I received this question from Michael Sisson:
I was just noticing that the local trees are looking like they're starting to change color this morning and then I found a fresh leaf that suggests I'm right. What do you think? Look around at 14th and Salem St in Lafayette.
Thank you for the question!
A lot of factors can make trees begin to show some early bits of color from soil issues to air pollution to disease, & insect pressure, etc. Too early color production is often a sign of some sort of stress. Without seeing the sites around the particular trees that are showing a bit of color.
Indeed, trees normally begin to cut back or stop growth by mid to late August & may cut back on chlorophyll (gives leaves their deep green color) production in preparation for dormancy months away. Most have already grown all they are going to grow by mid to late August (for the summer), unless they are trimmed, then they sprout back. Suckers may also appear around certain trees.
A stressor will begin to affect a tree more later in the growing season if the stress has been cumulative. Active growth & continued issues with that stressor may make symptoms of that stress really begin to show up.
From a weather standpoint this summer, only 40-75% of the normal rainfall has fallen in much of our area since early July after a dry May & several dry stretches in June. We tend to get a lot of our summer rainfall from storms & especially severe weather. Severe weather occurrence is the lowest for any summer since 1970 in our viewing area. In that summer, just 3 reports of severe weather occurred. 1988 was very inactive until we had a couple of severe weather events/outbreak August 15 & 18 with multiple severe weather reports over the viewing area.
Some of the color may be tied to the non-consistent rainfall causing just a lot of fluctuation in soil moisture. Some species handle it better than others.
Non-consistent rainfall can also cause Pin Oaks to really turn yellow. Without the slightly-acidic rainfall, higher soil pH develops in areas where limestone products for construction or the deep, more calcareous glacial till is dug up & mixed with the topsoil. Pin oaks do not handle calcareous soils or soils with higher pH well. Ironically, if a Pin Oak is watered too much with hard, cholorinated tap water, it gets chlorosis. It is native to wet soils, but does best in acidic soil. Hard, chlorinated water & dry soil or highly-flucating soil moisture is not best for it.
On a side note, more Blue Ash & Chinkapin Oak should be planted as street trees in our area. They handle the soil fluctuation a lot, hard, chlorinated water well, as well as the calcareous & high pH soil that is often found around construction sites where the unleached deep glacial till is mixed with the topsoil & limy construction material alters the pH. Blue Ash is also more resistant to the Emerald Ash Borer than Green & White Ash, which are more traditional street ashes.
In summery, it is some stress that may be attributed to rapid soil moisture conditions or overall lack of consistent rainfall.