Effects of forest management legacies on spruce budworm (Choristoneura fumiferana) outbreaks

Abstract

The “silvicultural hypothesis” of spruce budworm ( Choristoneura fumiferana Clem.) dynamics postulates that increasing severity of spruce budworm outbreaks over the last century resulted from forest conditions created by past management activities. Yet, definitive tests of the hypothesis remain elusive. We examined spruce budworm outbreak dynamics (synchrony, periodicity, and intensity) in the 20th century using historical reconstruction from tree-ring chronologies sampled within 19 sites in a large ecoregion located on the border of Minnesota and Ontario. The study encompassed three areas affected by contrasting management legacies: a fine-grained area (Minnesota, six sites, average cut size = 17 ha), a coarse-grained area (Ontario, six sites, average cut size 10 times that of Minnesota), and a conservation zone (seven sites) with little recent harvest activity overlapping the border. Results suggest important differences in outbreak dynamics between the forest management zones that cannot be explained by differences in climate among sample sites. Budworm outbreaks within the conservation zone were more synchronous, with more trees per site affected and less frequent outbreaks than sites sampled within fine-scale managed areas. Outbreak dynamics within forests managed at coarser scales suggest a mixture of the conservation and fine-scale management zone outbreak patterns. Potential factors affecting differences in the observed outbreak patterns include forest pattern, composition, and age. Our study generally supports the silvicultural hypothesis and emphasizes that management legacy effects on spruce budworm dynamics should be observable at landscape scales, as well as at local scales.

Analysis of combined data sets yields trend estimates for vulnerable spruce-fir birds in northern United States

“…Future studies that compare trends from the present study with those in more northerly Canadian populations may be able to determine whether climate change is directly contributing to trends in avian abundance. Similarly, the severity and periodicity of spruce budworm (Choristoneura fumiferana) outbreaks differs considerably between the Midwestern and Eastern regions (Fraver et al, 2007;Robert et al, 2012), providing an opportunity to determine how this disturbance agent might be impacting long-term trends in associated bird species. Further investigations to identify point-level environmental and disturbance factors driving trends and how climate change affects those factors are currently under way.…”

Forest recovery patterns in response to divergent disturbance regimes in the Border Lakes region of Minnesota (USA) and Ontario (Canada)

“…For example, forest type bias was not evident in 2000 when wilderness disturbance was dominated by a relatively indiscriminant blow down disturbance event (Frelich, 2002). By contrast, disturbances were biased toward conifer types in 1990 and 1995, corresponding with a peak in budworm defoliation (Robert et al, 2012) and large wildfires (Fig. 3), respectively.…”

“…Yet there is also increasing recognition that more persistent early successional stages and greater range of variability in recovery time observed following many natural disturbances can play an important role in the regional biodiversity of predominantly forested areas (Swanson et al, 2011). In addition, Robert et al (2012) found the legacy of land management in this region influences spatiotemporal dynamics of insect outbreaks, suggesting repercussions for sustainable forestry and regional forest health. Our approach can therefore help inform land managers who must balance a diversity of objectives and values over time and space.…”

“…In many systems forest recovery can be delayed due to either poor tree recruitment (Foster, 1983;Simard, 2009), competition with established understory vegetation (Royo and Carson, 2006;Gilliam, 2007), or both (Lavoie and Sirois, 1998). Such delays have longterm consequences for landscape age structure, with implications for sustainable forestry (Doyon et al, 2011), carbon storage (Pan et al, 2011), insect outbreaks (Robert et al, 2012), and wildlife habitat (Manolis et al, 2002;King et al, 2009;Landriault et al, 2012).…”

Estimating forest vulnerability to the next spruce budworm outbreak: will past silvicultural efforts pay dividends?

“…Volume 398 reduction was least under the increased spruce objective, assuming black spruce, at 20% by the 399 end of the outbreak simulation (Fig. However, our 434 results may not entirely address this question, as host connectivity or forest contiguity, which 435 were not accounted for in our model, could play a role in determining the damage generated by 436 SBW at the landscape scale (Robert et al 2012). 9b).In comparison, volume reductions for unmanaged stands, increased mixedwood and 401 balanced composition objectives were 43-44% assuming that spruce was black, versus 50-53% 402 assuming that spruce was white.…”