For background information and additional context, see our Tree Mortality and Fire page.
California is in the midst of a prolonged drought, which has caused unprecedented levels of tree mortality. CAL FIRE estimates that drought has killed 29 million trees across the state in recent years, and impacts have been equally or more severe in other parts of the southwestern United States. Drought causes tree mortality in two major ways: either by directly killing trees, or by making trees more vulnerable to insects and pathogens (van Mantgem et al. 2016). Drought also has close ties to climate change; although drought is often defined by reduced precipitation, it also magnified by high temperatures, which lead to increased evapotranspiration that causes additional tree stress (Adams et al. 2009). Studies indicate that chronic drought caused by climate change could be the underlying cause of increased tree mortality in the West (van Mantgem et al. 2009). In early 2016, Governor Brown formed a Tree Mortality Task Force, and efforts are underway to mitigate drought-related tree mortality and fire hazard. For more information on drought and fire:
California’s Tree Mortality Task Force: http://www.fire.ca.gov/treetaskforce/
Adams, H.D., Guardiola-Claramonte, M., Barron-Gafford, G.A., Villegas, J.C., Breshears, D.D., Zou, C.B., Troch, P.A. and Huxman, T.E., 2009. Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought. Proceedings of the national academy of sciences, 106(17), pp.7063-7066. http://www.pnas.org/content/106/17/7063.full
Van Mantgem, P.J., Stephenson, N.L., Byrne, J.C., Daniels, L.D., Franklin, J.F., Fulé, P.Z., Harmon, M.E., Larson, A.J., Smith, J.M., Taylor, A.H. and Veblen, T.T., 2009. Widespread increase of tree mortality rates in the western United States. Science, 323(5913), pp.521-524. http://www.fs.fed.us/pnw/pubs/journals/pnw_2009_vanmantgem001.pdf
van Mantgem, P.J., Caprio, A.C., Stephenson, N.L. and Das, A.J., 2016. Does prescribed fire promote resistance to drought in low elevation forests of the Sierra Nevada, California, USA?. Fire Ecology, 12(1), pp.13-25. http://fireecologyjournal.org/docs/Journal/pdf/Volume12/Issue01/013.pdf