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Friday, February 2, 2024

Rare Grass vs the Leave-It-Alone Hypothesis

It was growing in the wrong county and the wrong habitat, at least according to the current books.

But tell that to the grass!

And rare? It's certainly rare in the region and habitat where we found it. Wilhelm and Rericha (2017) show it absent from Cook County and all counties north and west. They do show it in all counties to the south and east of Cook - but growing on sand. At Somme Woods, it suddenly turned up under interesting circumstances in rich woodland.

The name of the plant is deer-tongue grass (Panicum or Dichanthelium clandestinum). Wilhelm and Rericha give its habitats as sandy "wet to dry habitats, often in thickets." Their associated species lists cover just two sandy habitats "wet-mesic to mesic woodlands in the dunes region" and "dry-mesic to dry sand prairies."

Unusual for a grass, this species has wide horizontal leaves. Unlike the similar wide-leaved panic grass, the leaf-sheaths of deer-tongue grass are furry, 

The experts are usually right, but not always. And conditions have changed. Older books often have very different reports on where species were found back then. For example, H.S. Pepoon's Flora of the Chicago Region (1927) reported that deer-tongue grass in "woods north and west" (of Chicago) - like where Somme Woods is. He characterized this species as "frequent." 

Many plant species that were once more widespread survive today in some of their former habitats but not in others. One striking example of that emerged from a kind-of-bold experiment by steward Barbara Turner. Her woodland had long been in Turner's family, and she continued to manage it when it was dedicated as Reed-Turner Woodland Nature Preserve in 1980. Until that time no Nature Preserve woodland had ever been recognized as needing fire. Barbara, a careful observer and former student of May Theilgaard Watts, was concerned that some of the rare species (including pale vetchling, on the Illinois Endangered list) seemed to have faded out nearly everywhere. Advisors recommended a burn and, indeed, she received the first ever permit to burn a Nature Preserve woods. That burn had dramatically positive results, but no pale vetchlings emerged. For many species, when they're gone, they're gone.

Barbara's lawn and house were adjacent to the preserve. One day she said, "We call it a lawn. But it's just more woods that happens to have been mowed occasionally. What if we stop mowing?" Indeed, as she stopped mowing and started burning, up popped the pale vetchling as well as another plant, then unknown in Lake County, violet bush clover. (We later found that clover growing nearby with rich savanna associates along the edge of a railroad right-of-way.) These species had survived in the area where mowing kept it sunny - but not the shade of the brush that had build up in the "preserve." Shade kills. And there's little "seed bank" from most species in woodlands. 

Back to deer-tongue grass - at Somme Woods there was a "picnic grove" that had been mowed since the Forest Preserves purchased this land in the 1930s. The mowed area had widely spaced old white and bur oaks, like the adjoining preserve. About two decades ago, steward Linda Masters suggested a switch from mowing that area to restoration and burning. When the mowing stopped, the North Branch woodland seed mix was broadcast there.  

But we didn't then just leave it be. We occasionally selectively scythed tall goldenrod from the area, as that seems sometimes to facilitate the establishment of a desirable conservative turf. And additionally, a couple of years ago we noticed that, from the adjacent never-mowed edge, woodland sunflower seemed to be invading and shading out the otherwise increasingly rich, restored vegetation. So, as we sometimes do, to see if it would help, we started selectively scything that dense sunflower too. Happily, when we did it, we noticed what seemed like a familiar quality plant we hadn't seen here before, wide-leaved panic grass, reaching unusually high toward the sun, in the shade of the woodland sunflower.   

But one day as we passed by in 2023, it just looked seriously wrong. We studied it. It was deer-tongue grass, a species none of us had ever seen. When we looked more carefully, we found another plant of that same species, about 20 feet away, also on the scythed edge between the mowed lawn and the "preserved" woods. We wonder if we would ever have seen it if we hadn't scythed but "just left the place alone." 

But now the question became: how could these plants have gotten there? Was this an example of the Barbara Turner experience, where a species had survived where occasional mowing kept aggressive competitors at bay? Perhaps its partly-mowed stems survived in the brighter sunlight, but the species was lost from the community where the un-mowed woods had grown increasingly dense? Or had it arrived on someone's shoe, or the wheels of a mower, years ago? For a variety of reasons, all three seemed unlikely. But there it was. 

So the questions became: what to think about it, and what to do about it? Should this species just be left alone because we are unsure what to do? Should it be pulled out as a possible invader? Should deer-tongue grass seed be harvested and spread, because that added diversity would restore integrity and benefit the woodland ecosystem restoration? Is this a recovered, nearly lost species here? Or is it somehow spreading north because of global warming? And if seeds of this species go into the Somme seed mixes, should it then be another species shared among all the North Branch Restoration Project seed mixes? 

The Somme Woods work was conceived by its original Forest Preserve staff and volunteers as what has seemed to many to be a noble experiment. The goal here has been much like the Somme Prairie Grove experiment, that is, restore all species that would likely have been there, and let them work it out, after a period of providing biodiversity with various kinds of help for at least the short term. Does deer-tongue grass fit into that vision? For now, we're just watching it to see how it behaves. 

But how should we think about a plant like this? 


Here, the deer-tongue grass in the foreground is joined by diverse other species including three in flower:  nodding wild onion (pinkish white), elm-leaved goldenrod (yellow), and woodland Joe Pye weed (pale purple).  

The upper part of this photo gives a better sense of how dense the now-scythed vegetation had been becoming. The somewhat aggressive species include tall goldenrod, woodland sunflower, woodland Joe Pye weed, and tall coreopsis. 

Deer-tongue panic grass is on the left. Wide-leaved panic grass is on the right.
Notice that the sheathes (that cover the stems beneath the leaves) are furry in deer-tongue and smooth in wide-leaved. These grasses are shown here side by side for comparison, but typically, with us, the deer-tongue is taller and more erect, and wide-leaved is more spreading. 

A person could argue that deer-tongue grass shouldn't get special care because, at C = 4, it is less conservative than many of the species increasing here, including wide-leaved panic grass at C = 8. Someone else might argue that diversity is key, including the full range of species of the natural ecosystem from C = 0 to C = 10.  


Thanks for comments and suggestions to Becky Collings, Christos Economou, and Eriko Kojima.


  1. Plants don't read field guides or observe county lines.

  2. Probably a expanding range but study the biogeography of this species. It is certainly a "good" no native grass species and belongs in regional (just south of Chicago) woodlands... So it is pretty easy to see it at home under the mower in forest preserve edges, etc.

  3. I have it on a south facing solid clay hill prairie in Porter County IN

    1. Clay can create a habitat much like sand even though they are very different. Sand has large particles that allow water to drain away. Clay has particles that are so small that water is not absorbed quickly and tends to runoff. These properties both can create a habitat that is very dry.

      Sand or clay can be alkaline or acidic. Oak trees drop leaves with a lot of tannins that are acidic. It is possible a species typical of more acidic habitats is growing at Somme Woods because of all the oak trees. Another possibility is the oak trees grow there because the clay is more acidic.

    2. On oak knoll woodland remnants on fine textured soil over dolomitic glacial tail--blueberries and huckleberries grow. But not where cattle have ever grazed. Buckthorn also increases soil pH and is concurrently more abundant where cattle grazed (almost everywhere).

    3. I must wonder if the blueberries and huckleberries are growing on the decaying remains of old oak tree trunks. Wood itself is not acidic. It does not acidify soil as it decomposes (if aerobic). However, rain is acidic with a pH of about 5.5. Wood lying on top of the soil can create an acidic habitat due to the pH of rain until the decomposition of the wood has been completed. For the trunk of large oak trees, this could take a long time. Decomposing tree trunks could be causing diversity in the ecosystem by creating substrate heterogeneity.

      Alternatively, after thousands of years rain could have leached calcium carbonate out of the glacial till on ridge tops making them acidic.

      Possibly, both situations could be important for allowing acid soil loving plants to grow where there is calcareous glacial till.

    4. I was wrong before about wood not being acidic. The tannins in wood make it acidic just like with oak tree leaves. This is how wood can be more acidic than rain. A pH lower than that of rain (5.5) is the preferred habitat for plants like blueberries (pH 4). The pH of wood changes over time as it decays. Once a log has fully decomposed, what is left are the minerals which would increase soil pH. This would be the equivalent of a fire burning a log completely to ashes.

      Large logs take a long time to decay. The presence of decaying logs could still be what allows blueberries and huckleberries to grow over calcareous till. The part about diversity being due to substrate heterogeneity is still possibly true. Although, it would take a long-term study to prove.

    5. Below is a reference to a research paper that provides the pH changes in wood as it decomposes.

      "Wood decomposition, carbon, nitrogen, and pH values in logs of 8 tree species 14 and 15 years after a catastrophic windthrow in a mesic broad-leaved forest in the East European plain", Forest Ecology and Management, 2023, Vol. 545, Article 121275

      In my garden, wood chips do not change soil pH much if they change it at all. The differences in where measurements are taken, decomposing logs versus the soil, and the change in the pH of wood as it decomposes probably are reasons why there is so much conflicting information on the subject.

      Also, the preferred pH of blueberries is 4.5 rather than 4. I knew this fact. I should have double checked and given a more accurate number before including it in my comment.

  4. This is very interesting. My brother Tom thought he found this species in a cemetery in old-town Barrington. He thought there were some interesting associates in that occasionally mowed corner. I am going to visit that site this summer and see if there is anything left.


  5. Some of the associates on the following list that range into northern Illinois might be helpful.

  6. BONAP does show Cook County as part of the range of this plant as of 2014. I wonder why Wilhelm and Rericha disagree on whether this plant is found in Cook County.

  7. My view of plants native to oak and prairie ecosystems, which have co-evolved interactions with our flora and fauna going back to before those ecosystems were even present in our Region, whether they were there all along or may have shown up more recently some how, is that they should be welcome. The development of complex and interwoven communities is a process of species settling into their own space and set of interactions in the system, and when that happens with moderately conservative to conservative (C 3 or 4 or greater) species, it is generally a sign of underlying stability and a state recovery. Species that are less conservative, regardless of origin, generally become more prominent in systems when they are in the process of recovery in response to some screw-up on our (broad sense) part or a natural stressful event that the system is going to have to recover from.

    1. Dan, I agree that "new" conservative plants should be "welcomed." I would not be surprised if many of our "new" plants were there all along, as Dennis Nyberg suggests below, but were just not noticed because they produced only enough foliage to keep the root alive during a period of stress in which relatively aggressive species put out too much allelopathic chemical or used up too much of the site's resources (sun, water, etc.) during periods of degradation (often simply from too little fire). Other "new" species may, as you imply, be just continuing the species' march north during post-glacial and now global warming times.

  8. I am happy when a previously undetected native species is identified at a preserve I care for. I can tell you are too. Nature is dynamic and new native species appear and others become locally undetectable. I studied species lists at UIC’s prairie (a 2 ha remnant) made in 1929, 1960, 1989 and 2001. There were more prairie plant species that appeared than disappeared. As you stated there are many possible explanations. I concluded it is impossible to distinguish among them, but I favor persistence of undetected plants over the seed bank.
    Concerning Dichanthelium clandestinum, as stated in the blog Pepoon(1928) reported it from Cook Co. In S&W1994 Cook has a triangle (indicating it has been seen or reported but there is no voucher specimen). The species was C =6. W&R2017 base all records on voucher specimens so no “dot” in Cook. I have no idea why the C value was reduced to 4.
    D. latifolium is present at many Palos FPCC sites. I was very surprised when found a 10m diameter patch of D. clandestinum in Spears Woods. I consider the persistence of autochthonous species more important than the documentation of such by removing individuals from the population, so I do not collect vouchers of native species.
    Because the Somme habitat is not the “sweet spot” for this species, I would not propagate it in a garden, but I would continue scything aggressive (=tall) species and see what other things show up.

    1. Dennis, thanks for good comments. Yes, I'm not surprised Woodworth Prairie experienced new species following years of good burn management. It appears that conservative species can hold on as a hard-to-notice leaf or two for a long time and then emerge with size and flowers as the "health" or "integrity" of the community recovers. I too am dubious about most prairie species holding on very long in a "seed bank."