Jack pine budworm (Choristoneura pinus pinus) populations undergo cycles of population irruption and collapse causing serious damage to jack pine (Pinus banksiana) forests. Outbreaks have been difficult to control and currently salvage logging in response to impending budworm damage is a major source of disturbance and land cover change in jack pine-dominated forests. Review of the twentieth-century history of jack pine budworm outbreaks in Wisconsin suggests that before European-American settlement (pre-settlement) jack pine budworm outbreaks could have either 1) occurred regularly, 2) outbreak activity could have varied in the past with changes in the structure and composition of jack pine-dominated forests, or 3) jack pine budworm outbreak activity could have increased substantially after settlement. Head capsule counts in sieved sedge peat sediment cores were used to reconstruct the changes in jack pine budworm outbreak activity over the last 1500 years in four forest hollow sites near Warner Lake, Wisconsin. General linear models of expected head capsule deposition, insect fossil degradation, pollen-inferred records of forest composition change, and the settlement horizon related the three pre-settlement outbreak activity scenarios to the fossil head capsule record. Likelihood of each model was used to sequentially update prior confidence in each hypothesis after the consideration of each fossil record.
Results/Conclusions
Collectively, the forest hollow histories from the sand plain in northwestern Wisconsin suggest increased jack pine budworm outbreak activity with European-American settlement. An array of hierarchically nested sampling plots in northwestern Wisconsin was monitored during a jack pine budworm outbreak to explore the changes in population processes that may have led to the historical change in jack pine budworm outbreak activity. Changes in the thresholds of population abundance at which density-dependent negative feedbacks to larval abundance are effective may account for the increased jack pine budworm outbreak activity in the twentieth century.
