Doctoral Dissertation Research: Spatio-Temporal Variability of Ponderosa Pine Susceptibility to Mountain Pine Beetle in the Colorado Front Range

树皮甲虫种群的周期性爆发会导致广泛的树木死亡，这会影响林分结构，并可能创造持久的生态遗产。目前(1995年后)在科罗拉多州北部黄松林中爆发的山松甲虫(Dendroctonus Ponderosae)在空间上是不同的，似乎受到许多因素的影响，这些因素影响着一系列空间和时间尺度。研究人员不完全了解MPB引起的黄松死亡的生物和非生物制约因素，以及随着疫情在时间和空间上的进展，这些制约因素是如何变化的。这项博士论文研究项目将阐述生物(树木和植被属性)和非生物(地形)因素如何在树木、林分和景观尺度上影响科罗拉多前缘山脉东坡山地地带黄松树最近MPB活动的传播。它将研究以前的火灾如何影响受复杂干扰历史影响的不同群落类型和植被结构的异质景观中黄松林MPB活动的发生概率和严重程度。这位博士生将收集20个地点的现场数据，这些数据嵌套在以前的火灾历史样本区域(树木年轮和火痕数据)，他将分析这些数据和其他数据，以阐明在树木尺度(例如树木直径)和林分尺度(例如相邻间伐、火灾历史)下生物和非生物因素对黄皮松MPB易感性的时空影响。高分辨率卫星图像将被用来分析MPB引起的树木死亡的景观尺度时空模式。学生将使用逻辑回归或证据权重，在科罗拉多州中部和北部前线地区当前疫情的早期(2002)和更高阶段(2008)产生MPB感染的预测模型。他假设，随着疫情的进展，树木和林分水平对黄皮松对MPB的易感性的限制将变得不那么重要。另一个有待探索的假设关系是，自上次大火以来增加的时间将增加黄皮松对MPB侵袭的敏感性，因为先前的研究已经确定了树木密度和大小以及自上次大火以来的时间是黄皮松对MPB侵染的易感性的决定因素。该项目的多尺度研究方法将分析MPB侵染的生物和非生物驱动因素的复杂时空变化，它将提供关于先前火灾对MPB风险的影响的新信息和见解，增强我们对科罗拉多州森林中干扰相互作用的了解。了解这种非线性、跨尺度的相互作用对于预测气候变化条件下森林的时空动态至关重要。在科罗拉多州的前线地区，郊外向荒地城市交界处的发展日益增加，突显了了解农村社区周围地区森林动态的重要性。目前，MPB引起的树木死亡及其对火灾的潜在影响引起了公众的极大关注。这项计划将告知土地管理人员和业主有关MPB侵扰的高风险地区，并将有助于最大限度地发挥消防和MPB管理政策的有效性。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。

Periodic eruptions of bark beetle populations cause widespread tree mortality, which affects stand structure and can create a lasting ecological legacy. The current (post-1995) mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak in ponderosa pine (Pinus ponderosa) forests of northern Colorado is spatially heterogeneous and appears to be influenced by numerous factors operating across a range of spatial and temporal scales. Researchers do not fully understand biotic and abiotic constraints of MPB-caused mortality in ponderosa pine as well as how those constraints change as an outbreak advances over time and space. This doctoral dissertation research project will address how biotic (tree and vegetation attributes) and abiotic (terrain) factors have affected the spread of recent MPB activity in ponderosa pine in the montane zone of the eastern slope of the Colorado Front Range at the tree, stand, and landscape scales. It will examine how previous fires affect the probability of occurrence and severity of MPB activity in ponderosa pine stands in a heterogeneous landscape of different community types and vegetation structures affected by a complex disturbance history. The doctoral student will collect field data from 20 sites nested within areas previously sampled for fire history (tree-ring and fire-scar data), and he will analyze these and other data to elucidate spatio-temporal influences of biotic and abiotic factors affecting ponderosa pine susceptibility to MPB at the tree scale (e.g. tree diameter) and stand scale (e.g. adjacent thinning, fire history). High-resolution satellite imagery will be used to analyze landscape-scale spatio-temporal patterns of MPB-caused tree mortality. The student will use logistic regression or weights of evidence to produce predictive models of MPB infestation at an early (2002) and a more advanced (2008) stage of the current outbreak for the central and northern Colorado Front Range. He hypothesizes that as an outbreak advances, the tree and stand-level constraints on susceptibility of ponderosa pine to MPB will become less important. Another hypothetical relationship to be explored is that that increased time since the last severe fire will elevate the susceptibility of ponderosa pine to MPB attack, because previous studies have identified tree density and size as well as the time since the last severe fire as determinants of ponderosa pine susceptibility to MPB infestation.This project's multi-scale research approach will analyze the complex temporal and spatial variation of biotic and abiotic drivers of MPB infestation, and it will provide new information and insights regarding the effects of previous fires on MPB risk enhancing our knowledge of disturbance interactions in Colorado's forests. Understanding such non-linear, cross-scale interactions is essential to predict the spatio-temporal dynamics of forests under changing climate conditions. In Colorado's Front Range, increased exurban development into the wildland urban interface has highlighted the importance of understanding forest dynamics in areas surrounding rural communities. There currently is great public concern over MPB-caused tree mortality and its potential effects on fire hazard. This project will inform land managers and owners about areas of high risk to MPB infestation and will aid in maximizing the effectiveness of fire and MPB management policies. 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.