News Release News Release The City of Palo Alto
Communications Department
250 Hamilton Ave
Palo Alto, CA 94301


PRESS RELEASE 11/17/2009
Subject :

Fall Leaf Colors Offer Brilliant Hues
Contact : Dave Dockter, Landscape Specialist, Planning and Community Environment Department    650-329-2441
Palo Alto, CA -- In many parts of the United States, people are enjoying one of nature's finest natural beauty events— leaf color change that signals a tree’s response to temperature change and the seasonal bridge from summer to fall.  Throughout Silicon Valley, and especially in Palo Alto, color-changing leaves make for a beautiful display seen on virtually every street.  

"This autumn has produced some of the best seasonal fall color displays of recent decades, “says Dave Dockter, Landscape Specialist for Palo Alto’s Department of Planning and Community Environment and a Canopy contributing member. “Beautiful color change is not an anomaly—it is a very systematic event. The tree is a living system."

Why do trees change color?
The leaves of deciduous plants, which can be thought of as small factories containing raw materials and sugars, all in chemical form and with color, begin shutting down for the year when triggered by cool climate events.  As the leaf is slowly “abandoned” by the tree, green chlorophyll - the dominant chemical found in most leaves - is broken down and “recycled” by the tree, unmasking other-colored chemicals.  The disintegration of green chlorophyll unmasks the more stable yellow to orange carotene of the leaf. In some trees the leaf chemicals change the red to burgundy pigments. The leaves of other trees may assume various shades of yellow, orange, crimson, purple or red separately, even variations of all colors on the same tree.

“The best autumn colors show up when a moderate rainfall occurs in early November, which coincidentally, we have already experienced,” says Dockter. “This year in Palo Alto, we have had the perfect weather for a brilliant Indian Summer or autumn season fall effect.  When several elements occur together, particularly bright colors can be expected.”

Leaf color change in trees may appear more dramatic in some trees than in others. While a species such as American Sweet Gum can provide lovely fall color, the timing of the change in leaf-color can be a used as a diagnostic signal--indicating it may be stressed by drought, insects or disease.

“Trees often display signals that reflect a response to a problem agent, and if they are ignored or continue unnoticed, consequences can become worse. If the leaves on your trees seem to have changed color much sooner than similar trees in the area, then you may want to consult a professional arborist who can identify problems and offer possible solutions,“ added Dockter.

Premature colors can be an indication that a tree isn’t strong enough to withstand the usual changes that occur when the weather turns cold and dry and daylight hours become shorter.  Drought-stressed trees usually turn color earlier than healthier trees that enjoy adequate water supply.

“Trees respond to temperature, light and water changes by seasonally shutting down their above-ground growth but continue growing their root system,” adds Dockter.  “Even in colder regions, root viability can be helped by the upper soil layer acting as temporary insulation with heat-saving properties. But, this should be the exception. This year, great fall color is evident everywhere.”

Where to look?
There are some local spectacular fall tree color locations on Dockter’s must-see list every year. According to Dockter, the best spectacular golden canopy and carpet of the mature Maidenhair Ginkgos’ are along Greenwood, Ramona at Addison and Lincoln, as well as in the landscape design trees of Genencor visible from 955 Page Mill; the rust and yellow leaves of Sawtooth Zelcovas on Bryant; vibrant orange-yellow of Boston Ivy on the old walls of the Lanning Chateau at 325 Forest; the fiery red of the Dawn Redwood at the Main Post Office at 380 Hamilton; the festival of colors Chinese Pistache on Cowper, south of University and Waverley at Embarcadero; the Sour Gums and other trees at Gamble Gardens; the American Sweet Gums along Page Mill Road between El Camino and Foothill Expressway; the Red Oak at Lucie Stern Community Center front lawn; and the young Shumard Oaks on Porter Drive at Page Mill Road.  

To find out more about Palo Alto’s colorful trees, visit www.cityofpaloalto/environment/ or, or call Canopy at 650-964-6110.