EPOW - Ecology Picture of the Week

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Microburst Deadfall

Credit & Copyright:  Dr. Bruce G. Marcot

  

Explanation:  While hiking the trails in this forest of Douglas-firs and Ponderosa pines in the Sky Lakes Wilderness of southwest Oregon, we happened upon this odd scene.  Something had punched a big, nearly circular hole in the dense forest canopy, and beneath lay this "jackstraw" of trees pummeled to the ground.   The culprit?  Most likely a microburst windstorm that leveled this particular part of the forest, leaving the surrounding trees unscathed.   A microburst is an intense column of air that suddenly funnels downward with devastating force.  Often, microbursts are far larger.  For example, one in 1989 leveled hundreds of trees in the Rock Creek area near Clinton, Montana.  Another took down 6 million trees near Steamboat Springs, Colorado, in 1997.  Often, when trees are downed by wind to this extent, they are salvage-logged, meaning that they are removed from the forest for their timber before they have a chance to decay and potentially attract harmful forest pest insects such as bark beetles.  However, in this case, the area was small and located within an official wilderness where motorized vehicles are prohibited.   And, most important, this is a natural process, and wildernesses were designated to maintain such dynamics and processes.  Down wood, as well, provides important habitat for many wildlife species such as marten and fishers that use hollow logs as den sites, and grouse that display on top of the logs.   As the logs slowly decay, they also serve as "time-release" sources of nutrients for the forest soil.  And the forest opening will soon be colonized by early-successional herbs and shrubs that diversify the forest floor and add to habitat for many species of birds and invertebrates.      Not a disaster, here in this wilderness.       Information:      Abe, T., Y. Kubota, K. Shimatani, T. Aakala, and T. Kuuluvainen. 2012. Circular distributions of fallen logs as an indicator of forest disturbance regimes. Ecological Indicators 18:559-566.      Attiwill, P.M.  1994.  The disturbance of forest ecosystems: the ecological basis for conservation management.  Forest Ecology and Management 63(2-3):247-300.      Brazee, N. J., D. L. Lindner, A. W. D'Amato, S. Fraver, J. A. Forrester, and D. J. Mladenoff. 2014. Disturbance and diversity of wood-inhabiting fungi: Effects of canopy gaps and downed woody debris. Biodiversity and Conservation 23(9):2155-2172.      Johnson, E.A., and K. Miyanishi, editors.  2007.  Plant disturbance ecology: the process and the response.  Elsevier Academic Press.      Ulanova, N.G.  2000.  The effects of windthrow on forests at different spatial scales: a review. Forest Ecology and Management 135(1-3):155-167.