A new study suggests that California’s largest trees have declined by more than 50 percent. In parts of southern California, trees larger than two feet in diameter, have declined by more than 75 percent. The study, led by Patrick McIntyre of the California Department of Fish and wildlife, suggest that the loss of California’s giant trees is primarily due to increasing temperature and the resulting water shortage. By 2100, California’s average temperature is projected to increase by 9°F, raising the overall water stress for the trees by as much as 30 percent.
Increasing temperatures have resulted in more water being lost to evaporation and earlier melting of snowpack. This drastically reduces the total amount these trees need during the driest months of the year. Large trees also play an integral role in the natural management of the ecosystem. They produce more seeds, store more carbon, provide homes for small native animals, and naturally resist the forest fires the rage across the state every year.
Although it is not clear why, large trees appear to be extremely vulnerable to water shortage. Jim Lutz, a Utah State University forest ecologist, suggests that it may be due to the internal hydraulic system of the large roots, which have a tendency to fail during a drought. Another hypothesis is that large trees, having sprouted centuries ago, were much more adept to a milder California climate.
The study presents a challenging and grim future, says William Anderegg, a Princeton University forest ecologist. “The loss of these majestic trees is a pretty emotionally powerful thing to think about. These are often the trees that have been around for thousands of years. It’s kind of a less magical future having lost those trees.”
 Cornwall, “California’s Forests: Where Have All the Big Trees Gone.” http://news.nationalgeographic.com/news/2015/01/150119-california-forests-shrinking-climate-drought-science/