Changes in Spatiotemporal Patterns of 20th Century Spruce Budworm Outbreaks in Eastern Canadian Boreal Forests

Abstract

In scenarios of future climate change, there is a projectedincrease in the occurrence and severity of natural disturbances inboreal forests. Spruce budworm (Choristoneura fumiferana)(SBW) is the main defoliator of conifer trees in the North American boreal forests affecting large areas and causing marked losses of timber supplies. However, the impact and the spatiotemporal patterns of SBW dynamics at the landscape scale over the last century remain poorly known. This is particularly true for northern regions dominated by spruce species. The main goal of this study is to reconstruct SBW outbreaks during the 20th century at the landscape scale and to evaluate changes in the associated spatiotemporal patterns in terms of distribution area, frequency, and severity. We rely on a dendroecological approach from sites within the eastern Canadian boreal forest and draw from a large dataset of almost 4,000 trees across a study area of nearly 800,000 km2. Interpolation and analyses of hotspots determined reductions in tree growth related to insect outbreak periods and identified the spatiotemporal patterns of SBW activity over the last century. The use of an Ordinary Least Squares model including regional temperature and precipitation anomalies allows us to assess the impact of climate variables on growth reductions and to compensate for the lack of non-host trees in northern regions. We identified three insect outbreaks having different spatiotemporal patterns, duration, and severity. The first (1905–1930) affected up to 40% of the studied trees, initially synchronizing from local infestations and then migrating to northern stands. The second outbreak (1935–1965) was the longest and the least severe with only up to 30% of trees affected by SBW activity. The third event (1968–1988) was the shortest, yet it was also the most severe and extensive, affecting nearly up to 50% of trees and 70% of the study area. This most recent event was identified for the first time at the limit of the commercial forest illustrating a northward shift of the SBW distribution area during the 20th century. Overall, this research confirms that insect outbreaks are a complex and dynamic ecological phenomena, which makes the understanding of natural disturbance cycles at multiple scales a major priority especially in the context of future regional climate change.

Post-cutting Mortality Following Experimental Silvicultural Treatments in Unmanaged Boreal Forest Stands

“…Natural disturbance regimes determine the dynamics, structure and composition of forests and also control ecosystem functioning (Bergeron et al, 1999;Montoro Girona et al, 2018a;Portier et al, 2018). In forests characterized by long fire cycles, insect outbreaks and windthrow play important roles (Waldron et al, 2013;De Grandpré et al, 2018;Navarro et al, 2018). Windthrow can be difficult to predict (Klaus et al, 2011;Díaz-Yáñez et al, 2016) as it is a complex phenomenon influenced by multiple factors including climate, topography, forestry practices as well as stand and soil characteristics.…”

Dynamics of Territorial Occupation by North American Beavers in Canadian Boreal Forests: A Novel Dendroecological Approach

“…The main natural disturbances in the study area are spruce budworm (Choristoneura fumiferana Clem.) outbreaks [6], fire [5], and windthrow [7]. In this region, beaver density is around 0.01 to 0.27 colonies/km [44].…”

“…A dendroecological approach can be effective in reconstructing the impact of natural and anthropic disturbances in forest ecosystems [6,7,45]. To better understand how beaver colonies used the territory over time, we applied dendrochronological analysis to the shrub and tree species located around the lodges.…”

“…Natural disturbance regimes interact at multiple scales over time and determine the dynamics, structure, and composition of forests by altering ecosystem functioning, creating diversified habitats, and maintaining biodiversity [1][2][3][4]. The boreal forest is the second largest terrestrial biome in the world, and wildfires [5], insect outbreaks [6], and windthrow events are the main natural disturbances within these forests [7].…”

Aerial spraying of bacterial insecticides to control spruce budworm defoliation leads to reduced carbon losses

“…, Navarro et al. ). As the severity of future SBW outbreaks is predicted to increase, finding ways to mitigate forest damage will also contribute to reducing C emissions (Dymond et al.…”