Slide show - Beetles

  • blowdown patches In 2003 a large windstorm blew down trees across several thousand acres in the Cedar River Municipal Watershed. Individual trees were blown down and some canopy gaps were created. This gap is about 16 acres.
  • blowdown in forest Large Douglas-fir trees serve as hosts for the native Douglas-fir beetle. When many Douglas-fir trees are dead or injured, the beetle population can increase, possibly resulting in more tree mortality.
  • bark beetle galleries Beetles bore under the bark to create tubes where they lay their eggs. Larvae then eat their way back out of the bark, creating the network of tubes called galleries.
  • nurse log Entomologists assessed the situation in the field and agreed that resulting tree mortality would not be extreme. Since down wood is a critical ecosystem component and wind is a natural disturbance, we left the down wood for habitat for insects, small mammals, fungi, and eventually young trees.
  • beetle trap To understand the impact of all the fresh down wood, we set up traps baited with an attractant pheromone to catch beetles. Once the beetles fly into the funnels they fall into the cup at the bottom.
  • beetles in trap cup The cup at the bottom of the trap is filled with propylene glycol, which prevents carnivorous beetles in the trap from eating the bark beetles. Volunteers empty the traps weekly and count the bark beetles.
  • df beetle traps We found that beetle levels began to drop after their first peak year in 2005. However, they unexpectedly rose again in 2008. Additional sampling in 2009 and 2010 showed that they again continued to decrease as anticipated.
  • df beetle mortality We found that beetles did kill more trees than normal in 2006, but that tree mortality went down in subsequent years. A tree-mortality spike in 2009 is likely driven by the beetle-population increase in 2008. The pattern of tree mortality (small clusters scattered throughout the forest) adds to forest structure and wildlife habitat in positive ways and returned to pre-windstorm levels by 2010.