜比和低蕨类与草本比值,可与落叶阔叶杂木林、油松阔叶混交林、松林、桦林和针叶林区分开。但这些比值的可操作性,有待进一步研究。 相似文献
7.
松辽盆地是我国白垩系分布最广、厚度最大、发育最全的陆相沉积盆地。孢粉分析发现桫椤孢在松辽盆地白垩系中比较常见。但由于桫椤孢与桫椤科或者蚌壳蕨科具有亲缘关系。桫椤孢在地层中的发现不能明确表明桫椤科植物的存在。这种状况影响了我们对松辽盆地古环境和古气候的精确分析。白垩纪桫椤科矿化茎干化石在黑龙江省齐齐哈尔市克山县的发现为解决桫椤科植物在松辽盆地存在与否的难题提供了重要证据。该化石为桫椤科树蕨植物的茎干片段,包括髓、网状中柱、皮层。分体中柱的横截面呈U、W或S形,外围具有厚壁组织鞘,分体中柱末端朝向髓部或者皮层。髓和皮层由薄壁组织组成,其中分布有许多维管束和根。创伤组织在髓中常见。当前化石是我国第一个桫椤科茎干化石记录。它的发现表明白垩纪时期松辽盆地北部曾经分布着现今多生长于热带、亚热带的桫椤科树蕨祖先类群。结合与其伴生的一些登普斯基树蕨、本内苏铁茎干等化石证据,可能指示当时气候为热带或者亚热带。 相似文献
8.
Twenty-nine megaspore species including six new taxa (Bacutriletes otwayensis sp. nov.,Erlansonisporites cerebrus sp. nov., Erlansonisporites decisum sp. nov., Hughesisporites coronatus sp. nov., Hughesisporites dettmanniae sp. nov., and Verrutriletes depressus sp. nov.) are documented from Aptian and Albian strata of the Gippsland and Otway basins, southeastern Australia. Together with six taxa known only from underlying Neocomian strata, these megaspores are used to establish four provisional biozones for the Lower Cretaceous that complement existing biostratigraphic schemes based on miospores and plant macrofossils. Megaspores are best represented in silty floodbasin facies and it is likely that the parent plants predominantly occupied moist understorey to fully aquatic habitats on the floodplain. Megaspores are sparsely represented in most other fluvial facies chiefly due to reworking of floodbasin sediments into higher energy channel and crevasse deposits. The relatively high diversity of lycophyte and fern megaspores contrasts with the scarcity of these plant groups in macrofossil assemblages. The megaspore record suggests that heterosporous cryptogams may have been significantly more prominent in the vegetation of this region than previously suggested. Several megaspores from southeastern Australia are closely comparable to forms from India and Argentina indicating broad similarities between Early Cretaceous heterosporous fern and lycophyte communities across Gondwana. These similarities also suggest that megaspores may be useful for inter-continental biostratigraphic correlation. 相似文献
9.
Bracken fern is an invasive plant that presents serious environmental, ecological and economic problems around the world. An understanding of the spatial distribution of bracken fern weeds is therefore essential for providing appropriate management strategies at both local and regional scales. The aim of this study was to assess the utility of the freely available medium resolution Landsat 8 OLI sensor in the detection and mapping of bracken fern at the Cathedral Peak, South Africa. To achieve this objective, the results obtained from Landsat 8 OLI were compared with those derived using the costly, high spatial resolution WorldView-2 imagery. Since previous studies have already successfully mapped bracken fern using high spatial resolution WorldView-2 image, the comparison was done to investigate the magnitude of difference in accuracy between the two sensors in relation to their acquisition costs. To evaluate the performance of Landsat 8 OLI in discriminating bracken fern compared to that of Worldview-2, we tested the utility of (i) spectral bands; (ii) derived vegetation indices as well as (iii) the combination of spectral bands and vegetation indices based on discriminant analysis classification algorithm. After resampling the training and testing data and reclassifying several times (n = 100) based on the combined data sets, the overall accuracies for both Landsat 8 and WorldView-2 were tested for significant differences based on Mann-Whitney U test. The results showed that the integration of the spectral bands and derived vegetation indices yielded the best overall classification accuracy (80.08% and 87.80% for Landsat 8 OLI and WorldView-2 respectively). Additionally, the use of derived vegetation indices as a standalone data set produced the weakest overall accuracy results of 62.14% and 82.11% for both the Landsat 8 OLI and WorldView-2 images. There were significant differences {U (100) = 569.5, z = −10.8242, p < 0.01} between the classification accuracies derived based on Landsat OLI 8 and those derived using WorldView-2 sensor. Although there were significant differences between Landsat and WorldView-2 accuracies, the magnitude of variation (9%) between the two sensors was within an acceptable range. Therefore, the findings of this study demonstrated that the recently launched Landsat 8 OLI multispectral sensor provides valuable information that could aid in the long term continuous monitoring and formulation of effective bracken fern management with acceptable accuracies that are comparable to those obtained from the high resolution WorldView-2 commercial sensor. 相似文献
10.
北岔沟砂岩为华北地台二叠系山西组与太原组划分对比的主要标志层,在鄂尔多斯盆地呈大面积连片分布,是上古生界重要的天然气储集层。依据地面露头调查结果与勘探资料,结合前人有关古构造和岩相古地理研究成果,笔者对鄂尔多斯盆地北岔沟砂岩的沉积特征进行了详细分析。结果表明,受益于物源区大量高石英含量的粗碎屑物质在短时间内的集中供应,北岔沟砂岩在地层中位置稳定,以含砾粗粒石英砂岩为主,石英含量高达90%左右,砂体叠置紧密,单砂体之间很少见泥岩隔夹层。这些砂体分别隶属于冲积扇、砾质辫状河和辫状河三角洲沉积体系,在鄂尔多斯盆地北部高、南部次高、中南部低的古地理背景控制下,由盆地南、北边缘向中部依次推进,沉积中心区以北发育4个规模宏大的三角洲沉积主砂带,以南发育6个规模较小的主砂带。受各主砂带砂体规模、矿物组分含量及其成岩作用差异影响,各砂带的储集物性具有较大变化,其中砂体规模最大、石英含量最高、长石等易溶矿物在酸性地层水作用下溶蚀彻底的杭锦旗—榆林—子洲—清涧—永和—吉县主砂带,储集能力最好,最有利于天然气的大规模聚集成藏,是鄂尔多斯盆地北岔沟砂岩天然气进一步勘探开发的有利场所。 相似文献