Native Thistles: Pillars of the (Natural) Community

A great spangled(?) fritillary butterfly enjoying some nectar from a native pasture thistle.

Yesterday I took the crew out for a field day to some great natural areas so they could learn some plants and see what real, healthy, managed prairies and savannas look like. Along the way we were fortunate enough to see a lot of native thistles in bloom. We saw many butterflies and bees feeding on these thistles, and I explained to them that, in addition to being excellent pollinator plants, the seeds were valuable food sources for small birds (goldfinches love thistles) and that the fluff from thistle seeds is used by hummingbirds and other small birds for nesting materials. Later, researching online I found that goldfinches are so enamored with thistles that seeing them actually has an effect on their hormone levels.

Then last night I read this article about the reintroduction of the rare swamp metalmark butterfly into a restored wetland in the Chicago area. It turns out the swamp metal mark caterpillars can only eat our native swamp thistle and pasture thistle. These valuable members of our local natural community have a lot to offer, but unfortunately they have suffered not only from habitat loss that effects all of our native species, but also from persecution due to their similarity to the weedy exotic thistles.

Exotic Thistles: America's Least Wanted

Most people think of thistles only as weeds. And it's true that some of most common, troublesome and difficult to eradicate weeds include Canada thistle, plumeless thistle, bull thistle, and musk thistle. These are all exotic species, introduced accidentally as agricultural weeds which are now problems in cultivated and natural areas alike. There are a few more exotic, weedy thistles too, such as European marsh thistle, but they are less common in this part of the state. In any event, these weedy thistles have long been recognized as pests and are on top of many noxious weed lists. There are only 3 plant species listed under Wisconsin's noxious weed law and one of them is Canada thistle.

In Illinois, both Canada thistle and musk thistle are listed as noxious weeds (not sure why they skipped the more common bull thistle), and they only bothered to put 7 other plant species on this list. Canada thistle is in fact listed as a noxious weed in 43 states!

When we at Good Oak are managing natural areas we always make controlling thistles a priority. Every farmer has a deep seated hatred of thistles, and we don't want people thinking our prairies are just 'weed patches'. Because of this common disdain for thistles, and some local weed laws (more on this later) native thistles are rarely included in commercial prairie seed mixes, despite the many benefits they can offer to wildlife.

Native Thistles: Rare Natural Gems

Wisconsin has five native thistles. Let me introduce you to them:

Pasture thistle (Cirsium discolor) is found in mesic prairie remnants, and sometimes more disturbed sites like woodland edges and yes, even pastures. You will occasionally find it in some better quality restored prairies.

Pasture thistle flower.

Pasture thistle.

The pale underside of the leaf on pasture thistle.

It looks a little like bull thistle at first glance, but the underside of the leaf is distinctively white, which is where this species gets its scientific name. A lot of overlapping silvery hairs create this bright white appearance. Bull thistle can be pale on the underside, but if you're looking at pasture thistle you will definitely think "whoa, that's white!"


Tall thistle (Cirsium altissimum) is a plant of open woodland and savannas. Note that the leaves aren't very thistle like with only small thorns. In fact, without the flowers you might not think it was a thistle at all. They have more surface area to gather more light in these semi-shade environments. The stems are covered in fine hairs, and tall thistle shares the white leaf undersides with its cousin pasture thistle.

Tall thistle.

Pasture thistle and tall thistle are the only two species that you have any chance of finding outside of a high-quality natural area. If you simply remember to look for the white underside to the leaves, you can always differentiate these two native thistles from the various weedy exotic species. These two species also bloom later than the exotic thistles. Bull thistle and Canada thistle for example, bloom from late-June through July, whereas tall and pasture thistle bloom from late July through August.


Swamp thistle (Cirsium muticum) grows only in good quality wetlands. The flowers are a darker, more vivid magenta color compared to most other thistles.

Swamp thistle.

Swamp thistle flower.

Hill's thistle (Cirsium hillii) is a state threatened species which you which you will only find in dry sandy prairies in the upper midwest. It's our shortest native thistle, typically around 18". It's also densely hairy to help it retain moisture in its dry sand-prairie habitat. The flower color is more of a true pink rather than magenta, even reddish.... unfortunately my poor-quality cell-phone photo below is not color accurate.

Hill's thistle.

Dune thistle (Cirsium pitcheri) is our rarest thistle, so rare in fact that it is Federally Threatened. It only grows on a handful of sites in Wisconsin, on stabilized sand dunes on the Lake Michigan shoreline. Its range is limited to the Great Lake shorelines of Wisconsin, Illinois, Indiana and Michigan, within a few-hundred feet from the shore. Its flowers are a pale pink, and its foliage looks nothing like other thistles with hardly a thorn to be seen. In fact the frosted-grey looking leaves look more like sage than any thistle.

Dune thistle flower.

Dune thistle's basal rossette (foliage).

Thistles: Nature's Grocery Store

As it turns out, thistles are extremely valuable plants to wildlife. Most of us think of flowers and we think of pollinators, and thistles are extremely attractive flowers to many kinds of bees, butterflies, hummingbirds, hawk moths, and many, many other small creatures. Spiders, assassin bugs and other predators set up shop on thistle flowers; pollinators can't resist the flowers so they are great spots to ambush prey.

Two species of bumble bee and dozens of small green beetles collect nectar and pollen from a pasture thistle.

As much as it pains me to admit it, this Delaware skipper is enjoying a nectar drink from a Canada thistle. Even the exotic invasive thistles can provide some value for wildlife.

Butterflies love thistles. Fritillary butterflies like this one seem to be particularly enamored by flowers in this genus.

In addition to pollinators and the predators who love them, many insects feed on the foliage of thistles, such as the above mentioned swamp metal mark butterfly. Some of these insects are specialists that can only feed on thistles and no other food source. Others are more generalist and can feed on other, similar plants. John Hilty from Illinois Wildflower has put together this list of insects that feed on thistles on his amazing website.

With at least 23 species of insects that feed on the foliage and (I don't think I'm going out on a limb here to say) hundreds of insects (and one bird) that feed on the nectar and pollen, you can see they play an important role in our ecosystem. Even more so if you consider all the insects, spiders, amphibians, reptiles, mammals and especially birds that in turn feed on the insects that feed on the thistles. Thistles aren't only a pillar of the natural community, they are a big part of the foundation of the natural food pyramid.

Separating Good from Bad: 

Our noxious weeds laws are put in place for a reason. These weeds cause economic and ecological damage. Canada thistle in particular is extremely difficult to eliminate requiring an expert, targeted approach for success. But to be absolutely clear, none of our native thistles are aggressive, weedy species. They will not spread rapidly like Canada thistle or infest over-grazed pastures like bull thistle or plumeless thistle. They really can't tolerate the heavy disturbance associated with modern agriculture and dairy production and pose no threat of economic loss to farmers. Unfortunately, many weed laws treat all thistles the same, outlawing the exotic weeds and the already imperiled native thistles alike.

For example, the City of Madison's weed ordinances which can be found in Chapter 23, section 29, paragraph 2 states that “The term 'noxious weeds' as used in this section includes the following: Canada or other thistles...” while leaving out many more harmful weeds such as, oh, I don't know, just about everything listed on the state of Wisconsin's invasive species rule NR-40.

The state of Iowa lists any and all all plants in the Cirsium and Carduus genera (what we might call all of the true thistles) as noxious weeds, regardless of origin. At least Iowa is thorough in its noxious weed list to include harmful invasive plants like purple loosestrife, common buckthorn and poison hemlock among others. By comparison Madison's weed ordinance seems somewhat haphazard.

I don't have much say in Iowa or in other municipalities around the midwest that throw a blanket ban on any thistle of any kind, but I would like to help make an effort to improve Madison's noxious weed law. If we can be clear about what plants are an economic, ecological and/or health threat to our citizens then we come up with a sound list of plants that should be banned in our community. The state's NR-40 list is a good place to start. Throw in a few hazardous plants that are already on the list such as poison ivy and the ragweeds, throw in a special request for reed canary grass which has some economic value, but is an ecological horror show, and I think we would have a good law. Then if only we could get the city to enforce it...

Critical review of management of natural right-of-ways in Madison

Last week a small urban prairie that had been painstakingly maintained by dedicated for over 15 years was mowed down by City of Madison staff, for no apparent reason at all. The prairie will recover, next year, but this year we have lost habitat for pollinator (with honey bees, native bees and monarch butterflies all seeing dramatic population crashes in recent years), winter cover and resources for birds (songbird populations have dropped by 50% in the past 50 years in the US), we lost the prairie in peak bloom(!) and we'll never get to see what this unique growing season had in store for us for fall display of asters and goldenrods. Furthermore mowing down the native perennials may leave growing space for a variety of weeds and invasive plants... I'm most concerned about the exotic cool-season grasses that we've been struggling to control in the prairie.

Below is a letter that I wrote and sent as an email attachment to my alderperson, the alderperson who's district contains the Atwood Community Prairie, city engineering staff, the Atwood prairie volunteers and members of Madison's Wild Ones chapter. Mayor Soglin will be getting a hand-delivered letter this afternoon. I thought I would share it here on my blog for all to see.

I have been angry about this subject for a while, which I am sure is evident in the text of the letter. But in retrospect, I really want to add that I really appreciate that the City of Madison is trying to add native plants to our urban landscape. "Green" efforts like these are truthfully going to be critical for the survival of our local flora and micro-fauna in the long term, and they also create an opportunity for people to come in contact with beautiful native wildflowers in their everyday life. Not to mention the psychological boost contact with nature gives people the urban air pollution these plants can help reduce and the erosion control and water filtering work they can do if property employed. Unfortunately, they're doing an extremely poor job implementing these projects, and in most cases, failing completely. So here is what I had to say.


Frank Hassler
President/Chief Ecologist
Good Oak Ecological Services
205 Walter St.
Madison, WI 53714
(608) 209-0607

August 21st, 2013

To: Mayor Paul Soglin
Alder David Ahrens
Alder Marsha A. Rummel
City of Madison Engineering Staff

Cc: Atwood Community Prairie volunteers
select members of the Madison Chapter of Wild-Ones
Russ Hefty, Conservation Resources Director

I am spurred to write to you today by the misguided mowing of the Atwood Community Prairie. I want to be clear that that action is only a single incident in what I believe has been years of mismanagement of natural areas along our City of Madison bike paths and stream corridors. You can consider this letter to be an angry letter from a citizen or a free, independent consultation. As I will explain in this letter, with the neglect of these natural areas the city violates both state law and City ordinances, and wastes a significant amount of taxpayer money on projects that are regularly failures. Some of these projects further promote the spread of invasive plants and noxious weeds in our community. Because I live on the east side of the city I will focus on sites near my home which will provide more than enough examples of the issues about which I am concerned.

The way these areas are (mis)managed causes significant ecological harm, but with changes to management strategies I believe theses areas can provide significant benefits to our ‘endangered’ local wildlife and plants, provide educational and recreational opportunities to city residents and naturally beautify our city. Madison can be a model for how other communities in our region should manage their right-of-ways.

Volunteers arrived at the prairie on Tuesday, August 13th for a workday and late-season social gathering only to find this.

The Mowing of Atwood Prairie

The Atwood Community Prairie was established in the mid-90’s with seed mix provided by the city, and has been dutifully managed by volunteers ever since. From what I can tell, the original seed mix was cheap and of low quality. However, the volunteers worked hard over the years weeding and spending their own money on plants and seeds to enhance the prairie.

Even in the past 6 years that I have lived in Madison I have noticed great improvement in the prairie. As of early last week, it was at peak bloom and absolutely full of native flowers. Then it was mowed.

So far communications between the prairie volunteers and city staff seem to indicate that it was mowed for visibility reasons. As you can see from the photos above, with sidewalks and several feet of mowed grass on either end of the prairie (up to 10’ total), there is no reason to think that there is a safety hazard associated with the prairie vegetation at this site.

Another reason given for the mowing was to control the growth of woody plants and to facilitate snow removal along the bike path. However, prescribed burning and regular maintenance by volunteers prevents tree saplings from getting established. The herbaceous vegetation here easily collapses under the weight of snow that has fallen or been plowed onto it, making mowing unnecessary for these reasons.

According to the DNR, Wisconsin has lost 99% of its original prairie habitat and 99.93% of its oak savanna. Small urban prairies like this one are critical habitat for pollinators, winter habitat for songbirds and other wildlife, and they are an overwintering site for for many beneficial insects such as solitary bees. Mowing this prairie in the middle of the peak season not only robs the public of this beautiful amenity along the bike path, it also takes critical resources away from our already imperiled local wildlife.

South and north ends of Atwood Community Prairie, respectively after mowing. Note that the vegetation at the ends of the prairie where it could plausibly cause visibility issues has been left standing.

Noxious weeds and invasive plants commonly allowed to persist and reproduce in stream and bike path right of ways, despite state laws and City ordinances demanding that they should be “destroyed”:

- All three species listed as noxious weeds by the state, Canadian thistle, hedge bindweed and leafy spurge can be commonly found flowering, reproducing and spreading along Madison bike paths and stream corridors. State law (66.0407) requires that “The person having immediate charge of any public lands shall destroy all noxious weeds on the lands.” (http://docs.legis.wi.gov/document/statutes/66.0407)

Leafy spurge is allowed to spread both by roots and by seed along the Capitol City Trail immediately south of Livingston Ave.

Canadian thistle and reed canary grass go to seed on this section of bike path between Dixon St. and Milwaukee St.

Hedge bindweed blooming along the Southwest Commuter Path immediately east of Doty St.

- Additionally, species prohibited as noxious weeds by the City of Madison’s own ordinances, including common ragweed, giant ragweed and stinging nettle are commonly found along bike paths and stream corridors. City ordinance 23.29, paragraph 2 states that “Every person shall destroy all of such noxious weeds on land which he shall own, occupy or control...” (http://library.municode.com/index.aspx?clientId=50000)

Giant Ragweed and stinging nettle are both common along the Capitol City Trail, see here together behind Olbrich Park. There are many, many more examples of these noxious weeds on trail and stream sides.

- Many plants listed as Restricted under NR-40, Wisconsin’s invasive species rule, are common along the bike paths (http://dnr.wi.gov/topic/Invasives/documents/NR40Plants.pdf). Additionally, reed canary grass, which is not yet listed on NR-40 (for economic reasons), but is arguably the most destructive invasive species in the state, is abundant, and dominates most stream corridor areas and is common along bike paths. (Examples too numerous to provide photographs of them all).

- If mowing is intended to control weeds, it should be noted that doing so this time of year has very little impact on the majority of weeds found along the bike paths, and likely increases their spread by seed, and in the cases of some of our most difficult weeds to manage like Japanese knotweed and leafy spurge, by vegetative cuttings moved around the city on mowing equipment.

- In my summation, not only is the city failing to “destroy” these noxious weeds, but in fact they have spread and increased in abundance during the past 6 years that I have lived in Madison. I believe the city is causing significant ecological harm by allowing these invasive plants to persist and spread to destroy the native plantings that the city has invested significant funds into establishing.

Recent projects to establish ‘natural’ buffer zones along shorelines have been nearly complete failures:

The shoreline restoration along Starkweather Creek from Milwaukee Street to MATC campus shows the following faults:

- less than 10% coverage by desirably native plants (that were part of the original seed mix), the entire stretch is dominated by reed canary grass and canada goldenrod.

- This is clearly the result of poor site prep and limited/poor quality maintenance that were inadequate to meet the goals of the project.

- Once established, these natural areas should stabilize and require only light regular maintenance. Unfortunately these areas are never allowed to reach this state due to a lack of proper oversight.

- In order to rectify this situation now, the area will need an intensive effort over several years to control weeds and get good quality vegetation established. This will cost many times what it would have cost if the area had been prepared, installed and maintained correctly in the first place. Good results could have been achieved with much less effort.

- Poor planning and accepting low bids for maintenance contracts from firms that were not qualified to do the work will leave the city either with this failed project or great expense being put into rectifying the situation.

Though a few native big bluestem grasses can be seen in this photo, almost every plant in this photo taken along Starkweather Creek, just north of Milwaulkee St. is either reed canary grass or Canadian goldenrod.

- Similarly, the Olbrich Park shoreline on Lake Monona has less than 10% coverage by desirable native plants. There is certainly more coverage by noxious weeds than by the plants that were seeded into the area. The reasons for the failure of this planting, and the work required to rectify the situation are similar to the above.

- Establishing prairies is indeed a challenging activity, requiring experienced land managers and an adaptive approach to managment. However, a few ‘rules’ of successful prairie establishment are that thorough site preparation to eliminate weeds before seeding is critical to success, and that careful monitoring and aggressive weed management are necessary during the first few years of establishment.

The vegetation establishment of the slope erosion control project along the bike path Starkweather Creek spur behind Olbrich Park is off to an extremely poor start, and destined to fail if action is not taken immediately:

-Though I was initially pleased to see the tangle of invasive brush removed from this area and the rampant erosion issues here addressed, it is clear that poor site preparation and a complete lack of vegetation maintenance on this slope will result in a failure to establish the native prairie plants that were seeded here, and the site will end up dominated by noxious weeds and invasive plants if corrective actions are not taken within the next few days.

- It is clear from abundant weeds including barnyard grass, foxtail grasses, velvet leaf, common ragweed, giant ragweed, and others, that the topsoil used for this project was not “clean”, but instead was dense with weed seeds.

- Since seeding has been completed here, no maintenance work has been done. Annual weeds up to 6’ fall now dominate the seeded area. Typically one would plan on doing 2-4 mowings in the first growing season of a planting like this. The shade produced by the dense annual weeds has undoubtedly killed many prairie seedlings which only grow a few inches above ground in their first growing season and require direct sunlight for growth.

- The edge of this slope along the bike path has since been mowed. However, the dead plant material is so thick it completely covers the ground, smothering all vegetation below. Also, most of these weeds have already developed seeds. Mowing at this stage does nothing to control the reproduction of these weeds, and may in fact increase the amount of viable weed seeds that reach the soil.

- At this stage the only possible course of action to prevent a complete failure of this planting would be to cut down existing vegetation, and remove it all from the site so as to limit the amount of weed seeds that are able to drop on site. I strongly urge that this work take place within the next few days.

- I strongly urge that this area be re-seeded, be covered with fresh erosion matting in spring of 2014 and that a regular maintenance regime (including regular mowing of annual and biennial weeds and spot herbicide treatment of perennial weeds) be carried out for the first several growing seasons in order to promote good establishment of native plants in this area.

This area, seeded in the spring of 2013 is completely dominated by annual weeds. The only plants that are visible in the area which were part of the intended seed mix are the annual oats (brown in color, center of photo).

Extremely poor maintenance of most rain gardens:

The City of Madison proudly touts its rain garden program, and continues to expand the number of rain gardens around the city. While this program is well intentioned, many of the rain gardens are poorly maintained, if at all. Many critics of rain gardens consider them ‘weed gardens’ and by not maintaining the rain gardens properly, especially in the first few years of growth, the city is proving these critics right. I find this particularly frustrating because I believe that the establishment of rain gardens and other methods to cut run-off into our lakes and streams is critical if we are to improve the quality of our waters. Below are a few (among many) examples of poor rain gardens that need to be rectified:

- Goodman rain garden has weedy trees (boxelder, hackberry, walnut) 4-5 years old. Meaning that the contractor hired to maintain this rain garden has failed to do an adequate job for many years in a row. Crown vetch, reed canary grass and other invasive plants have gone unmanaged at this site for 3-4 years, despite the fact that I alerted city staff to this issue about 3 years ago. Ragweed (the pollen of which causes hay-fever allergies) has been allowed to bloom every year for at least the past 5 years (these would have probably been eliminated from the site by now if they had been managed early on). Lack of care is obvious and embarrassing, especially considering the interpretive sign describing rain gardens at this site.

Above: Many weedy trees displace native perennials in the Goodman rain garden. Removing these trees should be a simple, basic part of maintaining the site, which has been neglected.

The invasive crown vetch persists in the Goodman rain garden just beyond the mower’s reach, and has spread significantly over the past several years with no effort made to control it.

- Similarly the rain gardens at the end of Ivy Street, across from Sherry Park, are in very poor condition. The rain gardens were dug too deep and with very steep sides, which would have to result in instability and erosion on the sides of the rain gardens. Even though they were only planted about 3 years ago, it appears that they have received almost no maintenance and have many more weeds in them than native plants.

Though native plants are still present in one of the Ivy St. rain gardens, noxious weeds such as Canadian thistle and stinging nettle are pushing them out, with no effort taken to control them.

Though common ironweed (purple flowers) is prominent in the other Ivy St. rain garden, the bulk of the area is covered by various weeds and not the native plants which were planted there.

- A few rain gardens in the city seem to be in fairly good shape. For example, those located in Brittingham Park are fine examples - I suspect because they were installed and managed by qualified professional ecologists during their first several years of existence. Also their larger size may promote ecological stability. I suggest examining what has gone right in some rain gardens and wrong in others to develop a plan of action going forward to maintain existing rain gardens and establish new ones.

Recommendations: 

- More careful planning, preparation and maintenance needs to be done to insure success of various “natural” plantings on shorelines and right-a-ways around the city. The city should expect to invest more up front for more thorough site preparation, better seed mixes, and more intensive maintenance for the first few years of a planting in order to see a successful planting with lower maintenance costs down the road.

- Concerted efforts must be made to eliminate noxious weeds and invasive plants on public property.

- All field staff should learn to identify noxious weeds and invasive plants and be trained in targeted control methods. They should also learn to identify native prairie plants that are commonly included in seeding mixes around the city. Being able to identify a couple dozen weeds and a couple dozen prairie plants should be a basic qualification for anyone managing vegetation for the City, even if it’s just running a riding mower.

- The City continues to hire under-qualified landscapers to conduct installation and maintenance work in these natural areas within the city. The Goodman rain garden is a prime example. The City needs to develop a process to screen for qualified contractors to bid on natural areas management activities. With well over a dozen firms (including Good Oak Ecological Services) that specialize in invasive species control and natural areas management servicing Madison, there is no lack of qualified experts in this field in our region that could do good quality work for the city.

- City engineers seem quite competent in the field of civil engineering, but vegetation management is an entirely different field of expertise. The city should consider the following options: 1) Hire a consultant to help develop the vegetation management aspects of the RFP and to monitor the site preparation and maintenance work. 2) Hire additional staff with expertise in natural areas management and weed control specifically to plan and manage these reconstructed natural areas around the city. 3) Increase the funding and man-power available to the Parks Division’s Conservation Resources Director so that qualified personnel already working for the city can take charge of managing these areas. Please note that the Conservation Resource crew currently has insufficient resources to manage the natural areas they are already tasked managing. As such, the increase in resources to this group would need to more than compensate for the increase in responsibility.

- The city should get existing rain garden and natural corridors on track before attempting to add additional management units.

Sincerely,

Frank Hassler
Concerned Citizen
Professional Ecologist