Gorham Springs (aka Duck Pond Springs) on Nakoma Road: a review of “invasive species impacts”

Gorham Springs as it flows into a pond in the UW-Madison Arboretum, as it appeared in September, 2016.

Nakoma Road and  Monroe Street are two of the busiest thoroughfares in Madison.  But just a few feet away from where these two traffic arteries intersect, is one of the few remaining natural springs in the Lake Wingra Watershed.

Just below the graceful curve of Nakoma Road and beyond the old stone wall that guards the Arboretum, and at the base of Spring Trail Road, flows a scarce and valuable source of cold water for Lake Wingra–the Gorham Springs.    In a watershed where once there were over 30 springs, it is now one of only 13 that remain.

More Than Just One Spring

The Gorham Springs (also known as Duck Pond Springs) is actually a complex of 5 springlets that flow from deep underground and emerge at the base of the stone wall and into the pond in the UW-Madison Arboretum, across Nakoma Road from the old Spring Trail Tavern.  Because the single source of upwelling groundwater is divided into 5 spring channels, Gorham Springs has never had the fast-flowing appearance of some other springs in the Lake Wingra Watershed.

Watercress and forget-me-not growing in one of the vegetation-clogged spring channels of Gorham Springs (aka Duck Pond Springs) as it appeared in September, 2016.

Aquatic Weeds

What is different this summer is that the spring channels are so thoroughly clogged with forget-me-not and watercress that a visitor can’t even see the water.  Although these species have grown in the Lake Wingra Watershed for many years, and probably as long as Europeans have been in the area, the extent of their abundance this summer is alarming.

Watercress (Nasturtium officiale) and Forget-me-not (Myosotis scorpiodes) are described in “Wildflowers of Wisconsin and the Great Lakes Region” (Black & Judziewicz 2008)  as “introduced–naturalized and ecologically invasive.”   Pictured above and below, they like to grow in, or near, cold-water streams.

One of several springlets that are part of the Duck Pond Springs complex, as it looked in September, 2016.

Perhaps part of the reason the springs are clogged with aquatic weeds is that the spring does not have a powerful enough flow rate to flush them out, or to at least push them aside.   The flow rate of Gorham Springs (measured as cubic feet per second) is relatively slow compared to, say, the Council Springs at nearby Arbor Drive, or Big Spring across the lake.  Or, alternatively, the aquatic plant growth is slowing down the flow rate?  No one knows.  At least, I have not found any research on the topic.

What Problems Are Caused by Watercress and Forget-me-not?

I admit that watercress and forget-me-not are not garden beauties and seeing them clog a cold-water stream is not appealing; but, are they ecological problems or just aesthetic issues?   Because these two plants are considered invasive by the WIDNR, periodic efforts have been made to physically remove them from the Gorham Springs area.  But a manager of such a situation needs to decide if the abundance of these two plants is an aesthetic issue or can they cause real and documented ecological harm–a manager needs some proof that a control effort would be worthwhile and would be successful before deciding to invest in such an effort.

The Claims of an Ecological Threat

So, let’s see what the invasive species literature says about watercress and forget-me-not.   One claim for the invasive status of forget-me-not and watercress is found in “Invasive Species of the Upper Midwest” (Czarapata, 2005).   Czarapata lists both watercress and forget-me-not as invasive species and describes control measure but offers no documentation as the nature of their ecological threats other than that the Wisconsin DNR lists the two species as “invasive”.

Another claim comes from Black & Judziewicz (2008) in which they describe both watercress and forget-me-not as “introduced–naturalized and invasive” as “defined by the Wisconsin Department of Natural Resources and the Wisconsin Herbarium.”

The United State Agriculture Department (USDA) Natural Resources Conservation Service plant database lists forget-me-not (Myosotis scorpiodes) as invasive but this is based upon only the recommendation of the Wisconsin DNR invasive species section.

And finally, the Wisconsin Department of Natural Resources lists forget-me-not as an invasive species  and classifies it as “Restricted” under NR 40, DNR’s invasive species rule. The rule means that a person: “Cannot transport, transfer, or introduce without a permit.**Possession is allowed except for fish or crayfish. Control is encouraged but not required.”

The WIDNR cites several ecological threats posed by forget-me-not, including:
1.  “Aquatic forget-me-not can quickly crowd out native plant species and is able to form large monocultures, especially in situations where it is in or near a stream. This, in turn, affects community composition by reducing the number of native herbs.”
2.  “This species has the ability to escape water gardens and ponds and grow in undisturbed and natural environments. It can grow in wetlands, forests, bogs, swamps, marshes, lakes, streams and ponds.”
3.  “Aquatic forget-me-not is difficult to control due to its mechanisms for spreading. It is capable of abundant reproduction through spreading stolons (runners) and abundant seed production.”
4.  “Due to habitat competition, aquatic forget-me-not poses a threat to two threatened and endangered Wisconsin native plants; the threatened intermediate spike sedge (Eleolcharis intermedia) and the endangered winged monkey flower (Mimulus alatus).”

Watercress is not considered an invasive species by the Wisconsin DNR.

The Evidence

Through my investigations, here is what I have been able to find so far.  There may be other evidence out there that I am not aware of,  so if anyone if familiar with more recent literature, please let me know. I’m always eager to learn more.

The primary piece of evidence for the ecological harm caused by forget-me-not is found in this literature review , the Aquatic Invasive Species Literature conducted by the WIDNR.

1.  Forget-me-not is documented to have a high rate of spread, and is shown to produce abundant seed and can spread through vegetative fragments.  It is also claimed to compete with native plants in wetland habitats but there are no reports cited in the DNR literature review that document forget-me-not outcompeting or crowding out native plants to the point that they are extirpated from a given site.
2. The plant’s ability to escape cultivation is well documented, and its abundance in some situations is also well-known.  But what happens after it escapes and how it impacts ecosystems in which it establishes are less well-known, and no examples of this are cited in the literature that I have reviewed.
3. The effectiveness, and cost/benefits of various control measures are not documented.  The DNR literature review states that some herbicides are non-selective and may  impact non-target species.  And, as the DNR literature review shows, the cost, efficacy, and timeframe of control efforts are “undocumented.”   My experience is that repeated,  hand-pulling, several times a year,  over several years is required to even make a dent in the populations of forget-me-not.
4. To investigate its claims of the potential ecological threats of forget-me-not, the WIDNR used the traditional methods of examining  a variety of variables that constitute what is termed “Damage Potential” in terms of ecosystem impacts.  These potential ecosystem impacts included:

a. Ecosystem Impacts
Composition		Competes with native plants in wet habitats1
Structure		Can alter canopy layer and water flow
Function		May reduce nutrients available to native plants10
Allelopathic Effects		Undocumented
Keystone Species		Undocumented
Ecosystem Engineer		Undocumented
Sustainability		Undocumented

Biodiversity		Undocumented
Biotic Effects		Undocumented
Abiotic Effects		Undocumented
Benefits		Provides shelter and food for macroinvertebrates1

As you can see, the majority of the possible  ecosystem impacts are “undocumented.”

I could find no documented cases–and the WIDNR does not cite any such examples–in which forget-me-not has impacted  the two species in Wisconsin that the WIDNR has said are potentially vulnerable to forget-me-not invasion:  the threatened intermediate spike sedge (Eleolcharis intermedia) and the endangered winged monkey flower (Mimulus alatus).

The most thorough documentation of potential ecosystem impacts comes from the Alaska Center for Conservation Science.  Alaska’s invasive impact assessment can be found here.  And, Alaska’s impact assessment for forget-me-not can be found here.

Conclusion and Recommendations

In brief, the Alaskan report says that forget-me-not has the potential for impacts on community structure, function, and interactions because it can compete with native species in aquatic environments, has the potential to form large monocultures, and has the potential to reduce the populations of native species but, like the WIDNR literature review does not cite any documented cases of these impacts happening.

Forget-me-not also, according to the Alaskan report,  contains alkaloids that are toxic to mammals and can cause weight loss.

But having the potential to cause an ecological impact is a long way from actually causing an ecological impact, let alone such an impact being documented in a scientific case study.

Whether or not these potential impacts are enough to justify calling forget-me-not invasive, let alone warrant the time and expense of a control program, is something that each individual institution and manager will have to decide on their own.

The scarcity of documented ecological impacts of forget-me-not suggest a rich field of research.  Please let me know if you are aware of more recent research that documents actual cases of ecological impacts of forget-me-not.

 

References

Black, M.R. and E. J. Judziewicz.  2008.  Wildflowers of Wisconsin and the Great Lakes Region.  University of Wisconsin Press. Madison, WI.

Czarapata, E. J.  2005.  Invasive Plants of the Upper Midwest.  University of Wisconsin Press. Madison, WI.