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.

Spruce budworm (Choristoneura fumiferana (Clemens)) defoliation has been shown to increase the likelihood of large forest fires in central Canada. However, the time frame of heightened risk based on the duration of spruce budworm defoliation has not yet been quantified. In this article, we document the extent of stand breakdown and surface fuel accumulation after a period of spruce budworm defoliation that occurred between 1972 and 1976. Data on stand characteristics were derived from previous studies at three different locations in the boreal mixedwood forests of central Canada: Aubinadong (B.J. Stocks. 1987. For. Chron. 63: 8–14), Gogama, and Gowganda in Ontario. Stand breakdown was measured using a series of transects set in plots 7 years following aerially mapped defoliation (1977–1983). Results show that during the 4 years following 5 years of defoliation, crown breakage, a typical symptom of defoliation, increased by nearly 200%, and surface fuel increased by 145% from predisturbance levels. The high correlation between crown breakage and surface fuels linked defoliation to fuel buildup. We begin to solve the challenge of measuring fuel structure over the expansive scale of spruce budworm outbreaks by quantifying the relationship among stand breakdown, time since the end of defoliation, and the duration of defoliation so that the expected fuel structure can be modelled from annual defoliation surveys.

Climate change will have considerable impact on the global economy. Estimates of the economic damages due to climate change have focused on the effect of average temperature, but not the effect of other important climate variables. Related research has not explored the sub-annual economic cycles which may be impacted by climate volatility. To address these deficits, we propose a flexible, non-linear framework which includes a wide range of climate variables to estimate changes in GDP and project sub-annual economic cycle adjustments (period, amplitude, trough depth). We find that the inclusion of a more robust set of climate variables improves model performance by over 20%. Importantly, the improved model predicts an increase in GDP rather than a decrease when only temperature is considered. We also find that climate influences the sub-annual economics of all but one province in Canada. Highest stressed were the Prairie and Atlantic regions. Least stressed was the Southeastern region. Our study advances understanding of the nuances in the relationship between climate change and economic output in Canada. It also provides a method that can be applied to related economies globally to target adaptation and resilience management.