Oaks are essential to creatures, too – The Virginian-Pilot

Oak trees have always been a favorite tree for gardening enthusiasts and non-gardeners alike. Whether oak trees are found in a peaceful landscape, in a city park, or in your neighborhood, it’s hard not to marvel at their majestic presence. Its large size, shape, and rich colors make it an aesthetically attractive tree in any landscape.

But it is much more than just a beautiful tree. Oaks (Quercus species) are one of the most important trees for our ecosystem as a whole and are what are known as a keystone species: many other species depend on them for survival.

Think beyond squirrels and their nuts.

One of the most overlooked groups of species that depend on oak trees are moths and butterflies (order Lepidoptera). This may seem like an odd group to focus on, but these insects are essential to the life cycle of a healthy ecosystem.

First, how important acorns are to them: many Lepidopterans have a specific plant they evolved with, and it is often the only food source their larvae eat. These plants are known as host plants, and oaks are the host plants for several hundred species of Lepidoptera. This is why oak trees are such an important foundation species: no other tree comes close to providing this level of nutritional support. For context, one of our other great native hardwoods, the tulip poplar (Liriodendron tulipifera), is host to only about 20 Lepidoptera.

Why are moths and butterflies crucial? While the image of thousands of caterpillars from hundreds of species of butterflies and moths feeding on oak trees each year may not inspire you to plant an oak tree, what those caterpillars and acorns do is fascinating. With each bite, the caterpillars convert the chemical energy stored by photosynthesis in oak leaves into nutrients and sugars that the caterpillars can use to continue their life cycle. A huge amount of thermal energy has been transferred into the growing larvae.

Not all of those caterpillars will be able to turn into beautiful butterflies or moths. A large percentage of it will become bird food, since many of our native bird species require thousands and thousands of caterpillars to raise just one set of chicks. The numbers at this stage start to be staggering: thousands of adult birds, each needing thousands of fry for each chick they raise, each year.

How are there enough caterpillars to tolerate this? This is only possible because the acorn is a huge buffet for hundreds of Lepidoptera species and because with enough food, butterflies and moths can produce an incredible number of offspring.

At this point, the oak tree has done an amazing job of transferring an enormous amount of energy into the ecosystem, energy that will continue to rise through the food chain, from prey to predator, until it reaches the top. (And that’s only with caterpillars. Acorns are a vital source of calories for many woodland creatures, including deer, squirrels, turkeys, raccoons, opossums, and foxes.)

Oak trees are unparalleled at converting sunlight into heat energy and injecting it into the ecosystem. It would take dozens of other tree species to accomplish what a single mature oak tree can do for the environment.

So, next time you’re sitting in the relaxing shade of a beautiful oak tree, you can thank it for doing the heavy lifting of preserving the ecosystem that surrounds you.

Wild Green Yonder is a recurring monthly feature presented by the staff of the Norfolk Botanic Garden, where Carl Simons is curator of woody plants. If you have any questions, please send them to askaplantquestion@nbgs.org.