NH023-0006
Simulation and analysis of the effect of spruce budworm on forest carbon dynamics: new TRIPLEX-Insect model development and applications

Friday, 11 December 2020
Poster
Zelin Liu, Hunan Normal University, Hunan, China, Changhui Peng, University of Quebec at Montreal, Institute of Environment Sciences, Montreal, QC, Canada and Daniel Kneeshaw, University of Quebec at Montreal, Centre for Forest Research, Montreal, QC, Canada
Abstract:
Spruce budworm (Choristoneura fumiferana (Clemens), Lepidoptera: Tortricidae, SBW) outbreaks play an important role in the boreal forests of North America. Carbon (C) dynamics in these forest ecosystems are severely affected by SBW outbreaks due to millions of square kilometers of forest loss from defoliation and mortality.

The overall aim of this research is to improve our quantitative understanding of the impact of insect disturbances on forest carbon dynamics. Especially, (1) a novel process-based model (TRIPLEX-Insect) was developed to quantify the effect of SBW outbreaks on forest carbon fluxes for balsam fir (Abies balsamea (L.) Mill.). (2) Using the TRIPLEX-Insect combined with forest inventory plots, geospatial databases, monthly climate data, and spatially explicit defoliation sequence data, we simulated carbon dynamics and changes between scenarios with and without SBW disturbances for 65,746 km2 of Québec. (3) The model has been further used to evaluate how much carbon would be saved by aerial spraying (i.e. a biological insecticide: Bacillus thuringiensis ssp. Kurstaki -- Btk) during 2010~2017 in Québec.

The model was validated against observed mortality in the North Shore region of Québec and published current annual volume increment (CAI) in the Cape Breton Island in Nova Scotia, Canada. Compared to simulations without defoliation, the average net ecosystem productivity (NEP) with defoliation decreased by 91±7.3 g C m-2year-1 in 65,746 km2 defoliated areas of Québec from 2007 to 2017. While there were 21,046 km2 of defoliated areas converted from C sink to source in 2017. This study also found that younger balsam fir stands lost less C than either spruce or mixed fir-spruce stands during the period of SBW outbreak 2007-2017 in Québec. Moreover, the aerial spraying was a good way to save C during the SBW attacks. In the year following spraying average NEP with spraying protection increased 0.59 g C m-2year-1 more than without spraying. The results also showed more C to be saved in balsam fir than either spruce or mixed fir+spruce forests in the year following spraying.

Overall, the TRIPLEX-Insect model is a useful tool for informing forest insect management initiatives. It can be applied to quantify the carbon dynamics as well as to evaluate the efficacy of aerial spray during spruce budworm outbreaks.

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