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333-Why Oaks Are Our Most Essential Native Tree, with Doug Tallamy-Encore Presentation

| Care, Podcast

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

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

 

Oak leaves

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.

 

treehopper

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. 

 

Prothonotary warbler

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

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GGW Episode 509: Greening of Suburbia

GGW Episode 1008: Bringing Nature Home

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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

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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.

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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