Why Keep the Aliens Out ?

wordsworth-lonely-daffodils1-500x334       Caterpillar on dogwood

I have nothing against daffodils, really.  They did, after all, inspire Wordsworth to write one of the best-known poems in the English canon. He and the other 19th century Romantics reminded us of the tremendous spiritual potential of nature. We need that more than ever these days to inspire us to reverse all those unintended consequences of population growth and the industrial revolution.  And I know it’s risky to quibble with one of Romanticism’s best beloved poets.


The narcissi are lovely, I admit, and the fragrances  of some varieties put Chanel’s commercial concoctions to shame..  But all those daffodils popping up in suburban gardens as winter gives way to spring give me pause.


Like starlings, purple loosestrife, dandelions, English Sparrows, house mice and Norway rats, daffodils are aliens – one of so many species native to elsewhere and brought to this hemisphere by us either as stowaways or intentionally for one reason or another.  (The American Acclimatization Society brought  European Starlings and English Sparrows as part of a campaign to introduce all the birds mentioned by Shakespeare into the New World!  Fortunately the plan expired soon after it was hatched.)  Most alien birds and mammals thrive in man-made environments:  house eves, under bridges, near dumpsters.  Alien plants typically thrive because they have no natural “enemies” in their non-native habitat.  I put “enemies” in quotes because both the native species and the herbivorous critters that munch them are part of an ecological balancing act which keeps them both in check.  But the aliens exist outside the equipoise.


Chipmunks, squirrels and moles won’t molest a daffodil bulb. Deer leave the leaves alone.  In England there are narcissus flies both large (Merodon equestris) and small (Eumerus spp) but there are none in this country and daffodil flowers and foliage in the U.S. rarely look motheaten.   Alien species typically thrive in their non-native environment precisely because they are not part of an established ecosystem and have leapfrogged coevolving herbivorous critters designing digestive systems able to make use of their flesh.  Given tolerable growing conditions, aliens thrive unmolested – and their flowers and foliage look pristine.   That is great news for the gardener but it turns out to be pretty bad news for birds.


Douglas Tallamay, Professor & Chair of Entomology and Wildlife Ecology at the University of Delaware,  studies the biodiversity associated with alien versus native plants and finds that, typically, native plants support 29 times the biodiversity that aliens do.  That’s not 29 percent more.  That’s 29 times or 2900 percent more!  It makes sense once you think of it.  If you were a bug in an arms race with a plant that was gradually evolving chemical defenses to poison you (as is what happens in nature, after all) wouldn’t you in all likelihood gradually evolve biologic detoxifying systems to neutralize the poisons which that otherwise tasty native plant is producing?  


Of course you would, but that takes time – a lot more time than it takes to ship a bunch of plants from one continent to another.  So fine gardens end up being filled with a bunch of plants that “pests”  ignore.  But those “pests” just happen to be sustenance for lots of other species.   In his book, Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, Tallamay notes that in the 16 days between hatching and fledging, a clutch of Carolina chickadees requires 9000 caterpillars from their parents. Studies of native oak trees have shown that they, on average, support 530 different species of caterpillars and butterflies.  Non-native ginko trees (Ginko biloba), on the other hand, support only three.  Ginko’s, of course, are just an example of the generic problem.  Kousa dogwood (Cornus kousa) supports no native herbivorous insects.   Our native flowering dogwood (Cornus florida), on the other hand supports 117 species of moths and butterflies.  If all there are in your neighborhood are blemish free ginko and kousa dogwood trees replacing all those tasty natives, where are the chickadees going to go to get enough supper for their chicks?   The fact is that a yard full of non-native species will be less biodiverse, its soundscape impoverished of birdsongs, and fewer butterflies will float around the weeding gardener.  Unfortunately, what isn’t there is easy to overlook.


In the spirit of full disclosure, I have to admit that I have daffodils popping up all over my yard.  And a while ago I planted a kousa dogwood.  But that was before I knew about Profesor Tallamay’s interesting findings.  Now when I go to a nursery, I at least ask the proprietor whether or not the plant I’m considering is a native – just like I ask my fishmonger about the origins of that good-looking salmon fillet.


So, with apologies to Mr. Wordsworth, may I suggest that had he lived in this country instead of England he might have begun his famous poem this way:


I wandered lonely as a cloud

That floats on high o’er oaks and pine,

When all  at once I saw a crowd,

A host. Of native columbine

Beside the lake, beneath the trees,

Fluttering and dancing in the breeze.


3 thoughts on “Why Keep the Aliens Out ?

  1. “Unfortunately, what isn’t there is easy to overlook.” So true, and such a sad truth. Thank you for the thoughtful post.

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