Northwest tree scienceon October 18, 2013 @ 3:08 pm (Updated: 3:23 pm - 1/21/14 )
Trees actually change color, explains Anthony Moran from Superior Northwest, because of photosynthesis.
Photosynthesis, or how trees eat, is heavily dependent on the type of light trees receive. The chemical reaction takes place, in part, due to chlorophyll. When the light is steady and bright, as it is in spring and summer, the chlorophyll within the trees' cells is very strong and overpowers other types of pigmentations. When the light changes and the temperature drops, the chlorophyll becomes inactive, letting other pigments such as carotenes and xanthophylls show through. Carotenes give trees their orange color in the fall, while xanthophylls give trees the bright yellow.
Anthony says that Seattle's fall is actually not conducive to the brilliant fall colors. Bright, sunny days with cold temperatures leave the trees looking prettier, where Seattle's steady decreases in temperature just turn the green leaves brown.
The rainy weather also makes trees susceptible to pathogens which can make trees structurally unsound. These pathogens occur naturally in the soil, water, and rain.
Anthony says the most vulnerable tree is the evergreen, which is prolific throughout the Northwest. Pathogens can attack the tree and make it hollow from the inside out. Trees that become hollow are structurally unsound and can potentially fall on houses, cars, or property.
He recommends having an ISA-certified arborist check your trees on a regular basis to protect your property and your trees.