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The USA Going Green

Why Are Our Trees Turning Fall Colors So Early?

Many of the deciduous trees around Portland appear are showing fall colors much earlier than usual. While trees may get a jump on the season for various reasons, this year’s early debut of autumnal hues is being attributed to the Pacific Northwest’s unusually dry, hot spring and summer.

Drought in Oregon and Washington has been plaguing the area for months. The dry conditions have the most severe ramifications for farmers and fish, but they also take a toll on city and suburban trees, lawns and gardens. Lawns are brown, and many trees are under stress.

Why Trees Turn Colors

Fall colors are a prelude to a tree’s dormant season. Dormancy is a plant’s normal adaptation to cold weather and short daylight hours. During spring and summer, chloroplasts power growth. They contain chlorophyll, a green pigment that captures light for photosynthesis. Along with water and carbohydrates, chloroplasts keep trees healthy and green during the growing season.

As growth winds down and daylight hours dwindle, leaves begin to change color. The amount of chlorophyll diminishes and allows leaves to show other colors. Carotenoids and xanthophyll are brown, yellow or orange pigments. These substances are present but masked by chlorophyll during summer.

Anthocyanins are red, purple and blue colors produced in reaction to stress and are generally only seen in autumn. They protect leaves from excess light and plant cells from dropping temperatures. Eventually, as dormancy progresses, the only pigments remaining in leaves are brown tannins.

Adequate water during spring and summer followed by a dry fall with warm days and cool nights are the ideal conditions for brilliant fall colors.

How Drought Affects Leaf Color

Heat and drought stress can push trees into early progress toward fall colors. If trees aren’t receiving enough water, they quit producing chlorophyll and leaves lose their green color. Heat adds to the problem by increasing the trees’ loss of water, or transpiration.

An early end to the growing season is bad news for trees because they don’t gain and store the energy they need to thrive. A severely drought-stressed tree may drop its leaves before they turn colors, or the leaves may turn brown and dry while remaining on the branches.

Other Reasons for Early Color

Any stressors can limit a tree’s carbohydrate production and lead to a premature start of the off-season cycle. Stress from limb loss, pests, soil compaction and other environmental conditions are common causes of unhealthy or dead trees.

Maintaining normal moisture by watering during the summer limits the effects of drought and heat, but if a tree is too damaged, it may not recover. If a tree dies, it’s best to have it removed before it can topple and hurt people or damage property.


About the Author:

Lorin Fielding has been in the landscaping business since 2003. Since then, he has opened his tree services business Inexpensive Tree Care. Honesty, value and reliability are the founding principles Lorin instilled into this business and his expertise is constantly growing along with the industry.

1 Comment for “Why Are Our Trees Turning Fall Colors So Early?”
  1. Maybe the fall colors are early, but the thing I find curious is that so many trees are displaying a single branch of VERY intense fall colors, while the rest of the tree - more than 80-90 % - is still full green. What’s going on?

    Posted by Francene | September 21, 2015, 8:03 pm
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