Becoming Part of Homegrown National Park

I've always liked native plants--stately cottonwoods (Populus deltoides), dramatic redbuds (Cercis canadensis), robin-attracting serviceberry (Amelanchier alnifolia), blanketflowers (Gaillardia species), columbines (Aquilegia species)...I can go on and on. I grow them in my yard (well, not the cottonwood, too big) because I like them. But I also have a bit of Kentucky bluegrass lawn (Poa pretense, from Eurasia), creeping buttercup as a ground cover (Ranunculus repens, from Europe), a maple (Acer, not local to area), lilacs (Syringa vulgaris, from Eurasia), iris (Iris, from all over the world), peonies (Paeonia from China), crocus (Crocus from Eurasia) and many others. I like them too.

blanket flower, Gaillardia, native

What I learned recently is that native animals--butterflies and moths, but also wood-borers and leafhoppers--often cannot eat introduced plants. That makes sense to me. In fact, I used to teach that one of the reasons for species being invasive is that they left behind the animals, fungi, and bacteria that ate them, and, with very little damage in the new continent, could grow much better. I never thought about the reverse of that: the impact of nonnatives on the native food chain.

lilacs, Syringa vulgaris, nonnative

columbine, Aquilegia coerula, native

The food chain begins with plants. Insects eat some part of the plant. Birds, frogs, and other small vertebrates eat the insects. Bigger predators like hawks and foxes eat those. If the insects can't eat the plants, not only do they die, but every animal up the food chain goes hungry. 

Recent study (see references below) documented that bird numbers in North America have dropped 30% (almost 3 billion birds!) since 1970. A big part of that is development: roads, houses, shopping malls, and parking lots that have few or no plants to produce insects compared to the forest or grassland that was there before. We think our environment is green because we put plants around our houses, but the bluegrass lawn is an exotic insect-poor monoculture and the peonies, lilacs, and creeping buttercup are exotics native insects can't eat. Biologists working on this problem have documented that few native insects eat non-native plants because plants defend themselves with unique poisons, so animals have to specialize to detoxify the poisons, which ends up with them eating just one or a few plants. Alas, they can rarely overcome the defenses of alien plants. And, if insects aren't eating, and creating more insects, there is no food for birds. We are seeing the consequences.

peonies, Paeonia species, nonnative

The solution, coming from Douglas Tallamy and others, is Homegrown National Park (link). That is, we don't leave it to someone else to provide the plants at the bottom of North American food chains, but we all pitch in. If each of us grows a few natives in our yards, it adds up to a massive resource for native animals. For the most part our birds aren't extinct and will rebound in numbers if conditions improve. 

creeping holly grape, Berberis repens, native

That's a compelling reason to grow native plants, particularly plants native to your immediate area, not just North America. I am convinced by the logic (see Tallamy's writings in the references for more detail). But...my yard is easily 80% nonnatives. I could swap out a LOT of plants to be more of a supporter of Homegrown National Park. And, as always the devil is in the details. I'm thinking hard about how to shift to a yard that has more natives than exotics (a humble goal, really) and will write about some of the issues in the future. 

creeping buttercup, Ranunculus repens,  nonnative
a pest east of us, but a nice ground cover in Colorado

But yes, I am shifting my yard and garden goals to include contributing to a richer environment for birds (and butterflies and dragonflies and all the rest!) 

Comments and corrections welcome.

References

Axelson, S. 2019. Vanishing: More Than 1 in 4 Birds Has Disappeard in the Last 50 Years. Living Bird. Autumn  2019. link Accessed 3/25/22.

Cornell Laboratory of Ornithology. Nearly 3 Billion Birds Gone. link Accessed 3/25/22. Includes link to pdf of the Science paper that reported this. (also listed below on Science's website).

LearnBirdWatching.org Do Birds Eat Caterpillars? The Answer Might Surprise You. link (Accessed 3/25/22).

Renault, M. 2020. An Ode to Nature's Hotdogs: Moth Caterpillars. Audubon. link

Rosenberg, K. V., A. M. Dokter, P. J. Blancher, J. R. Sauer, A. C. Smith, P. A. Smith, J. C. Stanton, A. Panjabi, L. Helft, M. Parr, P. P. Marra. 2019. Decline of North American Avifauna. Science 366: 120-124. link

Tallamy, D. W. 2017. Bringing Nature Home. Timber Press. Portland, Oregon.

Tallamy, D. W.  2020. Nature's Best Hope. Timber Press. Portland, Oregon.

Tallamy, D. W. webpage: link

Tallamy, speaking to the meeting Landscaping with Natives in Northern Colorado on 2/28/22 had impressive graphs of the % of the diet of nestlings that were caterpillars (70% for bird species after bird species). I cannot find a reference, so that may not have been published yet, but only gathered from the scattered literature. The Learn Bird Watching article has a list of common birds that eat caterpillars (though without references) and a lot about why. 

Kathy Keeler, A Wandering Botanist
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