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

Circle

east basin

Pocket Prairie

ridge prairie

Toby's Prairie

triangle

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!

Floristic Quality Assessment at Pleasant Valley Conservancy Based on 13 years of Data

The Floristic Quality Index (FQI) has become a widely used measurement of natural areas quality. This standardized tool was developed by Floyd Swink and Gerould Wilhelm at the Morton Arboretum, and is explained in detail in their book: “Plants of the Chicago Region”, published by the Indiana Academy of Sciences. FQI is not a stand-alone value, but is  used together with other assessments to evaluate the quality of a site.

Measuring the FQI begins with an assemblage of a complete species list for the site. Each species is assigned a unique Coefficient of Conservatism (a number from 0 to 10), which expresses the probability that this plant species is likely to occur in landscapes relatively unaltered from those of pre-settlement times. Plant species with high C values are relatively specialized in their requirements, and are thus found in more restricted habitats.

C values are assigned to species on a state-wide basis, and the C values for Wisconsin plants can be found in an extensive publication edited by Thomas Bernthal issued by the Department of Natural Resources.

FQI is calculated by multiplying the mean C value for a site by the square root of the number of species at that site. (As far as I can determine, Swink and Wilhelm have not explained the basis for this formula. Why, for instance, square root of number of species?)

Since 2002 I have been keeping detailed records of plant species at Pleasant Valley Conservancy. This year Amanda brought together all data from 2002 through 2015 (13  years), sorted them by management unit, and then applied the C values and made the FQI calculation for each unit. The table below provides the data, sorted by FQI (highest on top). Also given in the table is the acreage and total number of species for each unit, and a brief description of its ecological character. The location of each unit can be found in the Management Map found at this link.

The single highest FQI was in Unit 6, an outstanding hill prairie/savanna. This unit is a large remnant with a bur oak savanna above and in the gullies and dry mesic prairie on the lower slopes. Before restoration had begun this unit, although fairly degraded, had a well developed tallgrass prairie flora with a big bluestem remnant at the top under the rocks and little bluestem on the lower slope, and two moderately sized Indian grass patches.

Also, high FQI values were found in Unit 11A, Unit 10, and Unit 12A, all of which are well-restored oak savannas.

Other units with high FQI values were three of the older and larger planted prairies (Toby’s, Valley, Pocket) and four of the larger savanna areas (Units 5, 8, and 12B.

Other high FQI values were found in the larger units (not surprising, because the larger units in general had more species).

The rest of the data for units at PVC, all with FQI values over 30, are given in the table below.

Name	FQI	Acreage	Total species	Present status
Unit 6	63	4.48	153	Upper (Bur oak savanna) Lower (Prairie remnant)
Unit 11A	61	5.17	119	Prairie remnant and bur oak savana
Toby's Prairie	61	3.63	126	Dry-mesic prairie (partially remnant; mostly planted)
Unit 10	60	2.9	136	Bur oak savanna
Unit 12A	59	5.95	138	White oak savanna
Valley Prairie	58	3.85	130	Dry, mesic, and wet-mesic prairie (planted)
Pocket Prairie	57	4.5	104	Dry, mesic, and wet-mesic prairie (planted)
Unit 7	56	1.58	117	Upper (Bur oak savanna) Lower (Prairie remnant)
Unit 3	56	1.03	105	Prairie remnant
Crane Prairie	55	2.6	130	Dry, dry-mesic, and mesic prairie (planted)
Unit 8	54	1.3	102	Bur oak savanna
Unit 12B	54	0.98	114	White oak savanna
Unit 5	52.5	1.61	105	Bur oak savanna
Unit 2	52	1.6	89	Prairie remnant
East Basin	51.5	4.4	100	Dry-mesic, mesic, and wet-mesic prairie (planted)
Ridge Prairie	51	1.67	100	Dry-mesic prairie (planted)
Unit 23	51	0.38	93	Bur oak savanna
Unit 19C	48	1.13	71	Black/bur oak savanna
Unit 21	47	3.38	75	White oak woodland
Triangle	47	0.55	81	Hill's oak savanna
Unit 20 combined	46	3.35	86	Woods and prairie mix
Barn	46	0.48	87	Wet mesic prairie (planted)
Unit 9	45	1.82	82	Bur oak savanna
Cabin Prairie	45	0.54	83	Mesic prairie (planted)
Unit 1	44	1.18	61	Prairie remnant
Unit 11D	43	4	74	White oak savanna
Unit 4	41	0.32	48	Prairie remnant
Unit 19A	40.8	0.33	69	Bur oak savanna
Unit 19B	38	1.64	51	Bur oak savanna
Unit 19D	35	1.05	30	Bur oak/black oak savanna
Unit 19E	34	1.47	37	White oak savana

Amanda also made the FQI calculations for Pleasant Valley Conservancy has a whole. There were 335 total species, the average C value was 5.1, and the FQI for the whole Conservancy was 93.21. (This number is much higher than that of any single unit, reflecting the importance of species number in the FQI calculation.)

Another interesting analysis is that of the various planted prairies at PVC. The table below shows, not surprisingly, that the older planted prairies have higher FQIs than the younger ones.

Name	FQI	Size (acres)	Year planted	Age in 2016
Toby’s	61	3.63	1998	18
Pocket Prairie	57	4.5	1999	17
Valley Prairie	58	3.85	2002	14
Barn Prairie	46	0.48	2002	14
Cabin Prairie	45	0.54	2002	14
Crane Prairie	55	2.6	2005	11
Ridge Prairie	51	1.67	2005	11
East Basin	51.5	4.4	2009	7