Prairie Flora in North Carolina: Eastern Gamagrass

Tall culms of Eastern Gamagrass in a "Piedmont Prairie" in central NC
with Daniel Overcash & Louis Suther

Eastern Gamagrass (Tripsacum dactyloides) is one of North Carolina's tallest and most robust native grasses.  A clump forming, warm season, perennial, with flowering culms that can reach 7-8' in height, the species responds well to fire and thrives in open sunny, yet somewhat moist sites.

Flowering Tripsacum dactyloides with pistillate (below)
and staminate flowers (above)

Tripsacum is monoceious, producing both male (staminate) and female (pistillate) flowers on an individual inflorescence.

Tripsacum is perhaps one of the most ecologically and agriculturally important native genera from North America. Widespread throughout the eastern US, Mexico, & parts of S. America, Tripsacum was a key ancestor of modern day corn (1) and could eventually contribute to agricultural sustainability efforts focused on perennial rather than annual crops.  At least one cultivar has been developed between Gamagrass and Zea mays that may be a step in that direction (2)

Tripsacum patch expanding in old field at Manassas Battlefield, VA

It produces significant live, leafy biomass with high live - dead ratio and is highly palatable for many grazers. Because of this excellent forage quality, Gamagrass is a classic "decreaser" in range management terminology; when present, grazers actively and preferentially seek it out and cause it to decline under sustained pressure.

Tripsacum dactyloides cupule with persistent pistillate flowers

In mid-summer, large seeds develop and ripen progressively from the top, eventually disarticulating when ripe (see image, right). Due to their size, they have little chance of dispersing far from the mother plant. Under intense grazing pressure or declines due to other factors, it is easy to understand why Gamagrass would be slow to recolonize. Heavy seed predation by rodents may also be a limiting factor in spread (3).

Individual seeds are enclosed in a hardened case sometimes called a "cupule". When intact, this structure can inhibit germination of the enclosed seeds (3)

Tripsacum dactyloides cupules on mineral soil 

Large clumps of Gama tend to develop a characteristic "hollow" in the middle of an almost circular ring of leaves.  As the clump develops upright stems, a tent of sorts forms over the nearly bare middle, providing nesting habitat for a number of ground nesting birds associated with prairies (4). Many such birds are among the most declining in the Piedmont region.

Tripsacum clump developing concentric ring,
 beneficial to some ground nesting wildlife

Herb Amyx, Joan Schnier, John Thomas, Jon Stucky
observing a riverside patch of Tripsacum

As suggested by its relatively wide natural range, Gamagrass is adaptable to a host of conditions. In part, this is due to extensive aerenchyma  root tissue (essentially air passages) that allow it to thrive in wet or even infrequently flooded situations (see image, left).

In addition, the roots are able to penetrate restrictive soils (including claypans) and survive droughts and other limitations that other species can not (5).






Consequently, Eastern Gamagrass can be an important member of a number of natural community types. These include certain blackland prairies in Texas (5), and coastal prairies in Louisiana and Texas (6). I have also observed Gama as locally abundant or dominant in longleaf pine woodlands in eastern Texas and other remnant, prairie-like communities in southeast Texas. In North Carolina, Tripsacum is an important member of what may be North Carolina's only remaining prairie, and is becoming locally abundant in several frequently burned areas elsewhere in the Piedmont providing clues to other habitats it may have occurred in.

Gamagrass clumps in an open woodland in which prescribed fire has been used twice
Durham Co, NC

Although Tripsacum dactyloides appears to be indicative of prairie-like habitats across North Carolina, and perhaps through its natural range, I hesitate to suggest "introducing" it to natural areas without first applying regular prescribed fire (and having the means to continue to do so), obtaining open habitat structure, removing invasive plants, and having a pretty good indication it may have been present historically.  Having said that, not every "restoration" of such habitats needs Gamagrass or likely ever had it. I prefer allowing even like sites to have their own unique floristic assemblages.

References:
(1) Eubanks, M. 2001.  The origin of maize: evidence of Tripsacum ancestory. Plant Breeders Reviews
(2) http://www.google.com/patents/US20140123357
(3) Anderson, R.C.  1985. Aspects of the germination ecology and biomass production of Eastern Gamagrass (Tripsacum dactyloides). Botanical Gazette 146.
(4) http://www.houstonaudubon.org/default.aspx?act=newsletter.aspx&category=Natives &newsletterid=1730)
(5) see http://link.springer.com/article/10.1023/A:1004256100631#page-1
(6) http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC04/reference/econatres.napc04.ocollins
(7) Diamond, D. D. & F. E. Smeins. 1984. Remnant Grassland Vegetation and Ecological Affinities of the Upper Coastal Prairie of Texas. Southwestern Naturalist 29.

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Ascending the Slippery Slope of Restoration

For several years now, I and the NC Plant Conservation Program have been working with the Eno River Association to restore their oldest Nature Preserve, the Blue Indigo Slopes.  The site is important, in part, due to the rare plants present as well as frontage on the Eno River . In addition, we view it as an important stepping stone in a landscape-level pollinator pathway in northern Durham (perhaps I will explain what that is in a future post).

During a routine visit this year, late in June, I noted general ecological conditions of the site and recorded mental notes on additional ecological restoration needs. A few observations follow:

Flowering Spurge (Euphorbia corollata)
widespread in eastern U.S.
often found in open sites or prairies
a few stems flowering here and there on the Slopes in esp. open areas

Piedmont Barbara's Buttons (Marshallia obovata)
locally abundant in some of our open, burned sites; this specimen
was flowering much later than typical for the species in our area
a small colony is present on the site

Post Oak (Quercus stellata) and Blackjack Oak (Quercus marilandica) sprouts and seedlings were apparent around the open edges of the site (see below). I think of these two oaks as likely historically important in many Piedmont open woodlands and savannas; both tolerate fire well. However, Blackjack is especially intolerant of shade and may be easily overwhelmed by faster growing, shade tolerant species - a major reason it is rarely seen today in the region.

Top: Blackjack Oak (Quercus marilandica) sapling amidst prairie flora
Bottom: Post Oak (Quercus stellata) sapling near clumps of Eastern Gamma Grass

Like many other rare plant sites in the Piedmont, this site was historically more open & prairie-like. A common attribute of these sites is the tendency to become heavily overgrown by dense trees and shrubs, presumably due to the absence of fire or grazing. One result of this change is the decline of  many understory species that are now of conservation concern and require special efforts to restore their populations.

We have begun an ecological restoration program supported by the Eno River Association Board, staff, and volunteers. Part of the restoration has involved slowly removing trees (mostly Loblolly Pine) and other invading brush from the site. As part of the broader effort we also conducted two consecutive spring-time prescribed burns on the Preserve. 

Results are becoming apparent!

The images above show a portion of the site before and after preliminary ecological restoration 

(November 2007 & February 2013); 

Note the large, limby eastern red cedar on the right side of both images

The green "clump" in the middle of the 2013 image is a shortleaf pine sprouting after fire

images complements of Kurt Schlimme of the Eno River Association.

The site's namesake, Wild Blue Indigo (Baptisia australis var. aberrans), suffered for years under the growing canopy. A decent number of individuals are still present but most are relatively small and still show diminished flowering. Consequently, very few of the individuals actually produce fruit. The individual shown below has only a single pod this season and appears to be affected by powdery mildew or some other pathogen. Although I don't know the identity of the white substance illustrated below we did document powdery mildew on these plants several years and a pathologist suggested heavy shade and associated moist conditions were contributing factors. We have purposely "gone slow" on the canopy re-opening, but the continued relatively poor vigor and possible mildew problems on the Wild Blue Indigo suggest we need to renew and expand our efforts. 

Newly developing Prairie Wild Blue Indigo Pod (Baptisia australis var. aberrans)
Typical "healthy" plants produce numerous pods, this is the lone pod on this individual

The site supports a scattered population of Starry Rosinweed (Silphium astericus) (left below) just coming into flower, as well as numerous Glade Wild Quinine (Parthenium auriculatum) (right below). As with the Blue Indigo, relatively few of the Glade Wild Quinine appear likely to flower this year.

An open prairie-like portion of the Eno River Association's Indigo Slopes Preserve (above). A Post Oak sapling can be seen near the back of the opening near the large pines, a Prairie Wild Blue Indigo individual occurs on the right, and scattered rosettes of Glade Wild Quinine (Parthenium auriculatum) can be seen throughout. The extent of the opening is less than 1/4 acre and surrounded by dense woods on at least 3 sides. We hope to significantly expand this opening, both up and downslope, in the near future.

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