Nov 19, 2015

Recent Tree Mortality in the Western United States from Bark Beetles and Forest Fires

Hicke, Jeffrey A., Meddens, Arjan J.H., Kolden, Crystal A.
Forest Science
  • States that forests are substantially influenced by disturbances, and therefore accurate information about the location, timing, and magnitude of disturbances is important for understanding effects
  • States that in the western United States, the two major disturbance agents that kill trees are wildfire and bark beetle outbreaks
  • Aims to quantify mortality area (canopy area of killed trees), which better represents impacts than affected area (by beetles) or burn perimeter area, and characterize patterns in space and time
  • Bases estimates on aerial surveys for bark beetles and the Monitoring Trends in Burn Severity database (from satellite imagery) for fires
  • Finds that during the last three decades, bark beetle-caused mortality area was 6.6 Mha (range of estimates, 0.64–7.8 Mha; 7.1% [0.7–8.4%] of the forested area in the western United States) and fire-caused mortality area was 2.7–5.9 Mha (2.9–6.3%)
  • States that although large outbreaks and fires occurred before 2000, substantially more trees were killed since then
  • Finds that in several forest types, mortality area exceeded 20% of the total forest type area
  • Mortality area estimates allow for comparisons among disturbance types and improved assessment of the effects of tree mortality