Doctoral Dissertation Research: The Effects of Climate and Disturbance Variation on Post-Fire Regeneration of Madrean Pine-Oak Forests in Mexico's Sierra Madre Occidental

人类活动引起的全球气候变化的生态效应对于理解和预测气候驱动的植被变化日益受到关注。现有的全球环流模型可以预测未来的气候和粗尺度植被模式的变化。然而，这些模型的有效性受到时间和空间尺度问题的限制，以及对气候变化和人类土地利用变化如何影响干扰制度和随后的植被格局的理解不足。这一博士论文研究项目将有助于理解每年到十年尺度的气候变化如何与人类对墨西哥中北部景观的影响相互作用，从而影响火灾后马德里安松树生态系统的更新成功和物种分布。具体目标是：1)评估气候变化和人类土地利用方式的变化如何影响马德里安松树生态系统的火情；2)气候变化和火情的变化如何相互作用调节苗木的建立和成功；3)测试在北美其他地区确定的生态系统/群落对气候和土地利用的反应是一般的生态反应，还是取决于特定类群的生活史特征。标准的树木年轮研究技术将被用来得出树木的形成日期、树龄频率，并在一组研究地点重建过去的火灾状况，这些地点在气候变化明显的背景下反复受到人类的干扰。相关分析和回归分析技术的结合将被用来确定不同空间和时间尺度上的建树时间模式。这项研究的结果将被用来检验普遍的假设，即马德兰松树生态系统的苗木建立与气候变化和火情变化有关。据预测，在大范围、生物上严重的火灾之后，苗木的建立将发生在多年到十年降雨量高于平均水平的时期。据预测，大范围的火灾年将发生在降雨量低于平均水平、气温高于平均水平的年度至多年期间。据预测，人类将通过改变燃料的数量和连续性以及作为引火源来影响火灾的发生和严重程度。最终，在墨西哥中北部确定的特定地点的生态系统/群落对气候和土地利用变化的反应将与其他地区之前的研究结果进行比较，以测试这些反应是一般的生态反应，还是依赖于特定类群的生活史特征。研究气候变化和人类土地利用如何影响火场和随后的植被格局，对于预测全球变化的生态影响具有重要意义。这项研究将提供关于气候和人类与火灾制度的相互作用如何影响墨西哥中北部火灾后苗木建立的成功的基本信息。这项研究具有广泛的生态学意义，因为它将检验北美其他地区在不同降水和温度趋势下分类不同的生态系统对火灾、树木建立和树木死亡的气候影响假说。这项研究还将提供更多的信息，以澄清气候和人类影响对植被变化的作用，这是由于气候差异，以及整个北美人类迁徙的时间和随后的土地利用做法的差异。此外，我们在墨西哥和北美其他地区的生态系统特征的差异将使我们能够测试先前研究中确定的生态系统对气候和土地利用变化的反应是一般的生态反应，还是取决于特定类群的生活史特征。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。

The ecological effects of anthropogenic global climate change are of increasing concern for understanding and predicting climate driven vegetation change. Global circulation models exist that predict future climates and changes in coarse scale vegetation patterns. However, the efficacy of these models is limited by temporal and spatial scale problems and a poor understanding of how climate variation and human land use changes influence disturbance regimes and subsequent vegetation patterns. This doctoral dissertation research project will help to understand how annual to decadal scale climatic variation interacts with human influences on the landscape in north-central Mexico to effect changes in the fire regime and subsequently affect the regeneration success and species distributions of Madrean pine-oak ecosystems after fire. The specific objectives are: 1) to assess how climate variation and changes in human land use practices influence the fire regime in Madrean pine-oak ecosystems, 2) how climate variation and alterations to the fire regime interact to regulate seedling establishment and success, and 3) to test if ecosystem/community responses to climate and land use identified in other regions of North America are general ecological responses or are dependent on the life history traits of specific taxa. Standard tree-ring study techniques will be used to derive tree establishment dates, tree age frequencies, and reconstruct past fire regimes in a set of study sites that have been repeatedly disturbed by humans within a context of pronounced climatic variability. A combination of correlation analysis and regression analysis techniques will be used to identify temporal patterns of tree establishment at different spatial and temporal scales. The results of this study will be used to test the general hypothesis that seedling establishment in Madrean pine-oak ecosystems is related to climate variation and variations in the fire regime. Seedling establishment is predicted to occur during multi-annual to decadal periods of above average precipitation that follow widespread, biologically severe fires. Widespread fire years are predicted to occur during annual to multi-annual periods of below-average precipitation and above-average temperature. Humans are predicted to influence the occurrence and severity of fires by altering fuel quantity and continuity and serving as ignition sources. Ultimately, the site specific ecosystem/community responses to climate and land use variation identified in north-central Mexico will be compared with previous results from studies in other regions to test if these are general ecological responses, or if they are dependent on the life history traits of specific taxa. The study of how climate variation and human land use affect the fire regime and subsequent vegetation patterns has important consequences for predicting the ecological effects of global change. This study will provide basic information concerning how climate and human interactions with the fire regime affect the success of seedling establishment after fires in north-central Mexico. This research has broad ecological significance in that it will test previous hypotheses of climatic influences on fire, tree establishment, and tree mortality that were developed in other regions of North America with taxonomically different ecosystems under different precipitation and temperature trends. This study will also provide additional information to clarify the roles of climatic and human influences on vegetation change due to the climatic differences, and the differences in the timing of human migrations and subsequent land use practices throughout North America. Moreover, the differences in ecosystem characteristics between our sites in Mexico and other areas of North America will allow us to test whether the ecosystem responses to climate and land use changes identified in previous studies are general ecological responses or are if they dependent on the life history traits of specific taxa. 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.