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Tuesday, July 9, 2024

Alien or Native? How Much Do We Care?

This picture is worth 1,118 words, or at least that's how many we gave it.

What's wrong with this photo? See below. 

We count a dozen native species in the photo above, but there are also three species here that have been called aliens. Some ecosystem stewards focus on aliens; they want them out! Then, whatever happens, whichever species then flourish, regardless of biodiversity, is nature and good. That's one interesting experiment.

At Somme Prairie Grove our restoration experiment seeks to rise to a different challenge: can we restore nature such that it conserves biodiversity, as close as possible to the richness in once achieved. We start with the understanding that nearly all ecosystems of any size in the tallgrass American heartland are damaged and depleted to some degree. They're losing species and alleles of great potential importance to the future of humanity and the planet. Especially those on rich soils. At Somme we inherited a remnant with about 250 native plant species. Thanks to seed gathered from surviving nearby populations of missing species, we now count nearly 500 native species. And yet there are a few aliens mixed in. The photo above shows mostly thriving rare savanna flora. But those three other species raise questions. 

Zooming in, silhouetted against the big prairie dock leaf is the alien grass Redtop (Agrostis alba or gigantea). Although "apparently native in the northern parts of both the eastern and western hemispheres" - it's considered alien here. Or more precisely, according to Swink & Wilhelm, "Much of the population in the Chicago region apparently does not represent a southern extension of the natural range, but rather consists of elements introduced from Europe?" Is it damaging? Should we consider ways to get rid of it? That would be quite a challenge, and we have more pressing concerns.

We could say the same about a second species here, Kentucky Bluegrass (Poa pratensis). Its wispy dried seed heads are visible here and there, if you look close, for example to the left of the prairie dock leaf, just above the budding early goldenrod. Another circumpolar species, this one "almost certainly" consists of European strains today. "It is actually a serious weed in many situations, but in most instances this weediness is not accurately evaluated," reports the Plants of the Chicago Region (1979). But the subsequent Flora of the Chicago Region by Wilhelm & Rericha (2017) tones down the alarm bells. There seems to be less and less of it at Somme over the years, as fire and more competitive conservatives drive it out.  

But the big conceptual adjustment comes with the third iffy species, Yarrow (Achillea millennium). It's an alien in Swink & Wilhelm but upgraded to native in Wilhelm & Rericha: 

"Many have asserted that Yarrow is introduced from Eurasia, although Higley & Raddin (1891) considered it native and common in their time. Willison (1945) reported the observations of the Pilgrims in 1620 at Plymouth, Massachusetts, who mentioned that Yarrow grew in the area."

Zooming in again, yarrow is the creamy white flat-topped flower on both sides of the lavender wild bergamot (below, right). For years we sort of filtered yarrow out of our consciousness as we studied the ecosystem. What is it about yarrow? We never even considered assaulting it, as we did so many plants labeled alien. It seemed more integral and okay.  Wilhelm & Rericha eased whatever angst we had.

None of these three long-denigrated community members do any apparent damage to the whole. In the early years, our best ecosystem restoration experts and mentors used to tell us: have faith! be happy! the high-quality tallgrass ecosystems, managed properly with fire, will in time drive all the bad guys out. 

They were dramatically wrong about some. At least in comprehensible time frames - when it comes to such malignant killer plants as crown vetch, teasel, and reed canary grass - left unchecked they can destroy a healthy, high-quality ecosystem.

To our surprise, some native malignant plants can do the same. In the absence of fire, fine native maples can shade out and destroy the biodiversity of an oak woodland, oaks and all. In the badly damaged but recovering ecosystems of today, species like native tall goldenrod (Solidago altissima) and woodland sunflower (Helianthus strumosus) can in some situations become so dense as to kill off many or most other native species (including some conservatives of importance to biodiversity). We've never seen bluegrass or redtop do that. What's important is not whether a species is alien or native. It's whether the species can be malignant. 

Whether it's considered alien or not, yarrow doesn't seem to do harm. Perhaps some of its genetics these days include imported European strains. Should that make us feel unclean somehow? 

Our goals and principles tell us no. We do not endeavor to restore ecosystems to exactly what they were in 1491. The urgency is for a different goal. Loss of biodiversity, side by side with climate change, is one of the two major threats to life on planet Earth. We can do something about biodiversity, here, now, with our hands, backs, and minds. We do it. And we're so happy for that privilege.

Comment on the plant composition in the photo

Parts of this area have large amounts of such conservative, important, early-season plants as shooting star, hoary puccoon, bastard toadflax, prairie violet, white blue-eyed grass, dropseed grass, Leiberg's panic grass, Junegrass and so many others.  Such species are "everywhere" in a very high quality prairie or savanna. These are spreading by themselves these days but seemingly hadn't spread into this photo yet. 

We wonder whether there is less Kentucky bluegrass and redtop in the areas where more of those high-conservatives thrive. Perhaps early-season conservatives will largely out-compete the two early-season alien grasses in the area of the photo. Worth some study. But then again, we're busy this time of year "hunter-gathering" seeds and killing crown vetch, teasel and reed canary grass. As we learn more, you'll be the first to know. 

The evidence seems to be that very-high-quality remnant prairies (there are no very-high-quality remnant savannas) also have Bluegrass and Redtop. Are they now "naturalized" here as a minor part of the flora most everywhere? The area of this photo is a former cornfield, later pasture, later under ecological restoration since 1980. Random sampling shows that the whole site including the now-best areas continue to improve in conservative biodiversity, growing season after growing season. 


Written and edited by volunteer stewards Stephen Packard, Eriko Kojima, Rebeccah Hartz, and Christos Economou.

Ultimate credit also goes to the Cook County Forest Preserves for expertise, resources, and protection of this site since the 1930s. 

The Illinois Nature Preserves System, the institution and its staff, has provided Somme Prairie Grove here with additional protection and scientific resources since 2021, and, as is its mission, forever. 


List of species in the photo

If it helps anyone find them, we searched the photo like reading a book, starting top left and reading across a strip covering about the top third of the photo, mentioning only the plants in bloom (color), if any are in bloom. Otherwise we say something about the leaf or whatever. We mention only the first instance of each species. 

Top strip:

Wild bergamot (lavender)

Mountain mint (white)

Early goldenrod (yellow)

Leadplant (purple)

Kentucky bluegrass (in many places but easy to find just left of the prairie dock leaf)

Prairie dock (big green leaf)

Redtop (posting against the prairie dock leaf)

Spiderwort (was blue, but now just some dried flower parts to the right of the tip of the prairie dock leaf)

Middle strip:

Butterfly weed (orange)

Rattlesnake master (white spiky spheres)

Kalm's brome grass (brownish maturing seeds, hanging down)

Heath aster (won't bloom until fall; it's all over this photo ... but most obvious as clusters of tiny heath-like leaves under the Kalm's brome)

Bottom strip:

Big bluestem grass (green and ranging all over) (probably some of the finer leaves are dropseed grass, of which there's a lot in the area, but none is easy to distinguish in the photo).

Yarrow (creamy white)


Our apologies to the beetles and other little invertebrates visible in the photo here are there. Equally important to the ecosystem, but they need different expertise than we have.

Savanna birds regularly seen or singing in the area of this photo include orchard oriole, eastern kingbird, field sparrow, indigo bunting, yellowthroat, song sparrow, cedar waxwing, and others.

Fourteen companion photos from the same place on the same day

Including some animals and comments, a lot more companion plants, and the first sneak peak at the photo that's subject of this post, click  here


  1. A thought provoking post.

    I remove bluegrass from prairie gardens. It does not compete well with native plants. In a native plant garden bluegrass roots are limited to less than an inch of soil above the native plant roots. A dandelion weeder will easily get under the root so a clump of bluegrass can be lifted out of the soil and removed.

    Targeting bluegrass would not make sense in a prairie restoration or reconstruction. The trampling that would have to be done to remove all the bluegrass would be counter productive. However, when I patrol for other weeds I will remove blue grass or Canada bluegrass opportunistically.

    It is not that removing bluegrass from prairie restorations or reconstructions is undesirable. It is a matter or priorities. With limited resources, people tend to focus on the biggest problems and leave minor problems unattended.

  2. Wise post! I've been thinking about this a lot lately. Thank you.

  3. Morton arboretum researchers observed ants bringing Kentucky bluegrass seed into prairie remnants. The cool season grass may have an effect on fire dynamics. On the other hand cool season grasses are nesting material for grassland birds. Peregrines eat city pigeons. What to make of species moving their range into our area that in pre-settlement times had a more southern range? At the end of the day we want to keep genetic diversity alive and hope LIFE has more days ahead of it than behind it.

  4. Somme Prairie Grove is a very nice site with great and increasing plant species diversity. That said, it is not because you have ignored managing Agrostis gigantea and Poa pratensis. Those grasses are essentially impossible to reduce in abundance by stewards (because there are many and hard to identify leaves plus rhizomatous growth) without extensive collateral damage to nearby species. Hopefully the native species will do the ‘the job’, as you say. Why criticize/abandon a goal when practical issues do not allow it to be achieved?

    Nature is dynamic. Species move around. Our area was under ice for many years and has only been recolonized in the last 10,000 years. Taxonomy is also dynamic. Species can be split and merged, so there will be questions about the nativity of species at a place, but proportion of species with debatable nativity will be less than 10%. As you do, I see impact on the other species in the community more important than what a book(s) says. But most plant species are either clearly native or imported by people for agriculture and gardens.

    This post would have been more interesting to me if the species in the image had been more potentially controllable. I suggest 1) burdock, (exotic, big local impact, but rarely spreading extensively in a natural community, moderately difficult to control), 2) Queen Anne's lace (exotic, small impact, effectively spreading but not dominating, easy to control by pulling), 3) sweet clover (exotic, big impact, dominating, control by pulling not always effective), 4) a small grey dogwood (native, little current impact but potentially dominating, tedious to control). If any of those four species were in the image, would the same, ‘don’t worry about aliens, focus on biodiversity’ write up the grasses got have been given?

    For each species potentially being managed (to reduce its abundance) I find it useful to think about and categorize 1) the methods and effort required to significantly reduce that species’ abundance, 2) potential damage to abundance of desired species of the method(s), and 3) the impact on the desired species of the ‘do nothing’ option (how effective is the managed species in displacing native species (within a 2-5 year time frame). Obviously species with great potential impact, easiest to control with methods generating least damage to native community are an easy first choice, but current impact and time needed is also important.

    This post talks about a biodiversity goal and also about conservative plant species. I agree that Somme Prairie Grove has achieved such a goal which I measure subjectively from my experience. Do you like a more quantitative measure, ie number of native species, average C value, number of 9 & 10 C species?