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Changes in Host Abundance Following Harvesting Desynchronize Forest Insect Pest Outbreaks

Photo of The Border Lakes Ecoregion contains (top) has starkly different land management histories separated by political boundaries. Divergent land management histories created differences in landscape patterns of spruce budworm host (i.e., spruce and fir) that were mapped using remote sensing. Spruce budworm disturbance histories reconstructed via tree-ring analyses across this study area include a range of outbreak frequencies and intensities (lower left, where position roughly corresponds to geographic location). The greatest variation in the time-series of outbreak patterns were explained by forest configuration, followed by forest proportion, and then the variance shared by these two variables, while climate accounted for comparatively little variation (lower left). USDA Forest ServiceThe Border Lakes Ecoregion contains (top) has starkly different land management histories separated by political boundaries. Divergent land management histories created differences in landscape patterns of spruce budworm host (i.e., spruce and fir) that were mapped using remote sensing. Spruce budworm disturbance histories reconstructed via tree-ring analyses across this study area include a range of outbreak frequencies and intensities (lower left, where position roughly corresponds to geographic location). The greatest variation in the time-series of outbreak patterns were explained by forest configuration, followed by forest proportion, and then the variance shared by these two variables, while climate accounted for comparatively little variation (lower left). USDA Forest ServiceSnapshot : A Forest Service scientist led an international team to investigate how different historic forest management practices have affected spruce budworm outbreaks in a large “experimental landscape” spanning the U.S.-Canadian border. Their results show the strongest evidence to date that human-mediated changes to forest landscapes affect the intensity and consequences of forest insect outbreaks at broad spatial scales.

Principal Investigators(s) :
Sturtevant, Brian R.  
Research Location : The US-Canadian border between Minnesota and Ontario.
Research Station : Northern Research Station (NRS)
Year : 2015
Highlight ID : 886

Summary

Humans shape landscape composition and structure with activities including fire suppression and timber harvests, leading to changes in fundamental ecosystem processes, but the extent to which they influence insect outbreak dynamics is unknown. A Forest Service scientist led an international team that studied 20th-century spruce budworm outbreak dynamics over a 6-million hectare (about 15 million acres) ecoregion straddling the border of Ontario,Canada, and Minnesota,USA. This ecoregion contains three contrasting forestland management legacies that have resulted in differences in forest composition and structure: fine-grained forest harvesting in Minnesota, coarse-grained forest harvesting in Ontario, and an unmanaged wilderness zone situated between the two with little recent harvest activity. The researchers reconstructed spruce budworm outbreak histories across management zones and climatic gradients using tree-ring chronologies at 16 locations. They found that forest composition and configuration explained 14 and 11 percent of the variance in outbreak variability, whereas climate explained only 0.2 percent. Results suggest that diverse forest landscapes will have lower probability of intense budworm outbreaks compared to landscapes dominated by host species, namely balsam fir and spruce. This study demonstrates the unintended impacts of human induced landscape-scale changes in forest structure on natural ecosystem functioning in general, and on insect outbreak dynamics in particular.

Forest Service Partners

External Partners

 
  • Barry Cooke, Canadian Forest Service, Edmonton, AB, Canada
  • Daniel Kneeshaw, University of Québec at Montreal, QC, Canada
  • Louis-Etienne Robert & Patrick M. A. James, University of Montreal, QC, Canada
  • Marie-Josée Fortin, University of Toronto, ON, Canada
  • Peter T. Wolter, Iowa State University, Ames, IA
  • Philip A. Townsend
  • University of Wisconsin, Madison

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