Why Flagstaff’s iconic aspen forests are dying out

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The aspen forests in Flagstaff are struggling due to climate change, but NAU researchers hold hope for recovery.

A groundbreaking 20-year study has revealed a troubling future for Arizona’s iconic aspen trees as climate change continues to reshape forest ecosystems. Northern Arizona University researchers have uncovered alarming mortality rates among young aspens on the San Francisco Peaks, signaling potential long-term consequences for forest biodiversity and ecosystem health.

Climate change threatens aspen survival in northern Arizona

Northern Arizona University’s Ecological Restoration Institute (ERI) has documented a concerning 42% mortality rate among aspen trees in their study area, with younger trees showing particular vulnerability to environmental stressors. The research, published in Forest Ecology and Management, tracked aspen populations across 135 permanent plots from 2000 to 2022.

“One key misconception we sought to address is the belief that the impacts of climate change on aspen trees are solely related to temperature increases,” said Michael Stoddard, the study’s lead author and ERI research associate. “While rising temperatures and prolonged droughts are critical factors, the interplay of these elements with disturbances like fire and browsing is equally significant.”

Multiple threats create a “bottleneck” effect

The study identified several concurrent challenges facing aspen populations:

  • Prolonged drought conditions, including the Western megadrought
  • Wildfire impacts from multiple fires (Schultz, Museum, Pipeline, and Tunnel)
  • Grazing pressure from Rocky Mountain elk
  • Temperature increases affecting lower elevation populations

While researchers observed a 13% increase in overall aspen regeneration, particularly in moist areas, young trees consistently failed to reach maturity. This “bottleneck” effect threatens the long-term sustainability of aspen populations, as older trees aren’t being replaced by new growth.

Hope for forest management solutions

Despite the concerning findings, researchers have identified potential paths forward. The aspen population’s positive response to the 2022 Pipeline fire suggests that carefully managed interventions could help protect these important trees. Stoddard emphasized the need for collaboration between ecologists and forest managers to develop effective conservation strategies.

“Without a balanced age structure, the forest lacks resilience,” Stoddard explained. “Mature trees provide stability, but they won’t last forever, and there are not enough younger trees to replace them over time.”

 

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