Wet-Mesic Prairie: increasingly Doomed? or time for a Rebirth?

By Stephen Packard, Christos Economou, and Eriko Kojima

Wet-mesic prairie may have been one of Illinois’ commonest ecosystems. But high-quality remnants, now even rarer than for mesic prairie, seem close to gone. 

 

We’ve often wondered, are wetter prairies inherently less diverse, as some have claimed? It’s certainly a possibility. The Somme Team for decades has tried to visit and learn from all black-soil prairie types: wet, wet-mesic, mesic, dry mesic, and dry. But the high-quality prairies we found all seemed to be mesic or drier. Most of the wetter grassland areas we look at seem to be dominated by a small handful of clonal species. On the other hand, we do sometimes find small wetter spots in mesic prairies with diversity that rivals mesic prairie. (See Endnote 1.)

 

All natural areas are subject to degradation. But wet-mesic prairies face special, subtly invisible destructive forces. The bulldozer and plow are quick and dramatic. But in time the wetter prairies are destroyed also by the drainage ditch, the dam, sedimentation, and the "boom and bust" hydrology that comes from paving the watershed. When we recently asked a respected ecologist about the highest-quality wet-mesic sites in Wisconsin, he gave a site name and a glowing report but seemed to be speaking in the subjunctive. When we asked how it was doing now, his face darkened. He said it had been badly degraded by flooding.

 

On our home turf, the Somme Team in recent years has been looking a bit harder at some wet-mesic prairie areas that have been long “under restoration” by us. But really, we had more or less abandoned them except for burning as a part of the whole, though often they were too wet and the fires largely skipped them. In any case, early on, the mesic areas had motivated us to focus on them as they recovered and improved so much faster ... and then the mesic savannas captured our attention.  

But we've been increasingly troubled by the plight of our wetter areas. They had fewer species and less diversity. Did the dense “thuggish” species merely indicate poor ecological health, or were they hindering recovery? 

The dense shrubs and aggressive species could well be temporary, as in early stages of the restoration of degraded mesic prairies – eventually replaced by a diversity of rarer species of high conservation concern. Interested younger leaders helped our team to decide that our orphan wetter prairie patches deserved better help. So we got started.

Planting plugs of high-quality wetland species: how successful a solution might that be?
Christos (right) has advocated for more of it at Somme.
We think; we hypothesize; we test; and we revise approaches.

We considered changes in seed mixes. We started burning more often. We put more effort into controlling shrubs and “thugs”, monitoring results, and studying for clues.

 

We also wondered if there might be key missing elements of wetland diversity that might help recovery. We pored over species and associates lists, hoping for insights. The list below, from Wilhelm & Rericha (W&R) consists of twenty-three “characteristic species of wet to wet-mesic prairies” on “fine-textured soils” (as distinguished from lists of sand or gravel prairie species). 

The "C" column gives coefficients of conservatism. The "W" column gives wetness coefficients which range from -5 to +5. The lower the number, the wetter the habitat. 

Characteristic Species of Wet and Wet-mesic Black Soil Prairies of the Chicago Region

                

Scientific Name	C	W	Common Name
Asclepias incarnata	3	-2	swamp milkweed
Asclepias sullivantii	8	0	prairie milkweed
Calamagrostis canadensis	6	-2	blue joint grass
Carex buxbaumii	10	-2	dark-scaled sedge
Carex stricta	5	-2	common tussock sedge
Carex tetanica	7	-1	common stiff sedge
Eleocharis elliptica	10	-2	golden-seeded spikerush
Helenium autumnale	5	-1	sneezeweed
Helianthus grosseserratus	4	0	sawtooth sunflower
Hierochloe hirta	10	-2	sweet grass
Lilium michiganense	8	-1	Michigan lily
Lythrum alatum	7	-2	winged loosestrife
Oligoneuron riddellii	8	-2	Riddell’s goldenrod
Onoclea sensibilis	5	-2	sensitive fern
Phlox glaberrima var. interior	9	-2	marsh phlox
Platanthera leucophaea	10	-1	eastern prairie fringed orchid
Pycnanthemum virginianum	5	-1	common mountain mint
Silphium terebinthinaceum	5	0	prairie dock
Sorghastrum nutans	5	1	Indian grass
Spartina pectinata	4	-1	prairie cordgrass
Thelypteris palustris	7	-2	marsh shield fern
Veronicastrum virginicum	8	0	Culvers root
Zizia aurea	5	0	golden alexanders

 

Brief species lists had earlier been published by the Illinois Natural Areas Inventory (INAI). They treated the two wetter prairie types separately: 

 

Wet-mesic Prairie

Dominant plants:  Andropogon gerardi, Calamagrostis canadensis, Panicum virgatum, Sorghastrum nutans, Spartina pectinata.

Characteristic plants:  Lysimachia quadriflora, Oenothera pilosella, Phlox glaberrima, Senecio paupercaulus, Veronicastrum virginicum, Zizia aurea. 

 

Wet Prairie

Dominant plants:  Calamagrostis canadensis, Carex spp., Spartina pectinata.

Characteristic plants:  Cacalia tuberosa, Eupatorium perfoliatum, Iris virginica var. shrevei, Lythrum alatum, Sium suave. 

 

Two of the INAI's “dominant” wet-mesic species and three of the “characteristic” wet species don’t appear on the longer "characteristic" W&R list. All these lists are incomplete.

 

For Wisconsin, John Curtis lists 62 wet-mesic prairie species. Most of the Wisconsin prairies are in southern Wisconsin - closer to northeastern Illinois than are the central and southern Illinois prairies - so the Curtis list may be as useful for our Somme work as the Illinois statewide lists. 

 

Curtis found big bluestem to be a major component of wet-mesic prairie (in 40% of his quadrats). Other species that were frequent in his quadrat sampling, and that we had tended to think of as more mesic species, include little bluestem (29%), sky-blue aster (43%), bastard toadflax (30%), downy phlox (22%), and prairie dock (31%). Early on we had not put these species in our wet-mesic prairie restoration seed mixes. 

 

Why are we so interested in these lists and coefficients? They’re tools that helps us think: about goals, work priorities, monitoring, and evaluation. We want our ecosystem restoration efforts to be informed by as many facts and as much expertise as we can find. 

 

For restoration, over the decades, we’ve sought out and harvested seeds of as much of the full roster of mesic prairie, savanna, and woodland plants as we could find. Restoring high quality is not an initiative that plays out fast, but we seem to be on the road toward high-quality restoration of these mesic areas. 

 

We just haven’t given that level of attention to the wet-mesic. Perhaps now it’s time?

 

Two case studies are worth consideration. In both cases our failures are instructive.

 

Case study 1. The Pothole Peninsula

 

This area of about one-quarter acre has received special attention because for a time it harbored the world’s densest concentration of prairie white-fringed orchids (Platanthera leucophaea). It is bordered on three sides by a one-acre, u-shaped ephemeral pond and on the fourth side by prairie-like very open savanna. Its hydrology had long ago been disrupted by both a road that substantially blocks its original drainage and a small ditch that somewhat increases it. 

In the pond we successfully controlled the near monoculture of cat-tails. But disappointingly, so far as diversity is concerned, large parts of the pond are now near monocultures of iris, bluejoint grass, or bur-reed. The slightly visible open water areas (above) are where iris was recently set back by scything.

This pond had been heavily dominated by cat-tails with smaller amounts of purple loosestrife and reed canary grass. It was originally noted for two rare species – American slough grass (Beckmannia syzigachne) and Wolf’s spike rush (Eleocharis wolfii). Most seeded species "did not take." Tom Vanderpoel recommended planting some of the difficult-to-establish but most important species by plug instead of seed. That work has recently begun. 

The drier but still wet-mesic peninsula seemed for a while to respond well to our stewardship. When we began, it had a few species that suggested some surviving quality including sweet grass, smooth phlox, yellow star grass, and dark-scaled sedge. But most of the vegetation of the wet-mesic middle of the “peninsula” consisted of alien species that reflected decades of grazing. 

 

We broadcast seed of many missing species and cut brush and burned as often as we could. The area developed large populations of white-fringed orchids, small sundrops, and eared false foxglove. Because the orchid was a federal endangered species, we were nervous about the possibility that a radically changed "restored" species composition could drive out the orchid. This was probably a mistake, but it was our cautious thought. A better approach probably would have been to seed aggressively with conservative and fuel species so as to restore a sustainable, diverse turf. 

 

As it turned out, the burning reduced many alien and weedy species. Then aggressive natives including sawtooth sunflower and sneezeweed became so dense as to crowd out quality species from most of the area. When we controlled the new “thugs” – creeping thistle began to thrive, and today the area seems to hover between recovery and chaos. We focus elsewhere for a few years; the thugs come massively back;  we lop and scythe again. This area, unlike most of the site, is not improving in quality and sustainability. We believe it needs seed of missing species, especially grasses and other fuel species, and we have to try harder to get it burned regularly.  

With insufficient fire, the wet-mesic peninsula has decreased in quality. Recurring large patches of brush and aggressive forbs ("wildflowers") have shaded out its former old-field/remnant complexity. 

 

Case study 2. Northwest Prairie 

Original, remnant, degraded wet and wet-mesic prairie cover about two acres of northwestern Somme Prairie Grove (and were originally part of what is now Somme Prairie, on the other side of the railroad tracks). The original water flow from these two acres into the North Branch of the Chicago River was blocked by the railroad embankment and increased by ditching along (and a culvert under) the tracks. 

 

The remnant vegetation of these two acres when we started as stewards included all but three of the thirty-two characteristic or dominant wetter prairie species listed by W&R and INAI, but with the conservatives mostly in small numbers, mixed with aliens and brush. 

Compared to the preserve’s other grasslands, it’s been neglected. Though we’ve cut out most of the invading trees, large areas today are badly shaded by shrubs, river grape, sandbar willow, and aggressive forbs.

Most of Northwest Prairie looked like this, until recently - heavily shaded by native aggressive forbs and shrubs.

 

The biggest disappointment here had been the persistent poor quality of even the better areas. If high-quality vegetation had increased in some of these areas, we’d probably have been motivated to work more here.  

 

We probably made a mistake by withholding seed of major fuel species including big bluestem and Indian grass. Our working hypothesis in the early days was that these aggressive tall grasses were semi-thugs and that the smaller conservatives would restore best without them … and then the tall grasses would increase fast enough without help. That approach seemed to work well in mesic areas.

 

But Northwest Prairie rarely burned well, and lack of sufficient fuel was a likely part of the reason. In time we focused on insufficient burning as a likely major problem; in recent years we’ve added this area to those that are “burned annually” if possible, giving more chance that these wetter areas will actually burn on the day chosen. 

We’ve also increased our small brush control, begun scything herbaceous thugs in some areas, and increased seeding with a mix that does not omit the fuel species.

With increased burning and shrub control in recent years, original conservatives like prairie loosestrife (yellow), Culver's root (white), and smooth phlox (pink) increasingly thrive.

 

After decades of heavy brush and "thugs" just two years of better management in some areas has revealed resurgent quality. But, though lessened, the dominant vegetation remains thugs and brush.

Ox-eye daisy and black-eyed Susan add color to this railroad-side wet-mesic prairie. But large numbers of these "weedy" species show us areas most needing seed of quality conservatives.  

Ecologists who visit Somme Prairie Grove often express admiration for the restoration progress of some of our mesic and dry-mesic areas. They express no such enthusiasm for our wetter ones. With these new approaches and renewed determination to work harder, we're cautiously optimistic. We’ll report on how it goes after a few more years of effort, trial, and study.  

 

 

 Endnotes

Endnote 1. How rich were wet-mesic prairies? And what difference does it make?

Biodiversity conservation focuses on ecosystem types more than species, for a good reason. Although as shorthand we typically define ecosystem types by their plants, those plants are more important as indicators than for themselves. Plant species survive in interdependent networks of fungi, pollinators, herbivores, predators, both symbiotic and pathological bacteria, and countless more - literally countless - as science does not (yet?) have the ability to count them. Large parts of the smaller biota of ecosystems are poorly understood, unstudied, not even named. So we save them in named ecosystems.

Some of the species and relationships of wet-mesic prairies are absent or genetically different in mesic prairies and entirely distinct from those in dry prairies. Many such species survive only in high-quality remnants. If all our conservation is done in mesic and drier prairies, we lose much. A prejudice about wetter prairies being less diverse may be ill-founded.   

The INAI reported: "Wet-mesic prairie is much more diverse than wet prairie and nearly as diverse as mesic prairie."

 

As Prairie Botanist Dan Carter put it in comments on a draft of this post:  "Good wet-mesic prairie has the low stature typical of high-quality mesic prairie except for the flowering stalks of prairie dock and scattered stems (not dense stands) of sawtooth sunflower, sometimes some sparse cordgrass. Comandra abounds, sometimes wood betony (vs. marsh betony in wet prairie)." 

Dan further pointed out that, for remnant restoration, our challenge is to coax these systems away from degraded states where nutrient availability results in structure and composition derived excessively from light competition, where tall, rank species win. 

In contrast, sustainable, intact old-growth sods are structured by 1) competition for nutrients, largely tied up regardless of their amounts and 2) symbiosis, mutualism, parasitism, fungal and animal consumers and predators, etc. A healthy conservative sod depends on synergies among all the diverse biota that make it up. Once degraded, to restore that interdependent balance is especially difficult on finer-textured soils where the advantages of aggressive species are less limited by seasonal drought as they are in drier prairie types.

 

Could we say the same about the original diversity of Wet Prairie and Sedge Meadow? The INAI reports: "Wet Prairie: Plant species diversity is lower than in other prairie communities," and "The sedge meadow is remarkably homogeneous in composition and structure," which seems to be a polite way of saying "species poor." Was that always true? Or have these wetter systems just been more quickly and thoroughly degraded by disruption of their hydrologies? 

Curtis and the INAI represented great steps forward for conservation, but there is now something of a consensus that they underestimated the value and uniqueness of savanna and oak woodland - in part because they had degraded faster than other community types. Might the same be true for wetter prairies? 

References

Conservation Research Institute. Floristic Quality Assessment. A wide variety of studies available for download. 

Curtis, John. The Vegetation of Wisconsin. 1959.

Taft, John and Gerould Wilhelm, Douglas Ladd, and Linda Masters. Floristic Quality Assessment for Vegetation in Illinois. Illinois Natural History Survey.  

White, John. Illinois Natural Areas Inventory – Technical Report. Ill. Dept. of Conservation. 1978.         

Wilhelm, Gerould and Laura Rericha. Flora of the Chicago Region. 2017.

Acknowledgements

This post benefitted from editing and comments by Dan Carter of The Prairie Enthusiasts. 

Cook County Forest Preserves ecologist Anna Braum deserves credit for improved planning and coordination as does fire boss Steve Ochab for increased and improved burning. 

Thanks to Illinois DNR's Melissa Grycan for additional information about high-quality wet-mesic prairies.

Grants from the Scholl Family Foundation and the Illinois Clean Energy Foundation have helped Forest Preserve volunteers and staff make progress in these areas.