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Early leaf fall? Crazy weather stresses trees, too

Jessica Walliser
| Friday, Sept. 14, 2012, 8:58 p.m.
Tulip poplars are among the trees dropping leaves early this fall.
Credit: Jessica Walliser
Tulip poplars are among the trees dropping leaves early this fall. Credit: Jessica Walliser

The crunch of leaves under our feet is nothing new to Western Pennsylvanians.

However, you might have noticed that the crunching sound is happening a few weeks earlier than usual. And, we haven't even enjoyed any of our beautiful fall foliage yet.

So, what gives? Why are so many deciduous trees dropping a portion of their leaves so early this year?

It's a one-word answer: stress.

With the crazy weather conditions we had this season, our trees are showing signs of stress. Early spring heat caused many trees to leaf out prematurely, then a mid-spring cold snap sent them into a deep freeze. Not to mention the stress caused by this summer's excessive heat, coupled with no rain to speak of for several weeks.

Tiny pores in a leaf's surface help regulate moisture levels within the plant and, because these pores can't completely close, trees use premature leaf drop as a way to stave off excessive moisture loss during periods of drought and/or stress.

They drop the leaves they don't need in order to prevent unnecessary water loss though those pores and to use whatever water they do have more efficiently. Early leaf drop is the tree's way of protecting itself from further damage.

Some trees are more prone to premature leaf loss in times of stress and, in my yard, it is most evident on the tulip poplars and sycamores. Deeper rooted trees, like oaks, are less likely to drop their leaves early, as are needled evergreens like pines and spruces.

In most cases, a single year of stressful drought conditions will not cause branch dieback or tree death, but several years of drought can cause an increase in tree mortality rates in our managed landscapes and in the woods. Even a single year of drought conditions, though, can make trees more susceptible to damage from other stressors, including pests and diseases.

Maintain the health of your trees by having an arborist certified by the International Society of Arboriculture pay a visit every few years. They are trained to spot insects and diseases before they become problematic, and they can help teach you how to properly care for all your trees.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is

Send your gardening or landscaping questions to or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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