President’s Note: Oak Trees

president's note nature oaks

I have always been interested in forestry. One major component of the forests I grew up with and see here at the Kerr Center Ranch are oak trees. To say they are an important part of the forest ecosystem would be an understatement.

Oaks provide mast for wildlife, and, historically, indigenous people used oak mast as a food source. We use oaks for durable, long lived shade trees around our homes and the lumber is excellent (depending on the species) for furniture.

I read a recently published book entitled The Nature of Oaks, by Douglas Tallamy. The book is broken into chapters based on the months of the year, and explores how oaks, insects, birds, and other wildlife use the oak trees in our landscapes and forests throughout the year.

One thing I learned was how many caterpillars overwinter in the bark of oak trees. The birds you see going up and down the bark in the winter are searching for those overwintering caterpillars!  A chickadee’s diet in the winter can be 50% insects. So, many of the birds who visit your bird feeder in the winter still need insects as part of their diet – which oak trees provide habitat for.

Another component of food production provided by oaks is, of course, acorns, or mast. It is important for some birds as well as squirrels, deer and turkey. I have been asked if fertilization increases acorn production in oak trees, and the surprising answer is no – based on research from Tennessee.

The study identified 120 white oak trees and measured mast production over three years (2006-2008). According to a synopsis of that part of the study, basically, 33% of the trees were good mast producers, 19% moderate, and 48% poor. Nearly half of the oaks produced little or no acorns!

The study went on to fertilize the trees and to conduct a release (removing poor producers to make room for the good producers to expand their canopies). Fertilization seemed to have little or no effect. Canopy release had a greater effect on increasing mast production.

Basically, identifying and managing the forest to favor high mast producing trees has a greater effect than just fertilizing. This also has the added benefit of increasing regeneration of oaks, since more acorns are produced.

One aspect of oaks that has fascinated me from a sustainability standpoint is their lifespan, which is measured in hundreds if not over a thousand years, depending on the species. White oaks can live five to six hundred years.

We talk about the importance of crop rotation and amending the soil with nutrients to sustain crop production over the long term, yet an oak tree can grow in one spot for over 500 years and still produce an acorn crop without fertilizer. How is this possible? I think science is still trying to answer that question. Is it due to soil mycorrhizae, or some other aspect of the soil in combination with climate that we do not yet recognize?

Douglas Tallamy mentioned in the epilogue the growing evidence that historically, the eastern deciduous forest may have resembled a savannah and been more open than the forest we see today. If this is true, it would have been beneficial to oaks from a canopy size and mast production standpoint, and it makes sense based on the results of the study cited on oak crown release to improve the health and productivity of an oak stand.

The Oklahoma Native Plant Society is hosting presentations by Doug Tallamy on February 4-5 in Oklahoma City and Tulsa. Be sure to check it out if you are interested in hearing the author of The Nature of Oaks.

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