In short, winter has a significant impact on the primary growing season for these mountain trees, because moisture is continually available from rain or snow, the tree root zones don't freeze, and there is enough sunlight for photosynthesis. The trees slow down during the pre-monsoon dry season in May and June when water is scarce, and then quickly respond to the sudden availability of water at the onset of the monsoon in July.
As unlikely as it may seem, Arizona does experience a monsoon every summer. Certain roads have yellow warning signs posted -- "Do Not Cross When Flooded." Though these signs may seem out of place in the middle of a desert, they have a serious purpose. In Arizona, as in other regions of the world such as India, residents must cope with a season of high temperatures, high winds and high moisture, resulting in potentially deadly weather.
The Arizona monsoon usually begins around July 7 and continues for the next two months, resulting in about one-third of the region's yearly rainfall. The monsoon varies from year to year in starting date, duration and intensity.
"The semi-arid forest ecosystem adapts to the extremes in the annual cycle of water availability by its ability to remain turned on during the winter," Brown said. "Water stress, rather than temperature, is the primary control on the forest's behavior. The trees will remain significantly active regard