Dr. Emily Holt

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Spruce beetles (Dendroctonus rufipennis) parasitize Engelmann spruce trees (Picea engelmannii) which grow in subalpine forests between 9,000 and 11,500 feet (2,743 to 3,505 meters). These beetles are endemic to Colorado and traditionally contribute to forest renewal and succession; however, warming annual temperatures have increased beetle populations and stressed subalpine trees making the latter susceptible to a greater severity of infection. We predicted that spruce beetle disturbance would increase the available sunlight and nutrients to surrounding understory vegetation, slowly increasing understory species diversity of the area. To test this, we surveyed understory vascular plants from forty-four plots in subalpine forests using a chronosequence of over 20 years of spruce beetle infestation. We recorded 128 species across all age classes, the most common of which were Vaccinium scoparium (Kinnickinick), Abies bifolia (Subalpine fir), Picea engelmannii (Engelmann spruce), Arnica cordifolia (Heartleaf arnica), and Chamerion angustifolium (Fireweed). We also noted lower diversity in the recently affected plots and higher diversity in the plots affected over 14 years ago. Overall, our data suggest that vascular understory vegetation diversity increases slowly after spruce beetle infestation, however the presence of spruce saplings across the study area may indicate future spruce-fir forest regeneration in disturbed areas.

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