Colorado Native Oaks, Again!

| Colorado Native Plants, Ecological Services, Native Landscape Planning & Design

By Deb Lebow Aal

Quercus gambelii, Gambel Oak.

I have written an article on Gambel Oaks, and another article on why all native plants are not equal. This article combines the two, and coins the term super native plants! Oak trees are super native plants, as anyone who listened to Doug Tallamy’s talk on oaks last month knows.

Doug’s talk went through a year in an oak tree’s life. It was, of course, an east coast oak, and perhaps not everything he said is relevant to our native western oaks, but much of it is. So, first, a bit about Gambel Oaks, or scrub oaks, and why they are a super native. And then we’ll delve into some nuggets from Doug’s talk that I think we all need to know.

A super native plant is one that supports an extraordinary number of insects. There are native plants that you may like and are beautiful, but support very few species of caterpillars and moths. For example, if you look on the National Wildlife Federation’s native plant finder, in my zip code, I can plant Monarda (Bee balm), a beautiful plant native to my local ecosystem, but it only supports seven species of caterpillars and moths. Seven is better than none, but if I plant one Gambel oak, it will support 221 species of caterpillars and moths. That makes it a super native.1

Gambel oaks used to be common along Colorado’s Front Range, but are now threatened due to development. In many areas, they are not appreciated as they do spread and do their own thing. But a recent study (discussed in the article referenced above on Gambel oaks) found 124 species of arthropods (insects, spiders, etc.) representing 57 families on 10 insect orders. That suggests that Gambel oaks play an inordinately important role in the local ecosystem. As insect populations have plummeted in recent years, and as insects are SO important as an anchor to the local food web, it behooves us to plant some Gambel oaks. That’s my plea.

If that isn’t enough for you, our state insect, the Colorado Hairstreak (Hypaurotis chrysalis) develops on Gambel oaks. Gorgeous butterfly on a gorgeous tree. Granted, that’s my opinion, but if you find Gambel oaks unruly, you really can prune them to be lovely specimens. The Denver Botanic Garden has quite a few fully grown you can go and see.

Here is some additional information on oaks, and on trees in general, From Doug’s presentation.

First, in its first year, an oak grows more than 10 times more root mass than leaf mass. So, if you think your oak tree is growing too slowly, it is, but only above ground. Most of its growth is not visible in the first few years. Only once it has sufficient root mass, does it start visibly growing above ground.

Quercus gambelii at DBG,
with Liz Evans
American Plum, a Colorado native tree.
And another super native plant, American Plum (Prunus americana)
The Colorado Hairstreak butterfly on a Gambel oak.
Colorado Hairstreak Butterfly

Second, Doug suggests we buy our trees small. When you buy a big tree in a pot, it is most likely root bound, and doesn’t have enough root mass to support the tree. Same with a bare-root large tree. So, as these bigger trees expend their energy building uproot mass, smaller trees will catch up to the bigger trees in no time, and are stronger in the long run. Smaller trees are of course cheaper to buy, too.

Third, oaks keep their leaves through most of the winter, shedding them toward spring. Most of us know this if we are paying attention on our walks, but keep that in mind in your placement of an oak tree. You don’t want to plant the oak where it will block light or warmth in the winter. And you can use this deciduous tree almost like an evergreen, as a screen.

Fourth, you don’t need a big oak tree to support the ecosystem. Your tree will start supporting caterpillars, moths, and other insects as a small tree, immediately! If you want, you can keep your oak tree small, coppicing2 every few years.

Fifth, You never (NEVER!) have to fertilize your tree if you leave the leaf litter there. Leaves as they break down under the tree return the nutrients to the tree. And of course we all know by now that we should leave the leaves anyway, as they support a myriad of life as they decompose.

And, finally, trees like to be close enough to touch roots. Think about putting groves of trees in, instead of specimen trees, like we see in parks (and really, everywhere). They are much more stable when growing in groves, rather than as one offs.So, think about a place in your landscape where you can put a Gambel oak. Better yet, think about where you can handle a grove of oaks. Remember the old adage – the best time to plant a tree was 20 years ago, so do it now.

Also from Doug’s presentation, as we think about using our landscapes to make the ecosystem better, here are four things you should think about. Your landscape should:

  • Capture carbon;
  • Help manage the watershed;
  • Support a diverse community of pollinators; and
  • Support a complex food web.

It turns out oaks do all four of these. As I said last month, your landscape can contribute to an ecosystem that is supporting your local food web, or it can do nothing for, or even detract from, the ecosystem. There is so much more in Doug’s presentation, I urge you to watch the whole thing, if you haven’t see it. Or, watch it again!

Curious to learn more about transforming your garden into a habitat with Colorado native wildflowers, grasses, shrubs, and trees? Check out our native gardening toolkit, register for an upcoming event, subscribe to our newsletter, and/or become a member – if you’re not one already!

Close-up of chocolate flower, a Colorado native plant.
Chocolate flower (Berlandia lyrata) is a beautiful native plant, but it is not a super native!
  1. More super natives in my zip code are: Willow (Salix): supports 322 species of caterpillars and moths (But beware – first, this is not the only metric for an ecologically great plant, and second, willows like lots of water!); Aspens, Cottonwoods and Poplars: 262; Beach, plums, choke cherry (Prunus): 261; Maple (Acer): 140; Rose (Rosa woodsii): 91. More plants I would not consider super natives: Sage (Salvia): 9; Globmallow (Sphaeralcia): 8; Blazing star (Liatris): 6; Spiderwort (Tradescantia): 1; Tansy (Tanecetum): 1. But remember, one is better than none! ↩︎
  2. Coppicing is a traditional method of woodland management which exploits the capacity of many species of trees to put out new shoots from their stump or roots if cut down. In a coppiced wood, which is called a copse, young tree stems are repeatedly cut down to near ground level, resulting in a stool. ↩︎