Journal
FOREST ECOLOGY AND MANAGEMENT
Volume 289, Issue -, Pages 78-89Publisher
ELSEVIER
DOI: 10.1016/j.foreco.2012.10.004
Keywords
C/N ratio; Spruce beetle; Dendroctonus rufipennis; GLMM; Disturbance; Lake sediments
Categories
Funding
- Geological Society of America, Association of American Geographers
- National Science Foundation [1032099]
- Joint Fire Science Program [063131]
- Division Of Behavioral and Cognitive Sci
- Direct For Social, Behav & Economic Scie [1032099] Funding Source: National Science Foundation
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Recent outbreaks of native bark beetles are unprecedented during the historical period. The aim of this manuscript is to develop a proxy-based methodology to infer past bark beetle outbreaks using lake sediments to provide long-term context for recent outbreaks. We test three hypotheses to determine how the ecological impacts of severe spruce beetle (Dendroctonus rufipennis Kirby) disturbances are recorded in lake sediment deposits. The resulting mortality and defoliation of Engelmann spruce is hypothesized to: (1) decrease the ratio of spruce to fir pollen; (2) reduce canopy interception of precipitation leading to an increase in soil erosion and/or enhanced mobilization of terrestrial carbon; and (3) leach foliar nitrogen and enhance algal productivity resulting in increased nitrogen values in lake sediments. To test these hypotheses, we analyzed sediment cores from six spruce beetle-affected basins in Utah for spruce/fir pollen ratio (hypothesis 1), loss-on-ignition, magnetic susceptibility of sediments (hypothesis 2), and 8(13)C(BOM), 8(15)N(TN), elemental C and N, and the C/N ratio of bulk organic material (hypotheses 2 and 3). The dataset was statistically tested using general linear mixed models (GLMMs) to determine if the response variables differed significantly between outbreak and non-outbreak period. The spruce/fir pollen ratio responded significantly to outbreaks at all sites suggesting that this metric may be the most suitable for identifying past spruce beetle outbreaks. For our second hypothesis we found little support for an influx of terrestrial C due to strongly individualist responses of the basins. For our third hypotheses we found little support for increased sedimentary nitrogen, likely due to alterations to nutrient cycling from human activities. Therefore the host/non-host pollen ratio provides the most promising metric for detecting past outbreaks. (C) 2012 Elsevier B.V. All rights reserved.
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