Saturday, August 16, 2014

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.

(1) Eubanks, M. 2001.  The origin of maize: evidence of Tripsacum ancestory. Plant Breeders Reviews
(3) Anderson, R.C.  1985. Aspects of the germination ecology and biomass production of Eastern Gamagrass (Tripsacum dactyloides). Botanical Gazette 146.
(4) &newsletterid=1730)
(5) see
(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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