Spruce Budworm (Choristoneura fumiferana Clem.) Defoliation Promotes Vertical Fuel Continuity in Ontario’s Boreal Mixedwood Forest

Graham Watt,Sandy Smith,Marie-Josée Fortin,Richard Fleming

doi:10.3390/f9050256

Graham Watt, Sandy Smith + Show 2 more

Open Access

https://doi.org/10.3390/f9050256

Copy DOI

Abstract

Spruce budworm, Choristoneura fumiferana (Clem.), defoliation has been shown to affect the occurrence of crown fire in Ontario, highlighting the need to better understand the driving factors of this effect on forest structure, including changes in fuel loading, type and position. Here, we investigate five boreal mixedwood sites within four zones that experienced different durations of continuous defoliation by spruce budworm in northeastern Ontario. Duration of defoliation had significant effects on vertical stand components, namely, host overstory to host understory crown overlap, host overstory and host understory crown to downed woody debris overlap, and downed woody debris height and quantity. Vertical stand components tended to increase with the duration of continuous defoliation, with the highest vertical fuel continuity occurring after 16 years of continuous defoliation. Such increases in the vertical spatial continuity of fuels may be a key reason for the greater percentage of area burned in those forests which have recently sustained a spruce budworm outbreak.

Highlights

The spruce budworm, Choristoneura fumiferana (Clem.), periodically erupts into large-scale outbreaks during which its favoured host species, balsam fir (Abies balsamea), and to a lesser extent white spruce (Picea glauca) and black spruce (Picea mariana), are defoliated and killed [1]
These data were collected in 1989, and showed the vegetation type to be boreal mixedwood composed of host and non-host (i.e., sugar maple (Acer saccharum), trembling aspen (Populus tremuloides), white cedar (Thuja occidentalis), white birch (Betula papyrifera) and yellow birch (Betula alleghaniensis)) trees
Vertical fuel continuity increased with the duration of defoliation

Summary

Introduction

The spruce budworm, Choristoneura fumiferana (Clem.), periodically erupts into large-scale outbreaks during which its favoured host species, balsam fir (Abies balsamea), and to a lesser extent white spruce (Picea glauca) and black spruce (Picea mariana), are defoliated and killed [1]. This insect is a major biotic disturbance throughout the boreal forest in the province of Ontario, Canada. During its last major outbreak (1977–1987), the spruce budworm defoliated roughly 20 million hectares in Ontario [1] and depleted an average of 35 million cubic meters of host tree wood volume annually in Canada [2]. Several years of defoliation can remove the majority of foliage from crown branches [5], initially causing growth reduction, but eventually leading to tree crown mortality termed

Methods

Results

Discussion

Conclusion