Tom's Blog

Friday, October 7, 2011

Fall color at its peak

Yesterday the Conservancy had outstanding color, probably the best I have ever seen; today is equally good.

Oaks are not as colorful as maples, but they are often more variegated, with a single tree providing green, yellow, orange, and red. Hard to believe that the red above is from a white oak, since other whites in this same area are dull brown. The color of an individual tree probably depends a lot on age, position in the forest, and health.

One species of oak that seems to be consistently colorful is Hill's oak (Quercus ellipsoidalis), and we have quite a few smaller trees of this species. In fact, we had misidentified some of these trees when we constructed our tree database (calling them black oaks), but black oaks are never as colorful as the specimen shown in the photo at left.

Hill's oak, also called northern pin oak, is unique to the upper Midwest, and is mainly found on drier sites. According to the information, it occurs primarily on acidic sites, which agrees with our observations, since the pH of the soil near the tree to the left is less than 6. It is a member of the red oak group, which includes oaks with pointed leaves.

The species name (ellipsoidalis) was given because the acorns are ellipsoid in shape, and the common name comes from Chicagoan E.J. Hill, who first described this species in 1899 (Hill, E.J. 1899. A New Biennial-Fruited Oak. Botanical Gazette , Vol. 27, 204-208 plus two unnumbered pages of illustrations).

The other tree species that provides a lot of color is shagbark hickory, Carya ovalis, which forms intensely yellow leaves. This species is fairly common in our more open savannas, and provides great contrast with the oaks.

Black walnuts (Juglans niger), on the other hand, provide no color at all, since they have already lost their leaves. Another species that provides no interesting color is bur oak (Q. macrocarpa), whose leaves get mostly a dull gray-green. This species also loses its leaves early. They are half gone already and will be gone before the end of October.

The unusually warm, dry air is reminiscent of so-called Indian summer, but coming a bit early. According to the National Weather Service, there is an elongated area of relatively high atmospheric pressure over the region, being blocked by a polar trough to the west.

We are very close to a record high temperature. (Two years ago, when we had our landowner's forestry field day about this time, it snowed!)

If this weather had come a month later it would be ideal for the prescribed burns we are planning for early November.


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