Stewardship Begins

by Carl Strang

Earlier this spring I began my work as volunteer steward of McCormick Woods, the main forest at St. James Farm Forest Preserve. The stewards provide backup and extension of the ecosystem restoration work by Forest Preserve District staff. The McCormick Woods ecosystem is the highest quality forest in the western half of DuPage County, and the District has put considerable effort into its restoration, but there still is plenty for volunteers to do. Invasive shrubs and herbaceous plants are established in significant portions of the forest, there supplanting the diverse native plant and animal community.

I have had the help of two other volunteers, Wayne and Bob, and we have made a good start. We began by focusing on garlic mustard, an invasive and allelopathic biennial, in two large areas where native plant diversity is excellent and garlic mustard is not yet well established. We took the bushels of pulled garlic mustard plants and dumped them in two locations, hoping to make progress against the forest’s biggest threat: goutweed.

Goutweed is a perennial member of the parsley family (Apiaceae, formerly Umbelliferae).

Goutweed was imported from its native Europe and commonly is planted as an ornamental ground cover. Apparently it was used in the landscape around the McCormick residence at St. James Farm. Unfortunately it spread into the adjacent forest, and significant colonies of the plant have supplanted the native forest flora in places. Repeated applications of herbicides by District staff may have slowed it down, but do not kill it. Stronger herbicides that would kill it also would threaten the trees.

I selected goutweed colonies in two locations as garlic mustard dump sites. I wanted to see if masses of pulled plants might smother the goutweed, hoping also that allelochemicals might leach out and inhibit goutweed growth. The goutweed has proven to be resilient.

Goutweed leaves pushed up through the piles of garlic mustard in the first location, which had not received an herbicide spray earlier in the spring.

The second dump was in goutweed that had been hit by herbicide. It is too soon to say whether the results are any better.

At some point I want to take measurements to see how fast the goutweed colonies are expanding, and whether these efforts slow that growth.

Now that the garlic mustard pulling is done for the year, we have shifted to another location and are cutting common buckthorn and Amur honeysuckle. That part of the forest still has a good diversity of native woodland plants hanging on beneath the invasive shrubs.

Here is part of the area we have cleared. Increased light levels should allow native plants to expand their populations.

We are creating a brush pile of the cuttings that later will be burned.

There are no goutweed patches in that part of the forest. Burning brush piles would kill the goutweed beneath them.

I was inspired to take on the stewardship job by the diversity of life in McCormick Woods. Some recent photos:

Shooting stars have popped up here and there where they were released by the removal of invasive brush.

Giant swallowtails appear occasionally at St. James Farm.

A recent addition to the preserve species list was this Zabulon skipper.

Garlic Mustard Plot Closing

by Carl Strang

As I begin the slide toward my retirement next August, I have begun to tie up some loose ends. One of these was the need to pull markers I had left at all the garlic mustard study plots I had established over the years at Mayslake Forest Preserve. That research was very satisfying, confirming experimentally that stands of garlic mustard can be removed effectively without use of chemicals or tedious hand pulling of individual plants (the results were last summarized here in 2013).

Some of those plots go back 5 years, and I was surprised at how little garlic mustard had returned to them.

Here is one of the plots. Most of the green is from things other than garlic mustard.

Here is one of the plots. Most of the green is from things other than garlic mustard.

A close-up from another plot. Only a few widely scattered first-year garlic mustard plants were present in each plot.

A close-up from another plot. Only a few widely scattered first-year garlic mustard plants were present in each plot.

These plots were shaded, which would inhibit growth, and the limited number of plants suggests that these were new infestations which had not established much of a seed bank.

 

Sound Ideas: Garlic Mustard-O

by Carl Strang

The snow is melting, and before too long the warmth of the new season will bring its gardening and restoration tasks. These include the weeding of garlic mustard.

This invasive biennial is a bane of woodland restorations.

This invasive biennial is a bane of woodland restorations.

As researchers have found (and I have illustrated through this blog), well established stands of garlic mustard can be killed by mass cutting of the tops close to the ground as they are about to flower. Hand pulling is effective, but only efficient when scattered plants have begun to appear. Hence this week’s song still has some relevance:

Garlic Mustard-O by Carl Strang copyright © 2006

Here is a spot, a nasty little spot, it’s filled with the garlic mustard-o.

My arms are torn, and I am so forlorn, for I’m pulling in the black raspberry-o.

It’s Garlic Mustard Time

by Carl Strang

We have entered the time of year when removing garlic mustard is a popular pastime of people wishing to improve woodland plant communities. Garlic mustard is an Old World import that has the unpleasant characteristic of poisoning the plants around it (including trees), and spreading to dominate the forest floor.

Garlic mustard on the verge of flowering

Garlic mustard on the verge of flowering

In early spring it’s nice and green, and has arrays of small white flowers, but it quickly goes to seed and dies, leaving the area barren except for its dead brown stalks. One of its weaknesses is that it is a biennial, which limits its rate of spread when it first invades an area. In its second, flowering year it can be uprooted and removed.

As I have outlined in this blog through descriptions of various experiments over the past several years, the plants can be clipped or pulled, depending on the point of the season. That study was inspired by a paper (Pardini, Eleanor A., Brittany J. Teller, and Tiffany M. Knight. 2008. Consequences of density dependence for management of a stage-structured invasive plant (Alliaria petiolata). Am. Midl. Nat. 160:310-322) claiming that uprooting is unnecessary, and sharing experimental results in proof.

My own research has confirmed that conclusion, though timing plays a role. As long as the second year plants are rosettes (through March into some point in April), uprooting is more effective than cutting. Once the stems elongate and begin to bloom, clipping at ground level kills the plants as effectively as uprooting them.

In last year’s final experiment I applied a grass whip to cut green fruiting plants at two heights, 10 inches or so above the ground, and below the lowest leaves (2-3 inches). Both were effective, but the lower level cutting (which was no more difficult) was extremely so, with only about 1% of the plants producing minimal abortive looking fruits.

This week I looked at those plots again. The higher cut area had a few scattered seedlings. The close cut area had practically none. In contrast, surrounding untreated areas were dense with seedlings.

The close cut area a year later. The point was not to make this place safe for creeping Charlie (most of the green in the shot) but to eliminate the garlic mustard. The method would appear to do so efficiently.

The close cut area a year later. The point was not to make this place safe for creeping Charlie (most of the green in the shot) but to eliminate the garlic mustard. The method would appear to do so efficiently.

Just outside the experimental plots, the ground is thick with garlic mustard seedlings (most of the green in this photo).

Just outside the experimental plots, the ground is thick with garlic mustard seedlings (most of the green in this photo).

I’ll close with a reference to another paper (Chapman, Julia I., Philip D. Cantino, and Brian C. McCarthy. 2012. Seed production in garlic mustard (Alliaria petiolata) prevented by some methods of manual removal. Natural Areas Journal 32: 305-315). They conducted experiments to see whether uprooted and cut garlic mustard tops can still produce viable seed. They likewise found support for killing the roots by cutting off the tops. A few produced tiny sprouts that died without reproducing. No seeds were produced by plants uprooted when flowering. Cutting off the roots did not affect seed production in the tops. Early fruiting plants produced more viable seeds after cutting than did late fruiting plants. Plants that were hung or piled produced fewer seeds than those scattered on the ground. They did not measure seed production in undisturbed plants. They mention that cutting plants close to the ground with a string-trimmer should be effective. Pulling or cutting before the plants are fruiting should require nothing more, but fruiting plants should be removed from the site. In remote places where hauling away the mass of entire cut plants is impractical, it should be enough to remove the fruiting parts and take them away for disposal.

Garlic Mustard Results

by Carl Strang

Last week I returned to the garlic mustard plots I had treated in the spring, to assess the results of my mass cutting experiment. This was the finale of a series of experiments to compare alternative manual removal methods for this invasive biennial. In one plot of approximately 10 square meters I used a grass whip to cut the plants at a height of 10-12 inches, removing the fruiting tops but leaving some foliage. I found that 58% of these plants subsequently had flowered and produced a few seeds, though there was very little reproductive output, especially compared to intact plants.

This is the typical paltry fruit production on one of the cut plants.

With only a little more effort and time, cutting the plants closer to the ground and removing practically all the leaves is feasible. In the other study plot, about the same size as the first, I had cut the plants at a height of 4-6 inches. There, only 1% of the plants produced a tiny number of seeds. The difference was stark, but I calculated the chi-squared test statistic anyway, using the taller-cut plot results (representing a practice I have seen used in restoration work) as the basis for expected values in the shorter-cut plot. The value of 390 is, of course, highly significant.

The short-cut garlic mustard plants on July 6 were almost all naked dead stems. The green leaves all belong to other plant species.

Circumstances had prevented my doing this assessment as early as I would have liked. The stems all were dead, and some had been trampled to the ground (the shorter ones more so than the taller ones), so that the total numbers of stems in the two plots were different: 472 in the higher-cut plot, 297 in the shorter-cut plot. To the eye they had been identical at treatment time. Nevertheless, I feel confident in recommending the practice of mass cutting garlic mustard plants at a height of 4-6 inches as they are completing their blooming period. The cut tops need to be hauled away, as they potentially could release some seeds as they dry. As established in the early experiments, such late cutting of the plants kills them. The common practice of uprooting garlic mustard, though effective, is less efficient. It should be reserved for situations where mass cutting would cause undesirable harm to other species (for instance, in high quality areas where the garlic mustard is just becoming established), or where the removal must be done early in the season.

Garlic Mustard Setup

by Carl Strang

One of my ongoing studies in recent years has been a pursuit of best practices for manual removal of garlic mustard, an invasive biennial that is one of the banes of terrestrial plant community restoration. Following an early study by researchers in downstate Illinois, I have confirmed that while uprooting of plants is effective, and is the most effective method early in the season, clipping the tops at ground level works equally well late in the season, and none of these practices increase garlic mustard seed bank germination as far as I can tell. (If you want to review my study to this point, go to the left frame of this blog and do a search on “garlic mustard.” You will scroll through all the posts in which the plant is mentioned. The first one in this study is dated March 20, 2009).

Individual hand-clipping of plants is inefficient, however, and so this year I wanted to test how well mass cutting of late-season garlic mustard plants replicates the earlier results. The problem that arose was my back strain, which made me leery of swinging the grass whip that was my chosen tool. The pressure was on, however, as this year’s early season had the plants developing apace, and so as they were showing their final flowers I decided to suck it in and give it a try. I wasn’t able to crouch down and mark out study plots as I have done in the past, and I wasn’t willing to do a lot of plots, so I settled for cutting and raking two adjacent areas dominated by dense garlic mustard plants. One of those areas I cut close enough to ground level to eliminate all the leaf-bearing parts of stems.

These photos are from a couple weeks after the cutting. The leaves here are those of creeping Charlie. At this point there is no recovery of garlic mustard evident.

It didn’t take a lot of effort to remove a volume of plants with this close-cut variant. In the other plot I cut the plants at around 10 inches above ground level, a height selected to match the practice I have seen used by some restoration workers.

Here you see the cut stems.

By the time I got around to taking the photos, adjacent garlic mustard plants had completed flowering and were ripening their fruits.

This gives an idea of the density of garlic mustard in the study plots prior to cutting.

I am giving the test areas several weeks to show any recovery by cut plants, and will share the results in late June.

Odd Plant Notes

by Carl Strang

Today I have a couple botanical notes to share. First is a plant I ran across at Mayslake which didn’t quite match up to any species’ description. The flower heads took it to the sow thistles, genus Sonchus, and the yellow heads were small, but the leaves were very odd.

The leaves had large triangular end lobes, with narrow fringes otherwise.

There were several individuals just like this, in the shaded south savanna. After weighing all the possibilities I eventually went with Sonchus asper, the spiny sow thistle. The basal lobes wrapping around the stem are rounded, with only their teeth making them look pointed. Though less spiny than is typical for this species, I attribute that as a response to the low light, limiting the plant’s resources for producing spines.

Nearby, I was struck by the lush growth of a ring of first year garlic mustard plants.

They formed a narrow zone around the scar where a pile of cleared brush was burned last winter.

The minerals leached out from the ash clearly are benefitting these plants. They also may be reaping a nutrient harvest from underground parts of plants killed or weakened by proximity to the fire. The garlic mustard plants themselves grew from seeds this spring, well after the fire had been doused; the seeds clearly could withstand the nearby heat, though any directly under the fire were destroyed.

Garlic Mustard Seedlings 2011

by Carl Strang

As chance would have it, there are very few patches of second-year garlic mustard plants at Mayslake Forest Preserve this year, and none that will suit the next stage in my experimental study of best methods for manual removal of these invasive European biennials. There are, however, abundant seedlings.

This is a typical scene where garlic mustard is established. Seedlings appear very early in the season.

Last week I paid a final visit to last year’s experimental plots to count seedlings. These are areas, divided into square meter units, in which I either uprooted plants, or clipped them at soil surface level, or left them alone as controls, in April. I have found that uprooting garlic mustard is effective in March or April, and clipping also is effective but surprisingly so in April (practically none survive).

In the process I am looking into the possibility that uprooting plants disturbs the soil and increases seedling germination, a possible negative side effect. Earlier I found that pulling tiny second-year plants in March does not encourage additional seedling germination. Uprooting larger second-year plants in April disturbs the soil more. I found last year that same-year seedling germination is not increased, however. Would the same be true in the following season?

The bottom line answer is, yes. The total number of seedlings in 9 square meters of controls was 6125 (range 262-1444, median 724). Clipped areas produced 5954 seedlings (range 249-1397, median 491). Uprooted squares contained 5595 seedlings (range 150-1286, median 515). Differences were not statistically significant. That puts to rest, in my mind at least, concerns about the common practice of uprooting.

So, I am done I think with hands and knees work. The next stage, which now will need to wait until next year, will be to try clipping with a cutter that allows more efficient, faster removal than one-by-one hand clipping.

Garlic Mustard Follow-up

by Carl Strang

I have a final bit of data to share for this year in my study of garlic mustard removal methods. I returned to this year’s study plots in September to see how much the seedlings had thinned out over the summer. Thinning always occurs, as various mortality factors (including competition among the seedlings themselves) take their toll. I did not expect the dramatic degree of thinning I observed, however.

The bare soil you see in this study plot corner was typical. Median counts were 0 seedlings in the square-meter plots for pulled treatments, clipped treatments and controls. Totals in the 9 square meters for each category were 17 seedlings in clipped squares, 4 in pulled squares, 5 in controls.

That compares to respective totals in May, the last time I counted seedlings, of 700, 609, and 575. I should say that this is a different result than I saw last year. Last year’s May totals were 1002, 747 and 214. Last year’s end-of-season totals were 107, 236, and 3. The two years had much different weather, so I cannot say that this difference is due to the year, to the slightly different plot locations, or to the difference in treatments (treatments applied in March 2009, April 2010). On the other hand, the controls produced similar results in the two years.

The only data I neglected to report last spring, by the way, were the over-winter survival numbers of those end-of-season first year plants. The respective totals were 97 plants in clipped treatment squares, 226 in pulled treatments, and 4 in controls (obviously I missed one the previous fall). Over-winter survival thus was good in all three cases; the main thinning occurs during that first growing season.

Garlic Mustard Study Continued (Seedlings)

by Carl Strang

In the previous post I looked at this year’s results in my study of alternative manual removal methods for garlic mustard, an invasive biennial. In summary, uprooting the plants is effective any time. Cutting them off at ground level also is effective, but more so in April than in March. Today I want to shift the focus to first year plants, or seedlings.

I have been following the development of seedlings in my study plots, in part out of general curiosity and in part to test the possibility that uprooting second-year plants stimulates additional seed germination. Last year, when I uprooted relatively small second-year plants in March, there was no increase in seedlings then or in the following year. This year I uprooted the older plants in April, when they were larger, so there was a greater possibility of impact.

Numbers of seedlings prior to treatments in study plot square meters were not different statistically, with median counts of 64 in clipped squares and 32 in uprooted squares (I did not count seedlings then in controls, as the process would have been too much of a disturbance). When I returned to assess the results at fruiting time I found median seedling counts of 65 in uprooting treatments, 67 in clipping treatments and 47 in controls, with enough overlap in ranges of counts that there were no statistically significant differences in pairwise comparisons.

Last year I found that seedlings in control squares were fewer at the end of the reproductive season, and had been suppressed in their growth. This year I found no such difference. This implies that the advantage of seedling suppression is achieved by waiting until April to remove second-year plants. Also, pulling second-year plants in April did not increase numbers of seedlings in the same year. I will need to return next spring to see if the soil disturbance has an effect the following spring.

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