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.

VPFen2000

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).

VPFen2005

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.

VPFen2010

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

VPFen2015

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.

VPFen1

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.

VPFenSalixMyricoides

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.

 

VPFenbuckthorn

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.

 

 

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Posted in biodiversity, Conservation, Fens, invasive species, native plants, Prairie, Stewardship, wetlands | Tagged , , , , , , , , , , | 5 Comments

Sprucing up Army Corps Wetland Plant Indicators (Update)

Apparently the Army Corps has plowed ahead with its deeply flawed analysis of herbarium records. They posted a document called “Clarifying the Use of Herbaria Records for the NWPL 2018 Update.” However, this document does not even acknowedge the problem I raised, which is that even a plant for which only a third of herbarium records are from wetlands still has far more wetland records that one would expect by chance, because far less than a third of the landscape (more like 10%) is wetland. Rather, such a plant is better described as being over 3X more likely to occur in a wetland sample plot than an upland sample plot. Apparently Army Corps botanists aren’t really rocking what is some very fundamental and basic ecological sampling and inference. These are career folks. Of course they couldn’t possibly be wrong. Here is link to the panel members’ emails, which are published online.

 

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Sprucing up Army Corps Wetland Plant Indicators

Last week, I decided to check out the Army Corps website to see if they have updated their wetland plant list for 2018. There, I found a link to a presentation that sets forth an approach for a major revamping of wetland indicator statuses. http://wetland-plants.usace.army.mil/nwpl_static/home/home.html

They are proposing using annotated herbarium data to get a more objective idea of species affinities for wetland versus non-wetlands sites. Huzzah! I like plants. I like numbers. I like the idea.

However, as I watched the presentation, a HUGE problem became obvious. To explain, I have to take a step back and talk about wetland indicator statuses. For each species, these are supposed to describe the fidelity to wetland conditions. In the past, these were associated with numerical values, but they have been more recently been revised to be more qualitative.

It turns out that the Army Corps is proposing to rely heavily on a study that focused on blue spruce in Colorado. In that study, they determined the percentage occurrence of blue spruce in the field, compared it to the “old school” indicator numerical values, and drew a conclusion.

In that study , wetland delineation indicators are used around a plot-based rather than a plant-based approach. FAC plants are roughly equally likely (34-66%) to occur on wetland sample plots vs. non-wetland plots (they have no affinity for wet vs. not). If this concept is detached from the plots and applied to individual plants on a landscape, it is biased by the proportion of land that is wetland vs. upland. In other words, the percentage value you determine by investigating individual plants and whether or not they are growing in a wetland (like the spruce) becomes a direct function of the percentage of the landscape that is wetland, which disconnects the observation from the biology of the plant.

I use pooled data (numbers of trees in wetlands and non-wetlands) from the study (paywalled, so I had to request a copy) and tested a null hypothesis that blue spruce is borderline facultative (34% of occurrences expected in wetland sample plots), given several possible values for landscape wetland coverage. I had to guess at these, because I don’t have a value for landscape wetland percentage for your study area.

bluesprucefigure1

Figure 1. This illustrates the effect that changing wetland proportion on the landscape would have on observed percentages of a borderline FAC (34%) species. Only when wetlands and non-wetlands are equally represented is one likely to encounter individual plants in wetlands 34% of the time and in non-wetlands 66% of the time. However, the chance of occurrence in a sample plot placed in non-wetland and the chance of occurrence in wetland plot (fixed effort) will remain the same across this gradient. The borderline species is always just under twice as likely to be found in an upland plot compared to a wetland plot. Viewed this way, the indicator status maintains its biological meaning across landscapes varying in wetland extent. It loses biological meaning otherwise.

Figure 1 illustrates how the percentage of plants observed in wetland for a borderline FAC species varies depending on the percentage of the landscape that is wetland. Looking at this, keep in mind that Colorado wetland extent is ~2% (the study was mostly in Colorado) and Lower 48 wetland extent is ~5%. If half of the landscape is wetland, you expect 34% of occurrences to be in wetland and the rest to be in non-wetland. However, as the proportion of wetland on the landscape gets smaller and smaller, you expect to encounter a smaller and smaller proportion of species occurrences in wetland. This is independent of biology and occurs as an artifact of landscape wetland/non-wetland composition. This is because the number of plants distributed relatively sparsely in uplands overwhelms the numbers occurring relatively densely in wetlands as wetlands become rare. Even as the percentage/proportion of plants in wetlands decreases with the wetlands on the landscape, the chance of finding the species in any single upland plot and any single wetland plot (standard effort) does not change! So surely our spatial interpretation of indicator statuses must be tied plots or units of standardized effort, if we want them to have any biological/ecological meaning.

There is a way to estimate a landscape percentage or proportion of species occurrences and roll those into a useful analysis.  However, if that is the most practical approach, we need to take one more step to determine whether or not we’re seeing a species in wetland more or less than is expected. We can test our observed proportion against expected proportions, which can be calculated to take into account the landscape cover of wetlands (Table 1). This is the simplest case of such a test of whether observed values equal expected values, so an appropriate test would be a binomial exact test (a chi-square test is also appropriate, if expected values aren’t too small, but in this case they are, so I went with the binomial test…inference is the same).

bluesprucetables

Table 1. Expected proportions of wetland occurrence (right column) are given for a borderline FAC species for different levels of landscape wetland coverage. On average, Colorado is 2% wetland and the Lower 48 is 5% wetland.

Figure 2 is a simple bar graph with the estimated proportion of spruce in wetlands with 95% confidence intervals based on the binomial exact test.  Horizontal lines from bottom to top are expected proportions in wetlands for a borderline FAC (34%) species for 2% landscape coverage of wetlands (Colorado) on up 30% (in case the study area is 6 times as wet as the lower 48 as a whole). As you can see, unless the landscape coverage of wetlands is something more than 30%, the data aren’t significantly different from what you would expect from a borderline FAC species, and if the wetland coverage is more in line with Colorado or the lower 48, the study actually observed many times more trees in wetlands than would have expected by chance. In other words, if you went out in the field and established a wetland sample plot (vs. hunting for trees), you would be much more likely to see blue spruce than you would if you established an upland sample plot. Or to put it another way, there is a significant affinity between blue spruce and wetland site conditions.

bluesprucefigure2

Figure 2. Gage et al. estimated proportion blue spruce in wetlands with 95% confidence interval from binomial exact test with horizontal lines representing expected proportions for a borderline FAC species in landscapes that vary in percentage wetland (for 10% wetland the probability that the observed value did not differ from the predicted value was essentially 0, or 2.2×10^-16.)

If wetland covers 30% of the landscape, then the observed proportion of blue spruce in wetland is not significantly different from what would be expected from a borderline FAC (34%) species.

If you want to take this to the extreme, all you have to do imagine a landscape like that of the lower 48 (5%) wetland. A species that occurs in 100% of wetland samples and in only 10% of upland samples would be expected to be encountered on the whole landscape 66% of the time in uplands and 34% of the time in wetlands! It’s worth reiterating, we must either compare percentages when effort is equal between wetland and uplands or adjust our expected values based on landscape wetland coverage.

Botanists can do math. Right?

 

 

 

 

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