A tree-ring reconstruction of western spruce budworm history in the southern Rocky Mountains

Abstract

Tree-ring width chronologiesfr om ten mixed-conifers tandsi n the Colorado Front Range and New Mexico Sangre de Cristo Mountains were used to reconstruct the timing, duration, and radial growth impacts of past outbreaks of western spruce budworm (Choristoneura occidentalis Freeman). At least nine outbreaks were identified in the stands from 1700 to 1983. Severity and timing of outbreaks was highly variable. The average duration of reduced growth periods caused by budworms was 12.9 years and ranged from 5 to 26 years. The average interval between initial years of successive outbreaks was 34.9 years and ranged from 14 to 58 years. The average maximum and periodic radial growth reductions were 50% and 21.7%, respectively. There was a relatively long period of reduced budworm activity in the first few decades of the twentieth century, and since that time outbreaks have been markedly more synchronous among the sampleds tands.I t is hypothesizedth at the increaseds ynchroneityo f outbreaks in the latter half of the twentieth century is due to changes in age structure and species composition following harvesting and fire suppression in the late nineteenth and early twentieth centuries.

Citation

Swetnam, Thomas W.; Lynch, Ann M. 1989. A tree-ring reconstruction of western spruce budworm history in the southern Rocky Mountains. Forest Science. 35(4): 962-986.