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991.
滨海湿地是具有特殊水文、土壤及生物特征的生态系统,蟹类作为其重要生物组成部分,在维护滨海湿地生态系统生物多样性方面具有重要意义。基于2022年6月野外调查数据,结合各环境因子的相关性分析与冗余分析结果,同时构建偏最小二乘结构方程模型,探究蟹类数量分布与关键生境因子之间的关系。结果表明,研究区内的蟹类共有5种,属沙蟹科(Ocypodidae)和方蟹科(Grapsidae),广泛分布于海堤向海一面的潮滩上,数量由陆向海总体减少,双齿近相手蟹(Sesarma bidens)是研究区蟹类的优势种。不同种蟹类生境偏好有所不同,双齿近相手蟹和天津厚蟹(Helice tientsinensis)偏好互花米草(Spartina alterniflora)盐沼,弧边招潮蟹(Uca arcuata)偏好互花米草和碱蓬(Suaeda salsa)混合生境,伍氏拟厚蟹(Helice wuana)偏好碱蓬盐沼,日本大眼蟹(Macrophthalmus japonicus)偏好光滩生境。相关性分析和冗余分析结果表明蟹类数量与植物地上生物量、植被覆盖度、相对高程呈现显著正相关性,与淹水时长呈现显著负相关性。偏最小二... 相似文献
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长江口地区近7000 a来的植被、气候演变研究 总被引:3,自引:0,他引:3
长江三角洲地区的孢粉资料已相当丰富,但崇明岛地区以前孢粉研究资料较少,本文对崇明岛北侧的CY孔作了高分辨率的孢粉研究,详细地划出了大西洋期以来的9个孢粉组合带,并结合邻区钻孔孢粉资料研究,恢复了该区植被、气候演化的7个阶段。从大西洋中期起植被依次为:中亚热带含落叶树的常绿阔叶林;中亚热带北缘常绿阔叶、落叶阔叶混交林;北亚热带北缘以松、栎为主的落叶阔叶、针叶混交林;中亚热带北缘常绿阔叶、落叶阔叶混交林;北亚热带常绿阔叶、落叶阔叶、针叶混交林;北亚热带北缘含常绿阔叶树的落叶阔叶、针叶混交林;北亚热带常绿阔叶、落叶阔叶、针叶混交林。气候经历如下的波动:热暖潮湿—暖热湿润—温和略干—温暖湿润—温暖略湿—温而略干—温暖湿润,其气候波动与世界性的气候变化相一致,而且与海平面变化相吻合,从而为本地区古植被、古气候、古环境的重建提供了丰富的孢粉学资料。 相似文献
995.
A pollen diagram has been produced from the base of the Caburn (East Sussex) that provides a temporally and spatially precise record of vegetation change on the English chalklands during the mid‐Holocene (ca. 7100 to ca. 3800 cal. yr BP). During this period the slopes above the site appear to have been well‐wooded, with vegetation analogous to modern Fraxinus–Acer–Mercurialis communities in which Tilia was also a prominent constituent. However, scrub and grassland taxa such as Juniperus communis, Cornus sanguinea and Plantago lanceolata are also regularly recorded along with, from ca. 6000 cal. yr BP onwards, species specific to Chalk grassland (e.g. Sanguisorba minor). This supports suggestions that elements of Chalk grassland persisted in lowland England through the Holocene. Such communities are most likely to have occupied the steepest slopes, although the processes that maintained them are unclear. Human interference with vegetation close to the site may have begun as early as ca. 6350 cal. yr BP and initially involved a woodland management practice such as coppicing. From the primary Ulmus decline (ca. 5700 cal. yr BP) onwards, phases of limited clearance accompanied by cereal cultivation occurred. Taxus baccata was an important component of the woodland which regenerated between these phases. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
996.
Calvin J. Heusser Thomas V. Lowell Linda E. Heusser Andrs Moreira M. Simn Moreira M. 《第四纪科学杂志》2000,15(2):115-125
Pollen stratigraphy of a core taken from a fen at Fundo Nueva Braunau (40°17.49′S, 73°04.83′W), situated 2 km beyond the western border of Llanquihue‐age glacial drift, spans an age range from an estimated 60 000–70 000 BP to about 14 000 14C yr BP (marine Oxygen Isotope Stages 4–2). The location at present is in the contact zone of Valdivian Evergreen Forest and Lowland Deciduous Beech Forest. Early and late in the pollen record, as indicated by assemblages of southern beech (Nothofagus dombeyi type) and grass (Gramineae), the site was located in Subantarctic Parkland. Intervening assemblages represent expansion of Valdivian–North Patagonian Evergreen Forest (> 49 355 to about 40 000 14C yr BP) and North Patagonian Evergreen Forest–Subantarctic Parkland (approximately 40 000 to 30 000 14C yr BP). Climate over the time span was under the storm regime of the Southern Westerlies and apparently uninterruptedly wet. When Subantarctic Parkland expanded, cold conditions with summer temperatures estimated at 8–9°C (7°C lower than present) resulted in episodes of glacier maxima. Climate moderated during the period of forest expansion, at which time glaciers were in a state of recession. Contrasting with the continuously wet climate of the Lake District for the period of record, climate in semi‐arid–arid, subtropical Chile underwent extended intervals of precipitation. Data from both the terrestrial and marine realm implicate the Southern Westerlies as the cause of intensified storm activity at lower latitudes. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
997.
Xiaoying Chen Lin Chen Xinguo Yang Minlan Li Shuangqi Yang Dian Yu Naiping Song 《水文研究》2024,38(5):e15159
Understanding the water use characteristics and water relationship of coexisting vegetation in a mixed-species plantation of trees and shrubs is crucial for the sustainable restoration of degraded arid areas. This study investigated the water use characteristic of coexisting sand-binding vegetation combinations in the sierozem habitat (Populus przewalskii Maxim namely Populus-S and Caragana liouana) and aeolian sandy soil habitats (Populus przewalskii Maxim namely Populus-A and Salix psammophila) of the desert steppe. By analysing the δ2H and δ18O isotopes in xylem, soil water, groundwater and precipitation, a Bayesian MixSIAR model was employed to quantitatively assess the water utilization characteristics of plants. Throughout the growing season, in the sierozem habitat, C. liouana exhibits the highest efficiency in utilizing soil moisture above 60 cm (53.45%) and displays adaptable water use strategies. In contrast, Populus-A predominantly relies on deep soil moisture below 60 cm plus groundwater (63.89%). In the aeolian sandy soil habitat, both Populus-A and S. psammophila similarly favour deep soil moisture below the 60 cm soil plus groundwater (66.77% and 67.60%, respectively). During the transition period from the dry to the wet seasons, although both Populus-A and S. psammophila in the aeolian sandy soil habitat shifted their water sources from deeper to shallower ones, there was considerable overlap in the water sources used by Populus-A and S. psammophila. This overlap led to competition for water resources and exacerbated the depletion of deep soil moisture in both seasons. Conversely, in the sierozem habitat, the partitioning of water sources between Populus-S and C. liouana facilitated the allocation and utilization of water resources between the two species. The findings highlight the need for species-specific consideration in water resource allocation within mixed-species plantations of trees and shrubs, which is crucial for sustainable vegetation restoration in sand-binding ecosystems. 相似文献
998.
Two pollen records from La Chonta bog (2310 m altitude) and one pollen record of a soil profile (2430 m altitude) at a short distance from the bog permit the reconstruction of the vegetational history and climatic sequence of probably the last ca. 80 000 yr of the Cordillera de Talamanca, Costa Rica. The three pollen records can be correlated on the basis of three radiocarbon-dated horizons (> 39 900 yr BP, 34 850 yr BP and 1390 yr BP) and palynostratigraphy. Pollen concentration data provide indirect time control between radiocarbon-dated horizons of the La Chonta 2 core. During the Early Glacial successive fluctuations of the upper forest line occurred between ca. 2300 m and 2800 m altitude and the bog is alternately situated close to the subalpine rainforest belt and in the uppermontane rainforest belt. During the Pleniglacial (ca. 50 000-13 000 yr BP) the forest line fell to ca. 2000 m altitude and paramo vegetation surrounded the La Chonta site. During the Late Glacial the forest line shifted rapidly in ca. 270 yr to 2700–2800 m altitude and the lake became surrounded by Quercus-dominated upper montane rainforest during a period of ca. 1655 yr. A distinct climate cooling (by 2–2.5°C) followed during ca. 580 yr and the upper forest line dropped to ca. 2400 m altitude. This temperature rebound is probably equivalent to the Younger Dryas event. In the depression extensive Alnus carr and swamp vegetation developed. Finally, during the Holocene, the forest line shifted to 3300–3500 m elevation and the lower montane rainforest reached close to ca. 2300 m altitude. In the later part of the Holocene subparamo scrub with Hypericum, Puya, Compositae, Escallonia and Ericaceae largely replaced Alnus carr and the regional and local vegetation closely resembles the presentday composition. During the Last Glacial to Holocene transition a shift of the upper forest line of ca. 1400 m is inferred, corresponding to a glacial temperature depression at 2300 m altitude of ca. 8°C. 相似文献
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