Pollen Assemblages of the Human Disturbed Vegetation in Arid and Semi-arid Northwestern China and Its Preliminary Application
|Keywords||Palynology The northwest arid , semi- arid areas Intensity of human activities Surface pollen assemblages PCA analysis Agricultural activities|
Existing surface pollen studies have an important contribution to the reconstruction of the ancient vegetation, ancient climate, but mainly less affected by human activities, natural vegetation, climate and environmental change is the result of both natural factors and human activities must focus on labor and human disturbance vegetation to extract ecological information reflects human activity, This is not only conducive to the recovery of ancient vegetation and paleoclimate, and will make predicting future climate and environmental changes gradually trend on improving. Northwest China arid, semi-arid areas of the fluctuations in the global climate response strong, has always been the hot zone of the global change research. The region showing the oasis in the Gobi desert mosaic the complex geomorphic characteristics of human activities on terrestrial ecosystems affect relatively small areas, topsoil vegetation pollen in the region to study different human activities that can detect human activities in the initial stages of strength under the influence of natural and artificial disturbance and artificial vegetation pollen assemblages characteristic of human activities on the strength of the vegetation, the environment, and to explore. 73 table on samples collected in northwest arid regions, and is located in the middle reaches of the Heihe River in Hexi Corridor Linze wetland profile samples collected from 27 boreholes, trying to take advantage of the area Surface pollen assemblages to reveal the Hexi Corridor region early human activities affect the strength of local vegetation and land use situation. Pollen analysis of surface soil samples, the results show that the emergence of the crop pollen as reveal a sign of human activity, but the level of pollen and pollen assemblages combined to reflect the size of a standard human activity intensity: the intensity of human activities regional pollen assemblages crop pollen, but does not account for the major advantage of its pollen assemblages often reflect vegetation composition profile of the farmland around the area; artificial vegetation and natural vegetation in the transition zone, and that human activities relative strength has been the decline in area , herbal pollen, the pollen assemblages mainly increase in shrub pollen, containing a small amount of crop pollen; belonging to the natural vegetation of the alpine meadow grassland pollen assemblages basically consistent with local vegetation combination Overview wet herb sedge , cold wet type Gramineae mainly xerophytic herbaceous pollen is very low; weak the desert Gobi human activities affect single pollen types most xeric vegetation Chenopodiaceae, ephedra based, low wet herb pollen to Artemisia. The same type but located in different regions or different altitude farmland, the percentage of its crop pollen and pollen assemblages entire sample point may be related to the environment of local vegetation and crop rotation. Intensity of human activity samples (farmland) vegetation cover up to 100%, the humidity is relatively high, but the concentration was lower (average 7341 / g), which may change the soil pH and applied chemistry organic fertilizer affect pollen preservation artificially reduce weed pollen removal of weeds, crop pollen low pollen production and pollination, and other factors related; higher pollen concentrations of natural and artificial vegetation transition zone may have a certain pollen richness and pollen concentration relationship; alpine meadow grassland areas, vegetation cover and pollen concentration is high; Gobi desert in northwest arid area the same vegetation type, tip coverage low sample point, high pollen concentration but this bite can related to the sampling location, season, and desert plants (mainly Chenopodiaceae and Ephedra) high pollen production. PCA analysis the sample permutation graph can distinguish good district of samples of different intensity of human activities under the influence of vegetation types, families and genera Sort figure shows that the first and second sort axis may be related to moisture and temperature, respectively, shows in drought the effects of moisture and temperature on plant growth, and also reflects the most important factors that affect the intensity of human activities should be moisture in the larger context of high temperature. The the Linze wetlands drilling pollen analysis results show that: about 1120a BP (about AD 830, during the late Tang dynasty) to 400 a BP (ca. 1550, that at this stage of the Ming Dynasty, the interim) palynological assemblages natural Wo mainly undergraduate and Asteraceae the Chenopodiaceae occupy a certain content, Artemisia less, rarely crop pollen is stable wetland meadow environment in the region was relatively poor, agricultural activities; fire about 400 a BP ( about the year 1550, that is after the Ming Dynasty interim), Pollen assemblage shows decrease in tree pollen appeared the artificial grass family and a small amount of marijuana pollen, Chenopodiaceae, Lei genus Asteraceae and Gramineae herbs began to expand, may reflect this stage in the Hexi Corridor generation of agricultural re-start the development of people-scale agricultural production activities increase.