Doctoral Dissertation Research: Spatial and Temporal Dynamics of Salt Marsh Vegetation across Scales

盐沼具有植被和环境因子的多尺度时空动态特征，这意味着必须了解尺度和变化之间的相互关系。认识到很少有研究明确阐述不同尺度上的这种动态，这项博士论文研究旨在填补丹麦斯卡林根盐沼的知识空白。首先，与主要强调海平面长期、逐渐上升的影响相比，关于海洋表面暴风雨引发的短期风潮如何影响植物物种组成的信息很少。其次，虽然对包括内外沼泽在内的大范围生物和非生物模式进行了大量研究，但对潮汐小溪上土壤和地形梯度的植被精细分区的关注较少。第三，还没有认识到不同物种组成或演替阶段应该有不同的沉积速率。第一个空白将根据自20世纪30年代初S以来获得的植物种类发生和沼泽泛滥频率的数据来填补。初步分析证明，泛滥频率与海洋风暴密切相关。这种相关性将有助于理解植被演替对短期风潮的响应。第二个问题将通过比较微尺度的物种区划和潮汐小溪被淹没的海水的排放来解决。例如，在前期野外工作中观察到的岩滩边缘晚演替物种的优势可以用高堆积密度和粗糙的底质来解释。这样的土壤物理条件表明有足够的咸水排水。第三个问题将通过对四个不同地点的沉积物岩心进行测年来回答，每个地点都有不同的演替阶段(即早期、早期到中期、中期到晚期和晚期)。每个岩心将被切成1厘米厚的切片，并采用恒定初始浓度的伽马能谱方法测定年龄。这些程序将显示不同物种组成的每个地点每年发生的沉淀量。这项研究的意义在于科学和社会两个角度。在科学考量方面，本研究将实现盐沼生态在时间和空间尺度上的整合。在时间上，海平面的长期和短期变化都可能解释植被动态，挑战长期变化是主要驱动力的传统信念。在空间上，认识到跨越潮汐小溪的微尺度过程的重要性，这项研究将强调采取分级战略的必要性，同时考虑到广泛和精细尺度的生态。此外，第三个目标的实现将通过引入测年方法来量化植被-沉积关系，从而导致方法上的进步。在社会意义上，这项研究为主要关心长期、逐渐的海平面变化的海岸带管理者和政策制定者提供了关于短期风潮重要性的新见解。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Salt marshes are characterized by multi-scale spatial and temporal dynamics of vegetation and environmental factors, which means that both scale and change must be understood relative to each other. Recognizing that few studies have explicitly addressed such dynamics at various scales, this doctoral dissertation research aims to fill knowledge gaps on the Skallingen salt marsh in Denmark. First, compared to the major emphasis on the effect of long-term, gradual sea-level rise, there is little information about how short-term wind tides driven by storminess on the ocean surface influence changes in plant species composition. Second, while much research was conducted on broad-scale biotic and abiotic patterns encompassing outer and inner marshes, fine-scale zonation of vegetation in response to edaphic and topographic gradients across tidal creeks has received less attention. Third, it has not been recognized that there should be different rates of sedimentation depending on species composition, or successional phase. The first gap will be filled based on data on plant species ocurrence and over-marsh flooding frequency acquired since the early 1930's. Preliminary analysis proved that the inundation frequency is closely related to the ocean storminess. Such a correlation will facilitate the understanding of vegetation succession in response to short-term wind tides. The second problem will be solved by comparing micro-scale species zonation and the drainage of inundated sea water across tidal creeks. For example, the dominance of late-successional species on cutbank edges observed during preliminary field work will be explained by high bulk density and coarse-textured substrate. Such soil physical conditions are indicative of adequate drainage of saline water. The third question will be answered by dating sediment cores from four different sites, each characterized by different successional stages (i.e. early, early to mid, mid to late, and late). Each core will be sliced into 1 cm-thick sections and dated by means of gamma spectrometry using the constant initial concentration method. These procedures will show how much sedimentation has occurred annually at each site with different species composition. The significance of this research lies in both scientific and societal perspectives. In terms of the scientific consideration, the study will achieve the integration of salt marsh ecology across temporal and spatial scales. Temporally, both long-term and short-term sea-level variations will likely explain vegetation dynamics, challenging the conventional belief that the long-term variation is the primary driver. Spatially, recognizing the significance of micro-scale processes across tidal creeks, this research will emphasize the need for adopting hierarchical strategies that take both broad- and fine-scale ecology into consideration. In addition, accomplishment of the third objective will result in a methodological advancement by introducing dating methods to quantifying vegetation-sedimentation relationships. In a societal sense, this research delivers new insights on the importance of short-term wind tides to coastal zone managers and policy makers who have primarily been concerned with long-term, gradual sea-level changes. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.