This report - including failures and successes - was submitted to the Cook County Forest Preserves. It is unfinished and will be updated as we analyze additional data and observations.
In some cases, mowing clearly helps ecosystems heal. We in the conservation community are only beginning to learn details. Somme stewards hope these early results may contribute to the conversations about this technique.
Our general impression is that, under some circumstances, most conservative species fail to thrive in restoration settings because "aggressive" or "malignant" big plants make so much shade that the conservatives die. Mowing may help facilitate the establishment of a conservative turf in which dense conservatives prevent aggressive species from growing mortally large and dense.
The first and main study here is only five years old. There will be more reports as many of us continue sampling and analyzing results over the years.
We use both scythes and power mowers, but the work reported below is from selective cutting with the traditional scythe - a long-handled tool used for centuries to harvest grain.
We believe we may be learning about the value of strategic scything from the data below.
Experiment 1
Thirty-four years of sampling and analysis documented continually increasing quality in Vestal Grove - a bur oak woodland under restoration. After we published a study on this work, we paused our monitoring. Those 34 years had added up to quite a while, and we decided to focus on other areas and other questions for our next little while. But one set of casual observations troubled us. In some parts of this 4-acre woodland grove, the aggressive woodland sunflower (Helianthus strumosus) seemed to be reversing the trend in some areas outside the sampled transect. This possibly-poison-producing species seemed to be killing or shading out the increasingly diverse and promising turf that had been reflected in those published statistics. Woodland sunflower was also increasing in some of the permanent sampling plots, so, although we paused the monitoring, we launched a new phase of this experiment. In the past, we had kept any specialized treatments away from the initially-random transect plots from which we collected our statistics.
For a next experiment, we decided to try scything aggressive native species in half the transect plots - and seeding all plots with our standard seed mixes for all plots. (This transect included areas appropriate to many different seed mixes, but the data given here covers only the "mesic woodland" plots.)
Despite those 34 years of gradual improvement, after just three years of scything, there appears to be a significant jump in quality of the scythed plots - even though the main species scythed, woodland sunflower (Helianthus strumosus), was more conservative than the plot averages. We also scythed tall goldenrod (Solidago altissima) and briars (Rubus sp. - mostly flagelaris).
FQI refers to floristic quality:
Why such a big jump after 34 years of mostly gradual change? The difference seems stark.
But the graphs below tell a more complicated story. While they show increasing quality for the scythed plots, they also suggest that the two sets of plots ("chosen at random") were not equivalent. We had imagined that we had selected sets of plots that would be comparable, but ever since 2013 these two sets of plots (when subsequently looked at separately) seem to have been going in different directions. The plots we had chosen not to scythe had ceased increasing in Mean FQI per plot in 2011 and appear to possibly have begun to decrease in Mean cover-weighed FQI. (For cover-weighted FQI, a species with leaves covering half the plot gets more weight than a species covering 10% of the plot.) Future sampling will determine whether these plots continue to decrease in quality.
Why was that? Apparently in our published data, the larger increases in some plots were obscuring the smaller decreases in others while we looked only at the aggregate statistics. Additional sampling in future years should clarify.
To see more deeply into what's going on, in the graphs below species are divided into four groups, each represented by a different color. Orange represents the "weediest" species: think dandelion and ragweed. Red represents "somewhat weedy" native species: think black-eyed Susan and common blue violet. Blue represents high-quality species that can survive some disruption: for example wild bergamot and shooting star. Purple represents the species that are generally found only in high-quality ecosystems: for example: rue anemone or the prairie white-fringed orchid.
The numbers of conservative species in the transect (blue and purple lines) has continued to rise overall.
The graphs of changes of total cover (how much of the plot is covered by the leaves of the various species) show the species of least conservation concern to have diminished to near zero. The species that react most strongly to change in the last two samples are the high conservatives (which fell sharply) and the slightly conservative (red) and mid-conservative (blue) species, which rose slightly.
The decline in the most conservative (purple) species began before the scything of some plots and continued through the post-scything example. Perhaps it's just slow to rebound? We'll watch that group with intense interest in the future. A slightly different take is shown below: proportion of cover rather than total cover.
What's going on is complicated beyond human understanding - or ChatGPT understanding for that matter. But a look at how these four groups have done helps us think and plan.
The robustness of this data set was reduced by 1) the brief period of time studied and 2) a failed attempt to accurately locate some of the plots. We thought we probably knew where they were, but in the end we scythed only 5 of the 8 intended sample plots. We left 9 plots unscythed. (Three plots that should have been scythed were only partly scythed.) That has been corrected and will be reflected in future samples.
In all our analysis since 1985 we've used the Coefficients of Conservatism from the 1994 edition of the Plants of the Chicago Region by Swink and Wilhelm.
Hypothesis and Prediction
One test of a scientific principle is whether it has the power of prediction. We predict that the blue and purple lines will continue to rise for many years, and the less conservative will continue fall, (perhaps to the proportions they showed in 2007 through 2017?). It does not surprise us that the highly conservative species began to level off or decline in 2021 and continued in 2023. That confirms our perception and judgment that woodland sunflower was stressing these plots in 2021 and that the stress of scything might contribute (temporarily?) to more decline. Or perhaps that's wrong; perhaps it just takes that much longer for the more conservative species to increase under the sunflowers, and the unscythed areas will recover. We'll report ongoing results in future years.
The second successful example is a "found experiment." We have repeatedly scythed only about 5% (2 acres out of 40) of the restored upland savanna at Somme Prairie Grove. But, to our surprise, as we were evaluating the scything in Vestal Grove while simultaneously doing our annual monitoring of the rare (and formerly Threatened) species, the savanna blazing star (Liatris scariosa), the fact occurred to one of us (Rebecca) that the areas where this plant was doing well corresponded remarkably to the scythed areas. Two small such areas had been scythed purposely to help this species for many years. Those areas are now some of the richest on the site. But in ten other, larger areas, that were scythed to test other hypotheses, we found this conservative blazing star showing up in large numbers.
Indeed, of the 668 plants of savanna blazing star found, 576 or 86% were in the scythed 5% of the area. Many of the others grew in recently restored areas, which have turned out to be poor habitats, because as dense warm-season grasses take over, these blazing stars drop out. As Tim Bell of Chicago State University found (reference?), this species cannot compete with dense warm-season grasses in areas of full sun. Their natural habitat seems to be in the dappled light of savannas and open woodlands. Time will tell whether they will be able to find sustainable niches in such areas, or other areas, at this site. But scything clearly helps them for now.
Other Successes and Failures
We collected no data on these because it seemed not worth it. We are principally land stewards, and we have to prioritize how much time to devote to taking data. Often the results seem obvious without data. For those, we rely on observation and judgment.
Three more Successful Experiments
1. Perhaps our first use of the scythe (in the 1980s) was to combat white sweet clover (Melilotus alba) in prairie/open savanna. Covering many acres densely, there was too much for our team to pull. We scythed it below the lowest live leaf (which kills it) and before seeds were mature. It's now gone completely from those areas. We see it only in areas where brush has recently been cut, with dormant seeds in the seed bank.
2. The open savanna areas of Somme Prairie Grove have long suffered from inappropriate trees planted there decades ago. Planted species included pine, black locust, honey locust, silver poplar, birch and quaking aspen. The aspen for years grew back repeatedly and darkened large areas, despite a variety of treatments. In the end what worked was a frequently repeated variety of simultaneous treatments. We used herbicide (cut and paint and "basal bark") each fall with as much herbicide as allowed, but the resprouts seemed not to diminish. But then we started preventing root enrichment during the growing season by scything. The scythe in this case was handy because of its long reach, allowing us to treat the area with much less trampling of the quality vegetation that we hoped in time would exclude the aspen. It still appears from time to time and needs "touch-ups" but has been reduced to triviality.
3. In our savanna areas, we expect gray dogwood to be a regular part of the mix. But this shrub seems destructive in prairie restoration areas. We now treat it with the same combo approach described for aspen, above. Dogwood persists in these areas, but at apparently trivial levels.
Four Failed Experiments
1. We have sometimes scythed tall goldenrod (Solidago altissima) for a year or two in prairie or open savanna - then waited to watch results. The impacts were temporary.
2. In one area where one of our footpaths passed through a stand of big bluestem about twenty feet in diameter. We decided to broadcast a rich seed mix on both sides of the path and scythe the bluestem only one side. In early years it seemed like the scythed area was doing vastly better than the unscythed. But over a longer time, diverse vegetation took over both areas, demonstrating that the scything was unnecessary (and used time that would better have been invested elsewhere). In some areas we had similar results with tall goldenrod; it faded away as more competitive quality vegetation increased.
3. In a bur oak woodland we scythed tall goldenrod for a few years on one side of the trail, seeded both sides, and watched the results. There were none on either side. In the longer run, woodland sunflower replaced the goldenrod here.
4. Shining bedstraw (Galium continuum) is a plant of quality oak woodlands for which we never find substantial seed. So when we found a patch of this plant (about 20' in diameter) growing under dense woodland sunflower, we scythed half, left the other half unscythed, and broadcast a quality seed mix on both. After two years, there's no sign of the seed mix producing new species, and the scythed half of the bedstraw looks stressed by too much light. We can imagine that this experiment could turn out to be successful in time, but for now it looks like a failure.
As a reminder, our hypothesis is that a high quality and largely-self-sustainable oak woodland can be restored to a badly degraded area. (Most surviving oak woodlands in the tallgrass region are badly degraded. None are very high quality.) Our principal experiment to test this hypothesis is to burn at least every second year, control aggressive species, and seed a full range of woodland herbs, including the conservatives.
Acknowledgements
Scything, seeding, and monitoring for Experiment 1 by E. Kojima, C. Economou, and S. Packard with data anlysis by Karen Glennemeier.
Most work on Experiment 2 in recent years by Rebeccah Hartz.
This version of this Report prepared by: C. Economou, E. Kojima, M. Dart, S. Packard, and R. Hartz. October 1, 2025.
Scything has a decided advantage over weed whipping in the situation where the offending cut weeds need to be removed from a site. Scythed weeds lay down in a uniform direction (this makes gathering easy) whereas a weed whip scatters the plants every which way. If seeds (or flowers) are present, then scything (compared with weed whipping) is less likely to knock them off of the plants and reinforce a seed bank. The undeveloped seeds of some species may continue to mature after the plants have been cut. This necessitates their removal, again to prevent reinforcing a seed bank.
ReplyDeleteIn addition to the Liatris, another species that likes mowed vegetation is Polygala senega. It has spread from my garden to a steep west facing slope of my neighbor’s lawn. My neighbor’s lawn gets mowed, but they have not fertilized it or done any herbicide applications, other than spot spraying dandelions, in years. Senecio pauperculus also has spread from my gardens to my neighbor’s lawn. Echinacea pallida has spread from a garden into my lawn. It mostly grows right along an edge where it does not get mowed. I avoid hitting it with the string trimmer, which is probably why this coneflower has establishedso well along a low wall.
ReplyDeleteKirk, interesting comments, although your approach seems different from ours. We rarely clean up the cut vegetation. We just let it dry out where it is and ultimately burn. We don't worry about seeds, because we mow earlier in the year - before seeds form. The plants that we mostly mow are species that spread mostly by roots. We mow early in the year to prevent them from fortifying the roots as they photosynthesize. If we get a chance, we mow them again after they re-sprout. The goal is to weaken them enough that the more conservative and diverse vegetation will have the strength to outcompete them ... as they do in high-quality areas generally. Tall goldenrod doesn't have a chance against a high-quality, diverse turf.
ReplyDeleteSweet clover is another matter. At Somme it's mostly gone. But when there were great waves of it, if we couldn't get it all mowed before seed set, we'd haul it off.