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

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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.