Tom's Blog

Monday, June 23, 2008

Visit to savanna near Rush Creek State Natural Area

Yesterday Kathie and I toured an interesting private savanna site near Rush Creek State Natural Area. This SNA is part of the blufflands on the Mississippi River. The tour was lead by Armund Bartz, a DNR Conservation Biologist who works out of the La Crosse office.

Rush Creek is a large State Natural Area with imposing high prairie bluffs facing the Mississippi River. The site we toured was a private site contiguous with Rush Creek that the landowner has been restoring for the past ten years. Although small (less than 50 acres) this was a high quality site with open-oak woodlands and some open-grown oaks on the high bluff. It has a very diverse understory of savanna and woodland species, including two that I was particularly interested in seeing, upland boneset (Eupatorium sessilifolium) and purple milkweed (Asclepias purpurascens).

These are two species that we have been especially studying at Pleasant Valley Conservancy. Purple milkweed is an endangered species that is found only in the southern part of Wisconsin. Although we have quite a few plants at Pleasant Valley Conservancy, scattered across our savannas, the habitat they require, deep-soil sites with dappled shade, is not common these days. Since I have been doing research on the conservation of this species, I try to visit any site where it is present. The site we visited yesterday had several fine populations, with a lot of plants in full bloom. They looked identical to ours. However, unless they are flowering, positive identification is uncertain, as they can be confused with common milkweed, Asclepias syriaca. In fact, there is some thought that these two species might hybridize, although there is no experimental data to support this.

Upland boneset is a Special Concern species in Wisconsin. It is another species that requires open-shade sites, such as open oak woods or savannas. It is also found only in southern Wisconsin and has a very high coefficient of conservatism (9). At Pleasant Valley Conservancy we initially had only a single patch, and have been working to establish it in other sites. We have had poor success planting seed, probably because seed viability is low. So we have been raising plants in the greenhouse (from the few seeds we have been able to get to germinate) and transplanting them to suitable sites on the Conservancy. We have had good success with transplants, but so far no evidence of spread.

The Rush Creek savanna, on the other hand, has lots of this species, growing in many sites across the steep hillside. It took a bit of experience to spot them, however, since woodland sunflower plants were widespread and superficially look similar. However, upland boneset has a distinctive sessile leaf structure that cannot be mistaken for anything else (see photo here). It was too early to see flowers.

After touring through the savanna areas we came onto a dry rocky prairie, the type that is so characteristic of the Mississippi River bluffs. There we saw the usual array of dry-prairie species, such as short green milkweed, lead plant, little blue stem, silky aster, bird's foot violet, etc. This very steep south-facing slope was a challenge to surmount, but when we reached the top we had a fine distant view of the River. The vertical elevation here is over 400 feet. Those with better ears than mine heard a cerulean warbler, a species that breeds mainly where there are large areas of woods.

The Rush Creek field trip was really enjoyable. The participants were knowledgeable and interested, and the leader knew the site very well. In all, a great day, and well worth the 2.5 hour drive from Madison!


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