Disturbed Dendrochronology – Characterizing Changes in Tree Growth Due to Insect Outbreaks

Authors: Jodi Axelson*, University of California, Berkeley
Topics: Biogeography, Paleoenvironmental Change, Environmental Science
Keywords: forest entomology, forest change, dendrochronology, growth change detection
Session Type: Paper
Day: 4/6/2019
Start / End Time: 1:10 PM / 2:50 PM
Room: Marshall East, Marriott, Mezzanine Level
Presentation File: No File Uploaded

In western North America, disturbances impact thousands to millions of hectares of forests annually, and in many regions insects are the leading cause. Forest insects can be characterized by their feeding groups, each leaving their own signature on tree growth, mortality, and ecological patterns and processes. Two feeding groups – bark beetles in the genus Dendroctonus and defoliators in the genus Choristoneura have extensive ranges throughout North America and in many systems result in significant damage. Bark beetles, who are tree killers, result in large pulses of mortality in their host trees when they experience outbreaks. Thus, outbreaks are a stand releasing disturbance at small spatial scales, and at large spatial scales can reorient successional trajectories across the landscape. Defoliators, on-the-other hand, rarely result in the death of their host, and instead outbreaks result in stand-to-landscape scale suppression signals in the tree-ring record. Here I summarize the stand-level impacts of the mountain pine beetle (Dendroctonus ponderosae) on lodgepole (Pinus contorta) in mountain ecosystems; and regional to landscape level impacts of western spruce budworm (Choristoneura freemani) on Douglas-fir (Pseudotsuga menziesii) across significant portions of its range. I will explore the approaches to characterizing changes in tree growth from these two different feeding groups, and explore the challenges in understanding the relative contribution of insect outbreaks and climatic variability on tree-growth patterns.

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