Development of a New TRIPLEX-Insect Model for Simulating the Effect of Spruce Budworm on Forest Carbon Dynamics

Zelin Liu,Changhui Peng,Jean-Noël Candau,Louis De Grandpré,Daniel Kneeshaw,Xiaolu Zhou

doi:10.3390/f9090513

Abstract

The spruce budworm (SBW) defoliates and kills conifer trees, consequently affecting carbon (C) exchanges between the land and atmosphere. Here, we developed a new TRIPLEX-Insect sub-model to quantify the impacts of insect outbreaks on forest C fluxes. We modeled annual defoliation (AD), cumulative defoliation (CD), and tree mortality. The model was validated against observed and published data at the stand level in the North Shore region of Québec and Cape Breton Island in Nova Scotia, Canada. The results suggest that TRIPLEX-Insect performs very well in capturing tree mortality following SBW outbreaks and slightly underestimates current annual volume increment (CAI). In both mature and immature forests, the simulation model suggests a larger reduction in gross primary productivity (GPP) than in autotrophic respiration (Ra) at the same defoliation level when tree mortality was low. After an SBW outbreak, the growth release of surviving trees contributes to the recovery of annual net ecosystem productivity (NEP) based on forest age if mortality is not excessive. Overall, the TRIPLEX-Insect model is capable of simulating C dynamics of balsam fir following SBW disturbances and can be used as an efficient tool in forest insect management.

Highlights

Spruce budworm (Choristoneura fumiferana (Clemens), Lepidoptera: Tortricidae) (SBW) outbreaks play a key role in the dynamics of eastern North America’s boreal and temperate forest biome [1,2,3,4].In recent centuries, spruce budworm (SBW) outbreaks have occurred cyclically every 30–40 years in eastern NorthAmerica [5] with a new outbreak beginning in 2006 [6]
We successfully developed the TRIPLEX-insect model, which is a new process-based sub-model that takes into account annual defoliation (AD), cumulative defoliation (CD), and tree mortality inputs to ascertain C
This study found that the capacity of

Summary

Introduction

Spruce budworm (Choristoneura fumiferana (Clemens), Lepidoptera: Tortricidae) (SBW) outbreaks play a key role in the dynamics of eastern North America’s boreal and temperate forest biome [1,2,3,4].In recent centuries, SBW outbreaks have occurred cyclically every 30–40 years in eastern NorthAmerica [5] with a new outbreak beginning in 2006 [6]. Spruce budworm (Choristoneura fumiferana (Clemens), Lepidoptera: Tortricidae) (SBW) outbreaks play a key role in the dynamics of eastern North America’s boreal and temperate forest biome [1,2,3,4]. SBW outbreaks have occurred cyclically every 30–40 years in eastern North. Balsam fir (Abies balsamea (L.) Mill.), an important conifer in Canada’s boreal forest, is the tree species most vulnerable to SBW [4,7,8,9]. A modification of carbon (C) exchanges occurs in balsam fir forests during outbreaks as the defoliator destroys photosynthetic tissues, resulting in a reduction of tree growth and an increase in mortality [10,11,12]. SBW mainly consumes foliage produced in the current year. Given that needles typically remain on the tree for five to six years, it can take many years for the SBW to kill a Forests 2018, 9, 513; doi:10.3390/f9090513 www.mdpi.com/journal/forests

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