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首页> 外文学位 >Great Basin vegetation response to groundwater fluctuation, climate variability, and previous land cultivation: The application of multitemporal measurements from remote sensing data to regional vegetation dynamics.
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Great Basin vegetation response to groundwater fluctuation, climate variability, and previous land cultivation: The application of multitemporal measurements from remote sensing data to regional vegetation dynamics.

机译：大盆地植被对地下水波动，气候变化和先前耕地的响应：从遥感数据到区域植被动态的多时相测量的应用。

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The conversion of large natural basins to managed watersheds for the purpose of providing water to urban centers has had a negative impact on semiarid ecosystems, worldwide. We view semiarid plant communities as being adapted to short, regular periods of drought. However, human induced changes in the water balance often remove these systems from the range of natural variability that has been historically established. This thesis explores vegetation changes over a 13-yr period for Owens Valley, in eastern California. Using remotely sensed measurements of vegetation cover, an extensive vegetation survey, field data and observations, precipitation records, and data on water table depth, I identify the key modes of response of xeric, phreatophytic, and exotic Great Basin plant communities. Three specific advancements were reached as a result of this work. (1) A change classification technique was developed that was used to separate regions of land-cover that were dependent on precipitation from regions dependent on groundwater. This technique utilized Spectral Mixture Analysis of annually acquired Landsat Thematic Mapper remote sensing data, to retrieve regional estimates of percent vegetation cover. (2) A threshold response related to depth-to-water dependence was identified for phreatophytic Alkali Meadow communities. Plant communities that were subject to groundwater depths below this threshold exhibited greater invasion by precipitation sensitive plants. (3) The floristic differences between previously cultivated and uncultivated land were found to account for an increased sensitivity of plant communities to precipitation variability. Through (2) and (3), two human influences (groundwater decline and previous land cultivation) were shown to alter land cover such that the land became more sensitive to precipitation change. Climate change predictions include a component of increased climate variability for the western United States; therefore, these results place serious doubt on the sustainability of human activities in this region. The results from this work broadly cover topics from remote sensing techniques to the ecology of Great Basin plant communities and are applicable wherever large regions of land are being managed in an era of changing environmental conditions.
机译：为了向城市中心供水，将大型自然流域转变为受管理的流域，对全世界半干旱生态系统产生了负面影响。我们认为半干旱植物群落已适应短期干旱。但是，人为引起的水平衡变化通常使这些系统脱离了历史上已经确定的自然变异范围。本文探讨了加利福尼亚东部欧文斯山谷在13年内的植被变化。通过使用遥感的植被覆盖度测量，广泛的植被调查，田间数据和观测，降水记录以及地下水位深度数据，我确定了干性，植物性和外来大盆地植物群落响应的关键模式。这项工作取得了三项具体进展。 （1）开发了一种变化分类技术，该技术用于将依赖降水的土地覆盖区域与依赖地下水的区域分开。该技术利用了每年获取的Landsat Thematic Mapper遥感数据的光谱混合分析，以获取植被覆盖率的区域估计。 （2）确定了水生碱草甸草甸群落的与水深相关性的阈值响应。受到低于该阈值的地下水深度的植物群落表现出更大的对降水敏感植物的入侵。 （3）发现以前耕种的土​​地和未耕种的土地之间的植物区系差异导致植物群落对降水变化的敏感性增加。通过（2）和（3），两个人为因素（地下水下降和以前的土地耕种）显示出改变了土地覆盖，使土地对降水变化变得更加敏感。气候变化预测包括美国西部气候变率增加的一个组成部分；因此，这些结果严重怀疑了该地区人类活动的可持续性。这项工作的结果广泛涵盖了从遥感技术到大盆地植物群落生态的主题，并且适用于在环境条件不断变化的时代管理大片土地的任何地方。

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