Oaks are our most essential native tree, according to entomologist Doug Tallamy, Ph.D. Because so many species rely on oaks for their survival, they’re considered keystone plants due to the pivotal role they play in the food chain.
Doug is a professor at the University of Delaware in the Department of Entomology and Wildlife Ecology. He studies the interactions between plants and insects, and what’s eating those insects. His latest book is “The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees, and his earlier works on the importance of conservation and native ecology include “Nature’s Best Hope” and “Bringing Nature Home.”
Doug Tallamy is a renowned entomologist and advocate for native gardening. (photo: Courtesy of Doug Tallamy)
“Nature is not optional for humans,” Doug says. “We’re products of nature. We’re totally dependent on it. And insects are such a crucial part of the natural world that they’re essential. We can’t lose them.”
Doug wants people to learn that an oak is more than just a tree that drops leaves that they have to pick up — it is an entire community of living things that changes throughout the year. He wrote “The Nature of Oaks” to provide a roadmap of what’s happening on and in an oak any time of year.
For a full recap of my conversation with Doug, see the show notes from the original airing.
Oaks Are Diverse, Productive and in Need of Conservation
There are 435 species of oaks worldwide, all belonging to the Quercus genus, and 91 of them are found in the United States. Quercus provides food for more caterpillar species than any other genus of plants in North America — not to mention all the animals that eat the acorns that grow on oaks. That’s why he calls oaks keystone plants. If you take oaks out of the local food web, the food web collapses.
Doug’s research has found that oaks are the most productive trees in 84 percent of the counties in North America when it comes to producing food. He points out that of the insects that eat plants, 90% can only eat a few plant lineages — the plants that they co-evolved with and have specialized on.
There are 50% fewer oaks in eastern forests than there were 100 years ago. Logging and land clearing contribute to oak loss in addition to oak diseases, such as sudden oak death syndrome, bacterial leaf scorch and oak wilt. The Morton Arboretum in Illinois studied native U.S. oaks and found 28 of the 91 species are of conservation concern.
Of the 435 species of oaks worldwide, 91 are found in the United States. (photo: Courtesy of Doug Tallamy)
Why Oaks Are a Meal for Many Insects
One hypothesis to explain how oaks became so valuable to the food web concerns their chemical defenses. While other plants produce toxins or bitter compounds to make plants unappetizing, oaks only produce tannins. Tannins slow the absorption of proteins, which is a defense that’s much easier for insects to adapt to, Doug says.
Another hypothesis is that oaks have been around for so long that insects have had more time to adapt to them. Individual oaks are large and can live for several hundred years, which gives insects a lot of time to adapt.
Every plant lineage is protecting itself with a unique cocktail of chemical defenses. An insect species can’t adapt to all of those defenses, so it gets really good at circumventing the defenses of a small group of plants, Doug explains.
One example is the monarch butterfly, which can tolerate the cardiac glycosides and latex sap in milkweed plants. If there is no milkweed around for monarch butterflies to lay their eggs on, they will have no place at all to lay their eggs. They can’t just lay eggs on oaks instead, because monarch caterpillars haven’t evolved a way around the oaks’ defenses.
“Caterpillars transfer more energy from plants to other animals than any other type of creature,” Doug notes. When caterpillars don’t have native plants to eat, there won’t be caterpillars around to provide that energy to birds and other wildlife. A landscape without caterpillars is a dead-end for the food web.
Oak treehoppers, Platycotis vitata, specialize on oaks. (photo: Courtesy of Doug Tallamy)
Birds and Insects in Decline
A 2019 Cornell Lab or Ornithology study found that there are 3 billion fewer birds in North America than there were 50 years ago. In 2018, The New York Times wrote the headline “The Insect Apocalypse Is Here.” And back in 1987, naturalist and writer E.O. Wilson penned “The Little Things that Run the World” on the importance of the conservation of invertebrates and what it would mean if the world lost its insects.
Losing insects would mean losing most pollinators of flowering plants. Losing flowering plants would mean losing most of the energy that drives the food webs that support our animals — amphibians, reptiles, mammals, birds and many freshwater fish would disappear. Additionally, the loss of insect decomposers that recycle nutrients quickly would mean organic material would only break down slowly by bacteria and fungi.
These are the kinds of changes that humans wouldn’t survive, Doug says, comparing global insect decline to losing oxygen.
Birds need insects to rear their young, and caterpillars are especially nutritious. Oak trees support numerous moth species, so more oaks equals more caterpillars and, in turn, more birds. (photo: Doug Tallamy)
If you haven’t listened yet to my conversation with Doug Tallamy on why oaks are keystone plants, you can listen to this episode now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you have a keystone plant on your property? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 012: Beneficial Garden Insects – Bringing Nature Home with Doug Tallamy
Episode 050: Organic Pest Control: Beneficial Insects and Beyond
Episode 067: Predatory Beneficial Insects: Feared Foes of Garden Pests, Pt. 1
Episode 071: Gardening for Wildlife: How-to Create an Inviting Habitat, with NWF’s David Mizijewski
Episode 076: How to Create a Bird-friendly Yard
Episode 077: The Beauty and Importance of Native Plants: The Ethos of Mt. Cuba Center
Episode 133: Native Plant Design in a Post-Wild World, with Thomas Rainer
Episode 134: Bird Population Decline and What Gardeners Can Do to Help
Episode 142: Why Our Plant Choices Matter: Nature’s Best Hope, with Doug Tallamy
Episode 152: The Native Plant Trust: Why Plant Choices Matter
Episode 184: More Must-Have Books for Every Gardener
Episode 197: The Many Benefits of Building a Naturalistic Garden, with Kelly Norris
Episode 237: Ecological Gardening: Creating Beauty & Biodiversity
Episode 258: Averting the Insect Apocalypse, with Dave Goulson
Episode 262: Garden for Wildlife: Accessing the Right Native Plants, with the NWF
Episode 303: We Are the ARK: Acts of Restorative Kindness, with Mary Reynolds
Episode 331: The Ecological Garden Blueprint: 10 Essential Steps That Matter Most
joegardener blog: Why to Leave the Leaves
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course. The course is designed to be a comprehensive guide to starting, growing, nurturing and harvesting your favorite vegetables: no matter what you love to eat, no matter where you live, no matter your level of gardening experience.
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Earthbound Expeditions: Discover South Africa with Joe Lamp’l
GGW Episode 509: Greening of Suburbia
GGW Episode 1008: Bringing Nature Home
“The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees” by Douglas W. Tallamy
“Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard” by Douglas W. Tallamy
“Bringing Nature Home: How You Can Sustain Wildlife with Native Plants” by Douglas W. Tallamy
Cornell Lab of Ornithology Study: Nearly 3 Billion Birds Gone
“The Insect Apocalypse Is Here” from The New York Times
“The Little Things that Run the World” by E.O. Wilson
Morton Arboretum: Conservation Gap Analysis of Native US Oaks
Greenhouse Megastore – Our podcast episode sponsor and Brand Partner of joegardener.com – Enter code JG10 for 10% off your order
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast was based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Corona Tools, Milorganite, Soil3, Greenhouse Megastore, Territorial Seed Company, Earth’s Ally, Proven Winners ColorChoice and Dramm. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
