Oaks Are Mighty

Planting an oak tree in your yard can do more for wildlife than a perennial border of native plants.

Oaks are a keystone species. They profoundly influence other species in our forests. North American oaks provide food and shelter for more species than any other tree group and form the backbone of many different forest communities. Here in Connecticut, there are 470 species of Lepidoptera (butterflies and moths) whose larvae eat oak leaves.

This Funerary Dagger Moth larva (Acronicta funeralis) is just one of the 470 species that feed on oaks.

Having a bunch of larvae, or caterpillars, eating the leaves of your oak tree may not appeal to you, but if you are a bird, it certainly would! More than 90% of forest-nesting birds feed butterfly and moth larvae to their young. The woods across from our house are filled with Northern Red Oak (Quercus rubra) and White Oak (Quercus alba) trees. In early May, these trees are loaded with neotropical birds like warblers, whose migration is perfectly timed with the larval hatch.

The Charter Oak, oil on canvas, Charles De Wolf Brownell, 1857, Public Domain. Wadsworth Athenaeum.

The Charter Oak was a very large White Oak which grew on Wyllys Hyll in Hartford. It may have dated back to as early as the 12th century but succumbed to a wind storm on August 21, 1856. Legend has it that Connecticut’s Royal Charter of 1662 was hidden in a hollow of the tree to keep it from being confiscated by the English governor-general. This symbol of American independence is commemorated today on the Connecticut State quarter.

Acorns are falling from trees now. This year doesn’t seem to be a mast year. In a mast year, which happens every few years, oaks produce far more acorns. This could be because larger numbers of acorns might overwhelm predators and ensure more acorns germinate and survive.

Northern Red Oak leaves have pointed lobes and rounded acorns with a cap which looks like a fedora. Photo by Dcrjsr / CC BY (https://creativecommons.org/licenses/by/3.0).

White Oak acorns germinate immediately on falling into the leaf litter, whereas Northern Red Oak acorns need a cool, moist period and won’t sprout until the spring.

White Oak leaves have rounded lobes and oblong acorns with caps which extend lower than red oak acorns, like ski hats. Photo by Alouis21 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0).

Did you ever wonder why there are more red oaks than white oaks? You can thank an Eastern Gray Squirrel (Sciurus carolinensis). Acorns from the Northern Red Oak have more tannin, a bitter chemical that protects the acorns from insects and other predators. White Oak acorns have less tannin and so are “sweeter.” Peter Smallwood, associate professor of biology at the University of Virginia, and Michael Steele, professor of biology at Wilkes University, have found that squirrels eat 85% of white oak acorns shortly after finding them, but store about 60% of the acorns of red oaks. 

This Eastern Gray Squirrel is eating the sweeter White Oak acorn and not bothering to bury it for later. Photo by Paul Johnston / CC BY (https://creativecommons.org/licenses/by/3.0).

Gray squirrels bury acorns in different places, which is called scatter hoarding. It is thought that they use both their memory and landmarks to find their caches. When a squirrel grabs an acorn, it often does a quick head flick and turns the nut several times in its paws and mouth. These behaviors help the squirrel determine the nut’s freshness and weight, as lighter acorns are often infested with acorn weevils. But, as we know, squirrels don’t remember where all their acorns are, so we can thank them for planting new trees.

Oaks need our help. Some stands of oaks have been hit hard by invasive species. There have been major Gypsy Moth (Lymantria dispar) infestations in the last few years, particularly in eastern Connecticut. Oak wilt is a vascular plant disease caused by the fungus Bretziella fagacearum. This fungus grows on the outer sapwood and restricts the flow of water and nutrients through the tree. It has infected many oaks in the eastern United States, particularly the red oak group, and has been recently confirmed in eastern New York, including on Long Island. To help control the spread of oak wilt, please don’t move firewood long distances.

If you are thinking of planting a tree, consider planting an oak. Your grandchildren will enjoy its shade and the wildlife around it will flourish. Although oaks take a long time to mature, they have an average growth rate when young. As philosopher and author Matshona Dhliwayo says, “an oak tree is a daily reminder that great things often have small beginnings.”

Published by Jim Sirch

Jim Sirch is the author of Beyond Your Back Door, a weekly blog about nature in your neighborhood. He is also Education Coordinator for the Yale Peabody Museum, a UConn Master Gardener and board member of his local land trust. As a trained naturalist, he brings a deep understanding of geology, plants and wildlife and how they interact within a particular ecosystem. He holds a B.S in Forestry from West Virginia University, a B.S. from Miami University in Science Education; and an M.S. in Environmental Studies Administration from Antioch University. He is also the 2014 Sigmund Abeles Award recipient from the Connecticut Science Teachers and Supervisors Association for outstanding science teaching and professional development.

2 thoughts on “Oaks Are Mighty

  1. Is it true that squirrels will often bite off the germ of the white oak acorn to keep it from germinating while in storage? If so, wouldn’t that also contribute to a bias toward red oaks?


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