Decomposition and carbon loss in lodgepole pine (Pinus contorta var. latifolia) wood following attack by mountain pine beetle (Dendroctonus ponderosae)

Abstract

Mountain pine beetle (MPB)-killed wood remaining on the landscape is predicted to release significant amounts of carbon to the atmosphere as it decays. A lack of field-based wood decomposition data for validating simulation models reduces certainty in such predictions.Using a chronosequence approach, I quantified decomposition of MPB-killed wood to improve decay rate parameters. Changes in carbon density over time and climatic variability showed distinct patterns for bole position categories. Snag carbon density was similar to that of live lodgepole pine, and did not change considerably with time or climatic influences.Decay in suspended boles increased with summer precipitation, but declined with increasing summer temperature, suggesting decay in elevated boles is moisture-limited on warmer sites. Down boles decayed four times faster with increasing proximity to the soil than suspended boles, but did not clearly reflect climatic influences. Position of dead boles appears more important for wood decay than previously thought.

Selected Examples of Interactions Between Natural Disturbances

“…Furthermore, in accelerating post-beetle tree collapse, wind contributes to the accumulation of boles resting on the ground and having contact with the forest floor. This accumulation further accelerates fungal attack and decomposition and elevates the rate of CO 2 release due to tree decay (Kaytor, 2016). Although inadequately documented, greater concentrations of fallen beetle-killed trees could plausibly result in more intense wildfires (Jenkins et al, 2012), especially if fallen trees are jack-strawed, i.e., collapsed at multiple intersecting angles with many boles elevated above the ground and staying well dried, leading to a three-way interaction between insects, wind, and fire.…”

Long-term effects of timber harvesting on coarse woody debris dynamics and marten habitat

“…Harvesting equipment contributes to the mechanical reduction of logging debris and legacy CWD, which often results in the CWD being less elevated above the ground and more fragmented (McCarthy and Bailey 1994). CWD decay rates and losses may be altered by harvest dependent micro-site climate shifts, changes in substrate quality (Harmon et al 1986), and the relative elevation of CWD pieces from the ground (Kaytor 2016). Harvest operations will also shift future CWD addition rates by altering both the abundance and condition of the remaining trees (Densmore et al 2004).…”

“…Longer pieces (>2 m) are used as runways and refuges by marten in the winter (Bunnell and Houde 2010) and they are more likely to be stacked, supporting preferred structural complexity (Bull and Heater 2000). Pieces elevated off the ground decay slower (Kaytor 2016), retaining wood strength and provide greater structural complexity which in turn creates subnivean access points (Mclaren et al 2013). These CWD characteristics can be incorporated together to form a CWD habitat suitability index that can be evaluated at a plot, and potentially landscape level, to assess the habitat value of CWD for marten and other CWDdependent mammals such as, fishers, mice, and voles (Farnell et al 2020).…”