Early leaf color change could be from root damage in 2012 North Country drought
Monday, September 1, 2014 - 7:51 am


If there was a contest among trees for earliest leaf color change, the winners would be losers.

Early leaf color change is a reliable indicator of failing health; the worse a tree's condition, the sooner it begins to turn. Although the display of colors our hardwoods produce each autumn never fails to fill me with awe and appreciation, this year I have observed widespread leaf color change in northern New York beginning in early August. It is especially noticeable in roadside trees, which experience perennial stress from road salt as well as root restriction, but I have observed this even in forest lands.

Even now, two years later, trees are still declining as a result of the summer drought of 2012 when soil moisture dropped to the lowest levels since record keeping began. This was partly due to the scant summer rainfall, but also because of low humidity, high temperatures, a very high UV index, and frequent and persistent winds.

Under those conditions, tree roots actually died back, beginning with the fine absorbing roots a few inches below the surface. Most people, myself included, are surprised when they learn that ninety percent of tree roots are in the top ten inches of soil, and that very few roots penetrate beyond eighteen inches deep. Knowing this, it's easy to understand how tree roots can run out of moisture in a drought.

A sort of Catch-22 situation happens as a result of root dieback. All the starches stored in the affected portions of the root system root are lost, so the tree has less energy the following year. But that's when it needs extra energy to re-grow its roots. And because its roots are compromised, the tree can't get adequate water and nutrients.

Dr. George Hudler from the Plant Pathology Department at Cornell says that it takes a healthy tree two to three years to recover from a significant drought. But what about trees whose health was less than stellar to begin with? Most, though not all, of the leaf color change I observed in late July was on roadside trees. Those unfortunates are subject to road salt, root zone restriction, reflected heat from pavement, and in most cases, turf grass, which gobbles up all but the heaviest rains. It's no shock that these are the ones that turn color first, but it was jarring to see it in July.

Knowing the significance of early color can be disconcerting, but it's also an opportunity to see how the trees around your home are doing. Those that have almost completely turned color by late August are probably not long for this world, and it's time to consider their removal and replacement in the next few years. Color change of fifty percent or less indicates probable decline, but certainly severe stress. Providing supplemental water (one inch over the root zone per week) to these tree over the next few years may help keep them around longer. Mulching the root zone, which is twice the branch length, two to four inches deep in lieu of grass will also help at least as much.

When fall does get here, I hope we can still enjoy autumn colors as much as we used to.

Paul Hetzler is a forester and Cornell Cooperative Extension of St. Lawrence County horticulture and natural resources educator.