The Slow Death of a “Protected” Prairie-Fen

Before I even begin, I’ll throw out the take-home message. Conservation acquisition and ownership are not enough. Most of our last best places disappear, if they are added to a portfolio of protected lands and left to their own devices.

I visited two such cases today, but I’m going to focus on one, which is known, at least by a few, as the Vernon Prairie-Fen. It’s part of the much larger Vernon Marsh Wildlife Area, which consists largely of low-diversity narrow-leaved cattail marshlands, but here and there are some exceptional fens, particularly around its periphery where calcareous groundwater emerges from below the surrounding uplands.

I wish I had visited it back in 2002, which was the time of the most recent inventory. At that time, notes from the surveying botanist, Larry Leitner, indicate that it was a “complex of calcareous fen, spring, sedge meadow, wet prairie, and shallow marsh.” He further notes that it “has been adversely affected by extensive ditching,” but that it still has “a nice species complement” and is “worthwhile preserving.” The inventory from visits in 2002 and the 1990s includes such goodies as twig-rush (Cladium mariscoides), beaked spike-rush (Eleocharis rostellata, a Wisconsin threatened species), blue-leaved willow (Salix myricoides), sage willow (Salix candida), Ohio goldenrod (Solidago ohioensis), hairy valerian (Valeriana edulis var. ciliata), marsh blazingstar (Liatris spicata) and many others. This site was included in the Southeastern Wisconsin Regional Planning Commission’s Natural Areas and Critical Species Habitat Management Plan as a natural area of county-wide or regional significance, which means there aren’t many natural communities of the same type(s) of higher quality in the area.

Below is a series of aerial images showing the change in extent of the calcareous fen plant community at Vernon Prairie-Fen from 2000 to 2015. The drier areas of the fen, which support more wet prairie vegetation, are lost first. By 2015, the only remaining areas are those that are the wettest and maintain saturation to the surface year-round.


The red line indicates the approximate extent of the calcareous fen plant community in 2000 (approximately 500 feet from left to right). The northwestern-most corner of the fen is a peat mound, and a spring run flows from NNW to SSE across the western portion of the fen. A drainage ditch is visible to the north, which carries water from another spring run that flows down the north side of the peat mound. Shrubs are visible along and north of the ditch (much of which EW likely common and glossy buckthorn) and to the south of the fen (much of this seems to have been willows, as many old, tree-sized Bebb’s willows are still present there today).


In 2005 glossy and common buckthorn are advancing from the north and east, and relatively open fen only remains inside the dark orange line. Left to right is about 350 feet.


The advance of buckthorn continues in 2010, and the fen is reduced to the area inside the light orange line. Left to right is about 225 feet


An additional bit at the east end of the remaining fen had been lost by 2015. Left to right is about 160 feet.  It isn’t obvious here, but narrow-leaved cattails, which occupy open areas just to the south and west, are also encroaching from that direction, so about a third of the remaining area is co-dominated by narrow-leaved cattail.

Here are some photos I took today.


This is a look at some of the vegetation matrix. Present here are swamp thistle (Cirsium muticum), Ohio goldenrod (Solidago ohioensis), Canada bluejoint grass (Calamagrostis canadensis), chairmakers rush (Schoenoplectus pungens), and marsh fern (Thelypteris palustris) among other things…including more glossy buckthorn (Frangula alnus).

VPFen Cladium

Twig-rush (Cladium mariscoides), which is actually a sedge was still present in a small area. This species is restricted to our best calcareous sites in SE Wisconsin.


Blue-leaf willow (Salix myricoides) also tends to be associated with high quality calcareous sites in SE Wisconsin, and it is among my favorite willows.

beaked spikerush

The tangly stuff seen here growing over and obscuring the spring run coming off the peat mound is beaked spike-rush (Eleocharis rostellata, threatened), which is also not a rush, but a sedge. Also visible is hardstem bulrush (Schoenoplectus acutus), which is also a sedge, and more glossy buckthorn.



Most of what was formerly part of the fen plant community looks like this today…a solid thicket of mostly glossy buckthorn.

None of this was particularly surprising, even if it still almost brought me to tears. I visited, because I had looked at the air photos, and I’ve seen enough of those to know what a wetland swallowed up by buckthorn looks like. I was heartened to still find a few real gems after crashing through the thicket.

I know that within the same project area resources are going into reconstructing communities in places where they have been previously completely or nearly completely destroyed, so why are these irreplaceable resources being allowed to fade away, particularly publicly-owned places that are supposedly protected?  That’s rhetorical. There are limitations on how money can be spent. There are other priorities in wildlife areas. Most in the public don’t notice when a fen becomes a buckthorn thicket. There may even be a lack of awareness of what is there among professionals as staff turn over.

Maybe twig rush and blue-leaved willow don’t get people very excited. What about pickerel frogs, or the swamp metalmark butterflies that rely on swamp thistle?

All I know is that we need stewardship, because our last best places are blinking out all over SE Wisconsin, and a lot of this is happening on lands that were acquired for protection. DEVELOPMENT IS NOT THE GREATEST THREAT TO REMNANT NATURAL COMMUNITIES. IT IS LACK OF STEWARDSHIP. Yes, that was me yelling.



About prairiebotanist
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5 Responses to The Slow Death of a “Protected” Prairie-Fen

  1. benlikesjazz says:

    Fiends of Vernon Marsh would rather have a wine tasting picnic with their WEAL and WCLC pals than invest in the Marsh.  Or so I believe.

  2. Mariette Nowak says:

    Hi Dan,

    I believe I know the fen you are talking about if it’s located off a trail from the Highway ES parking lot. I visited the fen, years ago, led by Ron Kurowski. when it was much more beautiful and less invaded by buckthorn and have visited on my own occasionally since then. Last year when I visited it was the worst. Have you contacted the DNR regarding the fen? I hope something can be done to revive it. All the best,



    • I know which fen you are talking about. This is a different one. It is to the north on the other side of the marsh. Really, most high quality DNR-owned properties that do not have state natural area (SNA) designation in SE Wisconsin are in severe decline. I haven’t spoken to the WDNR about this one specifically, but I have about others. That said, there isn’t much reason to even bother right now, because SNA staff pretty much stick to SNA properties, and the WDNR simply isn’t staffed and resourced to care for non-SNA property beyond infrastructure and wasting effort on brush work that isn’t followed up with stump treatment or burning intermittently and often in areas of questionable relative ecological significance.

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