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      Earth Gauge: Weather's Influence on Fall Foliage

      Fall foliage tourism across the country is a highly profitable industry, bringing 460 million dollars in revenue to Vermont alone. According to the U.S. Forest Service, fall tourism brought eight billion dollars in revenue to New England in 2011. Foliage changes color during the transition from summer to fall. Weather influences the amount and brilliance of color in autumn leaves ?? temperature and moisture affect color and leaf senescence (aging from a mature state to death). A moist growing season followed by dry sunny days with cool nights produce the best fall colors, but varying combinations of temperature and moisture make each autumn unique. Extreme weather events can affect fall foliage in a number of ways:

      Drought stress during the growing season can trigger leaves to drop prematurely, before they develop fall coloration. Heavy winds and severe thunderstorms can cause leaves to fall before they change colors. Freezing conditions, especially early frost, destroys a leaf??s ability to produce red and purple colors. Hurricanes can destroy trees and their foliage. For example, hurricane Irene deposited salt on trees many miles inland, causing cell and tissue damage to leaves. Wildfires, depending on their severity, can destroy the forest canopy. Warmer temperatures due to climate change have delayed leaf coloring and leaf drop. Satellite observations indicate a delayed fall senescence of up to 4 days per decade in European and North American temperate forests since 1982. Warming temperatures in Greenland have increased the cover of green vegetation and delayed fall senescence by more than two weeks. Climate change impact on boreal forests is uncertain, as it delayed fall senescence in Eurasia, but sped up senescence in northern Canada and Alaska from 1982-2008. Warming temperatures have also been associated with earlier onset of spring ?? the combination of an earlier spring and a delayed fall season has increased the active growing season.

      Use this illustration to identify trees and their fall foliage where you live (click image to download high resolution).

      (Source: Richardson, A.D., T.F. Keenan, M. Migliavacca, Y. Ryu, O. Sonnentag, and M. Toomey. 2013. Climate Change, Phenology, and Phenological Control of Vegetation Feedbacks to the Climate System. Agricultural and Forest Meteorology. 169:156-173. and United States Forest Service. News Release No.1134: USDA Forest Service Launches Expanded Fall Color 2011 Website. Accessed online 1 October, 2013. http://www.fs.fed.us/news/2011/releases/09/fall-colors.shtml and Wiltshire, J.J.J., C.J. Wright, M.H. Unsworth, and J. Craigon. 1993. The Effects of Ozone Episodes on Autumn Leaf Fall in Apple. New Phytol. 124:433-437. and United States Forest Service. Science of Fall Colors. Accessed online 1 October, 2013. http://www.fs.fed.us/fallcolors/2013/science.shtml and Rogstad, A. 2002. Recovering from Wildfire. University of Arizona. Accessed online 1 October, 2013. http://ag.arizona.edu/pubs/natresources/az1294/ and Platt, J. 2013. Yes, Vermont Has a Leaf Forecaster. Mother Nature Network. Accessed online 1 October, 2013. http://www.mnn.com/lifestyle/eco-tourism/stories/yes-vermont-has-a-leaf-forecaster and Deedler, W.R. 2007. Faster Fall Foliage? National Weather Service. Accessed online 1 October, 2013. http://www.crh.noaa.gov/dtx/foliage.php)