Establishment of compass plant (Silphium laciniatum) in prairie and savanna habitats

Compass plant (Silphium laciniatum), an icon of the tall grass prairie, is one of the first prairie species to disappear upon grazing (see Curtis quote at the end of this post). At Pleasant Valley Conservancy it was completely absent from the unrestored prairie remnants, even though many other prairie species (including such conservative species as Amorpha canescens; Sporobolus heterolepis; and Ceanothus americanus) were still present.

When restoration began, compass plant was high on our priority list for reintroduction and it has been in all of our seed mixes for planting on all prairie or open savanana sites after they had been cleared and burned. However, it is slow to develop, and the first year all one usually sees is a single leaf. It continues to grow only vegetatively for the first few years, just making a large tap root. Although in favorable garden-like settings it can flower the second or third year after planting from seed, in most prairie restorations it takes at least five or six years to flower.

The first plantings at PVC were on November 1998 at the former ag field (future Toby’s Prairie) and at the recently cleared Overlook area (Unit 5A) on the South Slope. The Overlook area was planted again in April 1999 after burning. The first flowering plant at Toby’s Prairie was in 2004, six years later, but flowers were not seen at the Overlook until 2007 (nine years later).

The Overlook has the appearance of a severe habitat, highly exposed, with a rocky soil and intense solar radiation. Despite this, flowering compass plants have continued to be present at the Overlook since it was first restored. In 2018 there were three tall flowering plants.

As the table shows, we have been successful in getting compass plants established from seed at a wide variety of sites. It is now widespread at Pleasant Valley Conservancy, in various kinds of prairies as well as open savannas.

Compass plants from seed to first flowering

Year planted	First Year flowered	Location	Habitat	Years to flowering
2002	2006	Barn	Wet mesic prairie	4
2002	2008	Cabin	Dry mesic prairie	6
2005	2007	Crane	Wet mesic prairie	2
2003	2014	Unit 11A	Open savanna	11
1999	2004	Pocket	Mesic prairie	5
2005	2010	Ridge	Dry mesic prairie	5
1998	2004	Toby’s	Dry/Dry mesic prairie	6
1998	2016	Unit 5A	Dry prairie	9
2003	2008	Unit 11A	Open savanna	5
2004	2009	Unit 11D	Open savanna	5
2002	2006	Unit 12A	Open savanna	4
1999	2005	Unit 18	Dry mesic prairie	6
2002	2012	Unit 19B	Open savanna	10
2002	2008	Unit 19C	Open savanna	6
1999	2009	Unit 2	Dry prairie	7
2004	2014	Unit 2 PV Road cut	Dry prairie	10
1999	2008	Unit 3	Dry prairie	9
1999	2008	Unit 3A	Dry prairie	9
2001	2006	Unit 6	Dry mesic prairie	5
2002	2008	Unit 7	Dry mesic prairie	6
2002	2008	Valley	Wet mesic prairie	6

Average years to flower: 6.5

Total sites: 21

South Slope with scattered compass plants

Tall compass plant on the steep road bank. This is one of the driest parts of the site.

Top of the South Slope by the Far Overlook.
In addition to compass plant, little bluestem, pale purple coneflower and bur oak grubs and saplings

Now that compass plant is so well established, how long will it continue to thrive?

The work of Frank Gould, one of Norman Fassetts students at UW-Madison, is pertinent. In 1936 Gould did an extensive survey of prairie remnants of Dane County, using the original surveyor’s prairie map as a guide. Although most of the original prairie was gone, he found remnants of it along roadsides, railroad tracks, “little-used pasture land”, and “wastelands”.

Among other species, he recorded the presence of Silphium laciniatum in 156 localities, of which 150 “are within the bounds of the original prairie districts as outlined on the old [original surveyor’s] map.” See Gould’s map below.

From Gould, Frank W. 1937. The present status of Dane County prairie flora. M.A. thesis, University of Wisconsin-Madison. See also Gould, Frank W. 1941. Plant indicators of original Wisconsin prairies. Ecology Volume 22: 427-429.

The largest prairie area on Gould’s map is that north of Lake Mendota that was once known as the Empire Prairie. The outlines of this part of Gould’s map follow almost exactly my Empire Map done by GIS that was alsobased on the original surveyor’s map.  It seems evident that compass plant has continued to thrive in the prairie areas where it had been present in 1836, when the original surveying was done.

Thus, I conclude that as long as suitable remnant prairie habitat remains, compass plant will continue to thrive, but it is not able to move onto “new” ground, as so many other of the prairie plants are able to do. It especially suffers severely from grazing.

The South Slope bluff prairie is an interesting compass plant habitat. How can compass plant, a conservative mesic species with a “C” value of 8, do so well in this sort of habitat?

Scanning the South Slope recently, I saw a compass plant 5 feet tall in the middle of what should have been the driest area. I looked further and saw a few more, almost as tall. I started counting and found at least two dozen compass plants, all in flower, and all looking very healthy, scattered across the slope.

In retrospect, I should not have been surprised. When the NRCS Site Description team visited PVC in 2014, they showed me that the soil on our “rocky” slope was very deep. They were able to thrust a 7 foot long metal probe all the way to the hilt. This type of soil is called colluvium. Although its surface is about 1/3 rock, the rest is exposed loamy soil quite suitable for deep-rooted prairie plants. 

If you want to see these bluff prairie plants, take a walk along the South Slope on Pleasant Valley Road from the driveway to County F.

Here is the passage from Curtis on grazing: (Vegetation of Wisconsin 1959; page 426)

 “Prairies on wet-mesic, mesic, and dry-mesic sites are literally wiped out by grazing, sometimes with almost unbelieveable rapidity. About 1940, a large tract of virgin wet-mesic prairie adjacent to the Faville Prairie Preserve of the University of Wisconsin Arboretum, in Jefferson County, changed ownership and was subjected to heavy grazing under cattle and horses by the new management. During the first summer, the animals proceeded to attack the species of highest palatability, with the very abundant plants of Silphium terebinthinaceum and S. laciniatum sought out like hidden candy at a child's birthday party. By the end of the second year, no prairie species whatever were visible in the closely cropped sward, although many were no doubt present as underground roots or rhizomes. The obvious dominants were redtop grass (Agrostis stolonifera) and Kentucky bluegrass (Poa pratensis). Other portions of the same prairie which had been pastured for a number of years were dominated by the bluegrass, with lesser amounts of redtop and quackgrass, plus an occasional native plant of ironweed, sneezeweed, common milkweed, and high populations of the exotic dandelion, Canada thistle, and white clover. No traces of the prairie grasses originally present nor most of the prairie forbs were to be seen. This total destruction of the original prairie dominants by grazing is to be explained by comparing their growth habits with those of the invading exotics. The native grasses produce erect growing points which are clipped off by the cattle (Neiland and Curtis, 1956). The exotic species like bluegrass, however, have creeping rhizomes which send up individual leaves. Removal of the tips of the leaves causes no permanent harm, since the tissues are replaced by the meristematic region at the base of the leaf. The exotics thus have a tremendous advantage in the competition for space.”