How Will Forests Change Due to Spruce Beetle?

The effects of a large-scale spruce beetle outbreak are likely to be visible and evolving on the landscape for many years.

NPS Illustration / M. Perez

Spruce beetles have lived in the Denali area for a long time, causing death of individual and patches of spruce trees now and again. However, with large numbers of beetles causing many trees to die in just a few years, one may be concerned about the health of the forest.

PAST (Spruce beetle at endemic population levels): Spruce beetles have been present in Denali as long as spruce has been a dominant part of the vegetation. Spruce beetle population has likely varied over time and across space, with small-scale outbreaks causing some trees to die each year. Research in dendrochronology (the study of tree rings) indicates that regional beetle outbreaks have occurred several times in the last 200 hundred years in south-central Alaska (Berg et al. 2006), but the history of large-scale beetle outbreak in the Denali area is not as clear. Slower-growing trees and more frequent fire limit the availability of a detailed tree ring record to study.

PRESENT (Spruce beetle at outbreak population levels): The visual effects of the current spruce beetle infestation are alarming. In some areas of the outbreak, it appears there are more dead trees than live ones, and the trees attacked by spruce beetle have died very quickly. An ongoing study conducted by the park’s botany team at sites located within a few miles of the Denali Park Visitor Center indicated that in 2023, 3% of ~2000 trees visited were infested with spruce beetle, while by 2024, 11% of trees were infested. Looking more at the forest than the trees revealed that of 37 sites visited, 50% of the sites contained infested trees in 2023, increasing to 76% of sites infested in 2024 (Roland et al. 2024, unpublished data). These numbers show the outbreak is well underway in the Denali area and additional mortality of spruce is expected.

FUTURE (Spruce beetle returns to endemic population levels): Nature can seem static when it’s a part of our daily lives, but nature is ever-changing and not constrained by human timelines. Spruce beetle is one of many natural disturbances a forest may face. As the current beetle outbreak continues, the green forest we have grown accustomed to may lose its familiarity. Much of the densely forested area near the Denali National Park and Preserve entrance and along the Denali Park Road is likely to experience moderate to high rates of spruce mortality.

However, spruce is just one part of the forest. Forests to the north are more spatially patchy, contain more black spruce, and generally grow slower than those in the south. It may become more difficult for spruce beetles to locate and infest suitable host trees. Additionally, beetles may struggle to keep their population high with more frequent extreme cold temperatures (e.g., 40 below zero). To understand nature, is to be observant and accept all outcomes.

 

Information here was summarized from:

Roland, C., Walton, J., and Tomerlin, M. (2024). Spruce beetle monitoring project, data exploration. Preliminary results from in-progress research supported by the NPS Inventory and Monitoring Program, Central Alaska Network, and Denali National Park and Preserve.

Berg, E. E., Henry, J.D., Fastie, C.L., De Vodler, A.D., and S.M. Matsuoka. 2006. Spruce beetle outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to summer temperatures and regional differences in disturbance regimes. Forest Ecology and Management 227(3): 219-232.

Matsuoka, S., Holsten, E. H., Shephard, M. E., Werner, R. A., and R. E. Burnside (eds). 2006. Spruce beetles and forest ecosystems of south-central Alaska. Special Issue, Forest Ecology and Management 227(3): 193-283.

 

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