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? 

Endnotes

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.  

Acknowledgements

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