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一个对环境变化高度敏感的地区的森林收益和损失的驱动因素，以及树木再生和再燃烧的严重程度-加州内华达山脉东坡的干燥森林。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年以来如何响应火灾而发生变化，博士生将研究火灾驱动的森林和非森林替代状态的潜力，以及地形和气候的精细空间变异性如何影响森林的恢复力。鉴于观测到的和预测的干旱森林损失是由于温度变化和干扰强度和频率增加造成的，确定干旱森林可能在何时何地转变为另一种状态，对于制定保护森林覆盖的管理计划至关重要。该项目的结果将通过确定有利于植被快速变化的景观和条件，帮助指导管理处理，如规定的火灾、间伐和植树。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。未来干旱森林系统的变化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变，干扰和植被之间的正反馈在某种程度上使植被类型的新马赛克永续下去。过渡带是生态系统之间的边界区域，处于动态变化的前沿。该项目将使用航空照片来初步评估自1950年以来森林/草原过渡带的森林、林地和草原分布的变化，并将分布的变化与地形、气候和扰动历史联系起来。接下来，将在1987年至2009年期间被烧毁的地区的同一地点调查一个野外地块网络，以评估火灾后树木的再生及其驱动因素以及火灾引发的替代植被状态的潜力。最后，利用植被变化、火灾严重程度和扰动历史的遥感数据，对1984年以来同一交错带两次火灾的地区的火-植被正反馈潜力进行评价。通过该项目，从内华达山脉东部的干旱森林动态中获得的见解将与干旱森林过渡带相关，这些过渡带容易受到美国和世界其他地方持续火灾驱动的植被变化的影响。

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.