Tom's Blog

Sunday, January 24, 2016

Prairie dropseed (Sporobolus heterolepis), an interesting species of high conservation status

There are only a few prairie species in our area with a Coefficient of Conservatism of 10. One of these is prairie dropseed, (Sporobolus heterolepis), an important grass species which is much more prevalent farther west. According to the Atlas of Wisconsin Prairie plants by Cochrane and Iltis, prairie dropseed is an indicator of unplowed and relictual prairies, especially in dry-mesic and mesic sites.

According to the USFS fire effects database, prairie dropseed grows in mesic prairies, well-drained moraines, rock outcrops, glades, open savannas, barrens, lightly grazed pastures, and along railroad and highway rights-of-way. It is considered a climax species that is codominant with little bluestem, big bluestem, and Indian grass.

It is a deep-rooted, long-lived, and drought-tolerant perennial which does well as a ground cover for hot and dry sites. According to Weaver's work in Nebraska, even relatively small dropseed colonies may have roots extending as deep as 4-5 feet into the soil. It is a classic "bunch" grass, and each bunch can remain in place for many years.

Prairie dropseed benefits greatly from fire. According to the USFS fire effects database, fire promotes flowering and seed set. In a Wisconsin study, fire increased flower production by 25 times, vegetative cover by 30 times, and the average plant height by 4 inches.

As befitting a C4 (warm-season) plant, prairie dropseed is only found in open sunlight or at the edge of savannas where full sunlight is still available.

At Pleasant Valley Conservancy there are nine locations where prairie dropseed was remnant, and in addition we have been successful in establishing it from transplants raised from seeds collected on site. In the table below, the original remnant populations were in Unit 1, 2, 3, 3A, 4, 6, 7, 9, and 10. It was planted and is thriving in the Cabin, Pocket, Ridge, and Toby's Prairies, the East Basin Prairie, and Unit 11A savanna. Its presence in the Circle and Triangle might have been either from remnant or planted sources. Left out of this table are the several plants present among the rocks on the East Overlook. Photos of some of these populations are shown below.

Cabin prairie
east basin
Pocket Prairie
ridge prairie
Toby's Prairie
Unit 1
Unit 10
unit 11A
Unit 2
Unit 3
unit 3A
Unit 4
Unit 5
Unit 6
Unit 7
Unit 9

Long-term dropseed population in the upper part of Unit 1, surrounded by little bluestem.
After the first burn in 1997, this population flourished, with extensive seed set.
The seed collected here was used to establish populations in the planted prairies and open savannas

A second remnant population in the lower part of Unit 1, visible from the Quarry trail.

Dropseed establishes well in rocky areas.
This remnant plant has been thriving for a number of years at the lower end of Unit 10 savanna.

There are 8 or 10 dropseed plants growing as remnants among the rocks on the Rocky Overlook (Unit 6).
These plants are best seen in the late fall of the year when their distinct brown color stands out.

In early fall, when the prairie grasses are starting to turn, dropseed can be easily spotted
because it retains its bright green color longer.
This plant in Unit 10 savanna is growing among the dolomite rocks.

Strangely, prairie dropseed is also used extensively in residential and commercial landscape plantings, and for roadside revegetation. In many of the landscape plantings, specially selected "cultivars" are used, such as Tara, Chanticleer, or Winter. Presumably these cultivars have been selected from desirable-looking plants found in natural settings.The photo below shows a typical situation.

In the Madison area, dropseed can often be found growing in special beds near commercial banks, shopping centers, or dividers within parking lots. Some of these populations may even set seed!


Blogger FrankOnABike said...

Back in my first prairie internship, Kane County Forest Preserve district in Illinois, 1997, my supervisor Drew Ulberg had us working on a small gravely prairie kame. On top were some large, gnarled, almost fairy-ring like dropseed patches. He speculated that these plants could have been over 200 years old, and may have been alive to see the first settles pass by in their covered wagons.

Tom, do you have any idea why dropseed establishes so poorly from seed? Its in many commercial prairie seed mix, but rarely do you see it in the resulting plantings.

March 23, 2016 at 11:31 AM  

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