DISSERTATION RESEARCH: Temporal Dynamics of Alternative Stables States in a Desert Stream

了解生态系统对干扰的响应是生态学的核心问题，对于从局部到全球尺度的生态系统管理具有重要意义。两种主要的扰动理论是稳定性理论和多态理论，前者描述了生态系统在不同干扰条件下的收益率，后者描述了生态系统在不同的平衡条件(如草地和灌丛等)之间的转换。由于沙漠溪流经常受到洪水和干旱形式的严重干扰，这些生态系统为更广泛地了解生态系统对干扰的反应提供了极好的模型。在19世纪末之前，湿地(Cienegas)是美国西南部的一个共同特征，这些湿地的侵蚀使大多数干旱的溪流成为光秃秃的砾石河床(Arroyos)，代表了另一种平衡。最近在一个长期生态研究地点(亚利桑那州Sycamore Creek)观察到的湿地重建提供了一个机会，利用稳定性理论来评估沙漠溪流的交替配置如何对干扰做出反应。在洪水扰动后，我们将测量湿地和砾石床地的初级生产力和生态系统呼吸，以确定这两种不同的稳定状态对干扰的响应是否不同。这一建议的智力价值在于整合了生态系统对干扰的反应的单一和多重平衡理论。这项研究的更广泛的影响将是改善这个以前广泛存在的现在稀有的湿地生态系统的保护和恢复工作，并为研究生提供设计、执行和分析生态研究的培训机会。

Understanding the response of ecological systems to disturbance is a centralproblem in ecology, and is of fundamental importance to management ofecosystems from local to global scales. Two major theories of disturbanceare stability theory, which describes the rate of return of ecosystems topre-disturbance conditions, and multiple state theory, which describes thetransition of ecosystems between alternative equilibrium conditions (e.g.,grassland vs. shrubland, etc.). Because desert streams are subject tofrequent and severe disturbance in the form of both flood and drying, theseecosystems provide excellent models for understanding the response ofecosystems to disturbance more generally. Prior to the end of the 19thcentury, wetlands (cienegas) were a common feature of the Southwestern U.S.Erosion of these wetlands left most arid streams as bare, gravelbed channels(arroyos) that represent an alternative equilibrium. Recent observations ofwetland re-establishment at a long-term ecological study site (SycamoreCreek, AZ) provides an opportunity to evaluate how the alternativeconfigurations of desert streams respond to disturbances using the contextof stability theory. Following flash flood disturbance, we will measureprimary production and ecosystem respiration in both wetland and gravelbedsites to determine whether these alternative stable states differ in theirresponse to disturbance. The Intellectual Merit of this proposal lies inthis integration of single- and multiple-equilibrium theories of ecosystemresponse to disturbance. The Broader Impact of this research will be toimprove conservation and restoration efforts of this formerly-widespread andnow-rare wetland ecosystem, and to provide opportunities for training ofgraduate students in the design, execution, and analysis of ecologicalstudies.