Monday, February 16, 2015

Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest

     Recently, California has been plagued by droughts caused by improper water management as well as atmospheric blocking of high pressure weather. This is a major problem because the central valley of California is one of the biggest agricultural producing areas i the US. Beyond an economic impact, these droughts also have an ecological impact when forests die or change composition due to less moisture increasing temperatures.

     In this study, a team used aerial photography and LIDAR to map out the density and health of Bishop pine populations on Santa Cruz Island off the coast near Los Angeles. They took information such as precipitation and cloud coverage and compared it to models which had tree density and height in order to see how the drought affected the forest. They determined that larger trees located in medium elevations that were partially concealed by fog survived the drought more readily. Surprisingly, trees in the center of the island did not fair so well, in part due to higher elevation as well as having no cloud cover due to being on the leeward side (behind the mountain). The innovative thing done in this study was that dead trees where found by differentiating LIDAR models of trees with dead canopies; basically, the radar did not reflect off of leaves and this allowed them to find clusters of trees that had only died because of the recent drought.
     Using this kind of refined methodology we can create programs that tailor to specific species of trees in order to map out drought effects on natural ecology. Since this study focused on Bishop pines on one Island, maybe we can use their models to map out other pine species along the coast of California. It would probably be easy to map larger trees such as redwoods in coastal state parks such as Big Sur.   

    Graph made using data from a LIDAR elevation model and aerial photography. Taking the information from all eight graphs allows us to "paint a picture" of Santa Cruz Island and see the effects of droughts.  

     Graph showing the mortality of the Bishop pine on Santa Cruz Island during recent droughts in Southern California.

     Source: Baguskas, S. A., Peterson, S. H., Bookhagen, B., & Still, C. J. (2014). Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest. Forest Ecology and Management315, 43-53.


  1. Have the researchers been able to compare the amount of dead canopy today to historical numbers in order to determine the severity of the current problem?

  2. Based on the research made through the LIDAR map prior to the drought, how early on were the population of the trees taken?

  3. I have to wonder how many factors of causes of death of the trees the researchers included in their study. Surely the drought had an impact, but couldn't the ages of the trees, diseases, and animal interactions also have contributed to the decline in population?