Doctoral Dissertation Research: Fire-Driven Alternative States and Spatial Variability in Forest Resilience at a Dry Forest Ecotone

这个博士论文项目将调查森林增益和损失的驱动因素，以及树木再生和再烧的严重程度，在一个地区，是高度敏感的环境变化-干燥的森林在东部山坡上的内华达州山脉的加州。通过研究自1950年以来干旱森林下缘的植被变化，以及这些系统自1986年以来如何应对火灾，博士生将研究森林和非森林的火灾驱动替代状态的潜力，以及地形和气候的精细尺度空间变异如何影响森林恢复力。鉴于已观察到和预测到的由于温度变化和干扰强度和频率增加而造成的干燥森林损失，确定干燥森林可能在何处和何时转变为另一种状态，对于制定保护森林覆盖的管理计划至关重要。该项目的结果将有助于指导管理处理，如规定的火灾，间伐和植树，通过确定有利于快速植被变化的景观和条件的部分。该项目还将通过本科生参与实地和实验室工作来加强科学培训和教育。干旱森林系统的未来变化很可能是突然的和非线性的，严重的干扰可能导致森林向非森林的转化，干扰和植被之间的正反馈在某种程度上使新的植被类型的镶嵌永久化。生态过渡带是生态系统之间的边界区域，处于变化动态的前沿。该项目将利用航空照片初步评估自1950年以来森林/草原交错带的森林、林地和草原分布情况如何变化，并将分布变化与地形、气候和扰动历史联系起来。接下来，将在1987年至2009年被烧毁的地区的同一地点调查一个野外地块网络，以评估火灾后树木再生及其驱动因素，以及火灾引起的替代植被状态的潜力。最后，将利用关于植被变化、火灾严重程度和干扰历史的遥感数据，评价自1984年以来在同一生态交错区被烧毁两次的地区的火灾-植被正反馈的潜力。通过该项目从内华达州东部的干燥森林动态中获得的见解将与美国和世界其他地方易受持续火灾驱动的植被变化影响的干燥森林生态交错区有关。

This doctoral dissertation project will investigate the drivers of forest gain and loss as well as tree regeneration and reburn severity in an area that is highly sensitive to environmental change - the dry forests on the eastern slopes of the Sierra Nevada Mountain of California. By examining vegetation change since 1950 at the lower margins of dry forest, and how these systems have changed in response to fires since 1986, the doctoral student will investigate the potential for fire-driven alternative states of forest and non-forest and how fine-scale spatial variability in topography and climate affect forest resilience. Given observed and predicted dry forest loss due to changes in temperature and increasing intensity and frequency of disturbances, determining where and when dry forests are likely to shift to an alternative state is critical to developing management plans to preserve forest cover. The results of this project will help guide management treatments such as prescribed fire, thinning and tree planting, by identifying portions of the landscape and conditions conducive to rapid vegetation change. This project will also enhance science training and education through participation of undergraduate students in field and laboratory work.Future change in dry forest systems is likely to be abrupt and nonlinear, with severe disturbance potentially causing a conversion of forest to non-forest and positive feedbacks between disturbance and vegetation to some extent perpetuating the new mosaic of vegetation types. Ecotones, the boundary regions between ecosystems, are at the leading edge of change dynamics. This project will use aerial photographs to initially assess how the distribution of forest, woodland and steppe have changed at a forest/steppe ecotone since 1950, and relate shifts in distribution to topography, climate and disturbance history. Next, a network of field plots will be surveyed at the same sites in areas burned between 1987 and 2009 to evaluate post-fire tree regeneration and its drivers and the potential for fire-originated alternative vegetation states. Finally, remote sensing data on vegetation change, fire severity and disturbance history will be used to evaluate the potential for positive fire-vegetation feedbacks in areas burned twice since 1984 at the same ecotone. Insights gained from dry forest dynamics in the eastern Sierra Nevada through this project will be relevant to dry forest ecotones that are vulnerable to persistent fire-driven vegetation change elsewhere in the U.S. and around the world.