Doctoral Dissertation Research: Mountain Pine Beetle and Fire Influences on the Regeneration of Lodgepole Pine in Northern Colorado

自20世纪90年代末以来，严重的山松甲虫（MPB; Dendroctonus ponderosae）爆发和野火扰乱了科罗拉多州北部亚高山森林的大片地区。该地区MPB的主要寄主，黑松（Pinus contorta var. latifolia），被认为是一种典型的火适应物种，因为它有良好的球果习性（球果在热响应下打开），并且能够在林分替换后迅速建立起来。然而，在非火灾相关干扰（MPB流行病）下，晚熟球果和树苗招募如何响应，以及这种响应如何进一步影响未来火灾后的树木再生方面，存在实质性的知识缺口。在科罗拉多大学博尔德分校地理系Thomas Veblen教授的指导下，博士生Teresa Chapman研究了条件因素（如场地条件、林分结构、种子可用性和气候变化）如何决定黑松再生对最近MPB和火灾干扰的反应，以及MPB爆发后黑松再生的当前模式如何影响森林生态系统对未来火灾的反应。这些问题通过一系列四个目标在多个尺度上得到回答：1)比较2002年受严重火灾影响的地点和1996年以来受MPB流行影响的地点的黑松更新情况；2)通过实地试验调查不同凋落物深度和冠层条件下黑松的结尾松球果和发芽情况的反应；3)对科罗拉多州北部MPB后的地点进行大尺度采样，以生成再生模式和黑松群落的预测图。4)通过实施林分尺度树木更新预测模型和对当前MPB效应及其未来火灾预测后果的空间覆盖分析，综合经验生成的结果。该研究的基本假设是，在MPB大规模爆发后，目前的再生模式可能导致亚高山生态系统的火灾恢复能力下降。了解由于目前影响100多万公顷的MPB爆发而导致的长尾松死亡的生态后果，是落基山脉地区公众和土地管理者关注的一个主要问题。在严重的、罕见的干扰下，黑松自然更新动态的基本知识对于亚高山生态系统动态的短期和长期预测都是必不可少的。本研究产生的经验数据将为土地管理者提供初步基础，以评估由于MPB爆发与未来火灾的相互作用而导致森林组成变化的可能性。MPB流行病和2002年火灾的巨大范围和严重程度为研究这种可能对树种分布和区域尺度碳预算产生重要影响的大型，罕见的死亡事件的更新响应提供了罕见的自然实验。这项研究将为科罗拉多大学的众多本科生提供实地和实验室研究经验，并有机会撰写高级荣誉论文。

Since the late 1990s severe mountain pine beetle outbreak (MPB; Dendroctonus ponderosae) and wildland fires have disturbed large expanses of northern Colorado's subalpine forests. The primary MPB host in the region, lodgepole pine (Pinus contorta var. latifolia), is considered a classic fire-adapted species due to its serotinous cone habit (cones which open in response to heat) and ability to establish rapidly following stand replacing fires. However, there is a substantial knowledge gap in how serotinous cones and lodgepole seedling recruitment respond to non-fire related disturbances (MPB epidemics), and how this response may further influence tree regeneration following future fires. Doctoral student Teresa Chapman, under the supervision of Professor Thomas Veblen in the Department of Geography at the University of Colorado Boulder examines how conditioning factors (e.g. site conditions, stand structure, seed availability and climate variability) determine the response of lodgepole pine regeneration to recent disturbance by MPB and fire, and how the current patterns of lodgepole pine regeneration following MPB outbreak may affect forest ecosystem responses to future fire. These questions are answered through a series of four objectives at multiple scales: 1) to compare lodgepole pine regeneration at sites either affected by severe fire in 2002 or by the MPB epidemic since 1996, 2) to investigate through field experimentation the reaction of serotinous cones and lodgepole pine germination to variable litter depth and canopy conditions, 3) to conduct broad scale sampling of post-MPB sites across northern Colorado to generate predictive maps of both regeneration patterns and lodgepole serotiny, and 4) to synthesize the empirically generated results through both the implementation of a stand scale predictive model of tree regeneration and a spatial overlay analysis of current MPB effects and their predicted consequences following future fires. The underlying hypothesis of the research is that current patterns of regeneration following the extensive MPB outbreak could lead to less fire resilient subalpine ecosystems. Understanding the ecological consequences of lodgepole pine tree mortality due to the current MPB outbreak affecting over one million hectares is a major concern among the general public and land managers in the Rocky Mountain region. Basic knowledge of the natural regeneration dynamics of lodgepole pine following severe, infrequent disturbance is essential for both short- and long-term predictions of subalpine ecosystem dynamics. The empirical data generated by this research will provide land managers with an initial basis for evaluating the potential for shifts in forest composition due to the interactions of the MPB outbreak with future fires. The immense extent and severity of both the MPB epidemic and 2002 fires provide a rare, natural experiment to study the regeneration response to such large, infrequent mortality events which may have important impacts on tree species distributions and regional-scale carbon budgets. This research will provide numerous undergraduates at the University of Colorado with field and laboratory research experience and with opportunities to develop senior honors theses.