This report - including failures and successes - was submitted to the Cook County Forest Preserves. It is unfinished - in process - and will be updated as we analyze additional data and observations.
In some cases, mowing clearly helps ecosystems heal. It's a medical treatment. Like bed rest or flossing teeth or physical therapy.
We in the conservation community are only beginning to learn details of this treatment, as with so many others. We 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. In other cases, the troublesome plants are "allelopathic" - that is, they make chemicals that are poisonous to other plants. The conservative species, which are the heart of healthy, diverse ecosystems, know how to deal with such stressors under natural (high diversity) conditions. But, as with a human patient after major surgery (or the plant counterpart: after major invasives removal), an ecosystem may need temporary "intensive care" to avoid a variety of possibly chronic or fatal disorders.
Thus, 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 2011 or 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 after 2011 and appear to 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 the unsythed plots continue to decrease in quality.
We had thought that these plots had continued to gain in quality. But, 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, based on their
coefficients of conservatism (C), 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) have continued to rise overall.
The graphs of changes of total cover (how much of the plots 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 these species are just slow to rebound? We'll watch what happens to that group with interest. A slightly different take is shown below: proportion of cover rather than total cover.
What's going on may be 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 (just three years) 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 fully scythed only 5 of the 8 intended plots. We purposely left 9 plots unscythed. 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 already stressing these plots in 2021 and that the stress of scything might contribute (temporarily?) to more decline. Or perhaps that interpretation is wrong; perhaps it just takes that much longer for the more conservative species to increase under the sunflowers, and perhaps the unscythed areas will recover. We'll report ongoing results in future years.
How fast and how far can restoration go in restoring ecosystem quality? This is not a trivial question. For sustainable conservation, many “natural area” remnants seem to be too small – especially for animal species (e.g. pollinators) that may be important and may drop out, to the overall loss of ecosystem health. How much effort should go towards attempts to expand small high-quality habitats … compared to large “good quality” (grade C and low B) habitats? We need to increase capacity, but in the real world, there will always be finite amounts. Resources devoted to remnants will have to be balanced with resources devoted to recovery and expansion. Is it more important to double the Grade A acreage … or to surround it with ten or one hundred times the acreage of grade C? Or do we devote ourselves to increasing that C acreage to B? How different are these considerations for one-acre remnants … compared to initiatives like the Markham Prairies, Nachusa Grassland, and Goose Lake Prairie, where small remnants are surrounded by hundreds or thousands of acres of ongoing restoration?
The second apparently 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 - for all species. 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.
Tim Bell and
Nathan Schroeder found that this species competes poorly 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 these rare plants 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 some of 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 and open savanna. Covering many acres densely, there was too much for our team to pull. We scythed it a) below the lowest live leaf (which kills it) and b) 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, despite a variety of ongoing control attempts, for years grew back repeatedly and darkened large areas. 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 and diminishing 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. Perhaps a longer course of treatment would have worked? Or perhaps the best treatment is simply good overall management and time.
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 much 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).
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. None were perceived on either side. In the longer run, woodland sunflower replaced the goldenrod here.
4. Shining bedstraw (Galium concinnum) 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 demonstrate successes 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.
Thanks for sharing this report. I wonder if you could describe the preferred type of scythe and technique your group has settled on in a little more detail. The tools in the picture look a little different from what comes up when I search around for scythes online.
ReplyDeleteWhat kind of scythes? Good question. We use blades - but not handles - from https://scythesupply.com. The blades are made in Austria - where scythes are still used by farmers. But the long handles (technically "snaths") that are for sale don't work well for us. We buy Scythe Supply's metal attachment, but for the actual snath, we use a dowel or, increasingly a piece of buckthorn or ash that we've cut as brush.
DeleteSome of us like the grass blades. Some of us like the all-purpose blades. We don't use the brush blades, as we find that other tools work better for brush.
The scythes used by the group with which I work have lightweight, tubular-aluminum shafts (the snath) with one wooden grip for easy swinging. They have steel blades which are kept sharpened using files and sometimes with sharpening stones. Sharpening the blades before cutting reduces both the cutting effort required and the fatigue that scything induces. If and when removal of the cut material is necessary, then the process is most efficiently accomplished if one person scythes and another gathers up the cut material. Otherwise, stopping to gather material gives a scyther a bit of a rest break, but it also reduces the area that can be covered in the time that is available for the work that needs to be done.
DeleteWhen you started discussing scything aggressive species a few years ago, I decided to try cutting tall goldenrod with pruners to see the result. In a disturbed area in the corner of my yard I cut tall goldenrod off at ground level. I put flags by the cut stems. Since this was a few years ago, so I don’t remember when I cut the tall goldenrod or how many times they were cut. I do remember that many of the tall goldenrods were killed. After this post, I looked at the area and there are a few tall goldenrods present. At least one had a flag next to it and therefore probably survived being cut off at ground level.
ReplyDeleteIn garden situations, I remove tall goldenrod by the root. This is much more effective than cutting stems off at ground level. This gives the long-lived prairie plants enough time to establish, so they can hold their own when tall goldenrod reinvades. After a few years of not removing tall goldenrod, it has reinvaded and is again blooming. Oddly, in a different garden I burn annually there is no tall goldenrod. Although other weedy species like sow thistle and old field aster have become problematic.
In a restoration on overly-high-fertility organic-rich soil staff of a local nature center used a string trimmer to cut tall goldenrod. They did this for two years. The tall goldenrod returned the year after it had been cut. In this organic rich soil, the tall goldenrod was only made shorter by annual cutting.
In this same restoration, I removed tall goldenrod by the roots. I sowed seeds. After the second year, the seeds where growing. However, I stopped controlling the tall goldenrod. The seedlings had not gotten big enough to hold their own against the tall goldenrod. Tall goldenrod reinvaded and out competed all the seedlings.
The moral of the above experiences is cutting tall goldenrod may control it if the soil is poor but will not control it on overly nutrient rich soil. Also, if tall goldenrod is controlled, then control must continue for long enough that prairie species can reach a size that tall goldenrod will no longer be able to out compete them. Possibly, fire will keep tall goldenrod from reinvading. This has been the experience in my garden and Dr. Betz’s experience at Fermi Lab.