Schwinning Lab

Plant Ecology

Yang Tse

Invasive grasses

KR bluestem

Yellow bluestem forms nearly monocultures on Texas rangelands
Johnsongrass seedling

A Johnsongrass seedling grows faster than the seedlings of many native grasses our research showed

The invasion of American grasslands by exotic grasses is a challenge to grassland management, but also raises fascinating questions in plant community ecology: Why is it that some grass species introduced from Europe, Asia or Africa have been so exceptionally successful in North America? At the surface, there seems to be nothing special about the newcomers that would explain their apparent competitive advantage over native species. Over the years, students in the Ecology Lab have examined both mechanims of invasive success and methods for the control of established invasive species in central Texas grasslands.

In collaboration with Dr. Philip Fay at USDA/ARS (Temple, TX), and through funding from USDA, we have conducted greenhouse and field experiments to examine when and how the invasive species Johnsongrass (Sorghum halepense) begins to establish competitive dominance over native species and which traits might be involed. Former graduate student Heather Meckel and current graduate student Alexandra Salinas found that, above all, Johnsongrass tillers develop much faster than those of native species, whether establishing from seed or rhizome buds. Johnsongrass tillers can overtop almost any native grass species within a week or two of emergence. Adding to its success is the species' nitrogen use efficiency, although it is not higher than that of some native species.

The spread of yellow (KR) bluestem (Bothriochloa ischaemum) in Texas is just one example of an invasive grass all but replacing a diverse native grass flora after introduction. We have conducted experiments to quantify the potential allelochemical effect of KR bluestem on native and recentlly arrived invasive species such as silky bluestem (Dicanthium sericeum). In contrast to earlier reports, we found no evidence of allelochemical suppression of competitors by yellow bluestem.

On the issue of combating invasive grasses in the field, we have collaborated with Dr. Kelly Lyons at Trinity University in San Antonio. In this work, we focussed on determining prescribed fire regimes more detrimental to invasive species than to native species. Former graduate students Erin Ruckman and Scott Havill determined that prescibed fire in a drought year or in summer is potentially more damaging to KR bluestem than to native species, which have likely adapted to the combination of drought and fire in semi-arid American grasslands.

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Schwinning, S., Meckel, H., Reichmann, L.G., Polley, H.W., Fay, P.A. 2017. Accelerated development in Johnsongrass seedlings (Sorghum halepense) suppresses the growth of native grasses through size-asymmetric competition. PLOS ONE 12, 20176042 pdf

Reichmann, L.G., Schwinning, S., Polley, H.W,, Fay, P.A. 2015. Traits of an invasive grass conferring an early growth advantage over native grasses. Journal of Plant Ecology DOI:10.1093/jpe/rtw014 pdf

Havill, S. Schwinning, S., Lyons, K.G. 2015. Fire effects on invasive and native warm-season grass species in a North American grassland at a time of extreme drought. Applied Vegetation Science 18:637-649 pdf

Ruckman, E., Robinson, T., Lyons, K.G., Schwinning, S. 2012. Comparative seed heat tolerances among native and a non-indigenous, invasive species: implications for selective management of grassland using fire. Ecological Restoration 30: 136 – 142. pdf

Ruckman, E., Schwinning, S., Lyons, K. 2011. Rainfall - burn time interactions in the recovery of an invasive grass after prescribed burn. Restoration Ecology 20: 756 - 763.

 

 

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Lab News

Recent student presentations

Evan Simon presented his research at the 2022 TXSER in Austin entitled "The Relationship Between Elevation and Response of Trees of the Edwards Plateau to Drought." He won the first prize for an Oral Presentation by an Undergraduate Student.

Highlighted publications

A long-awaited Special Feature in the Journal of Ecology has finally been completed. These are our lab's contributions:

Schwinning, S., DeFalco, L.A., Esque, T.C. 2021.What common-garden experiments can tell us about climate responses in plants. Journal of Ecology 110: 986-996 pdf

Custer, N.A., Schwinning, S., Lortie, C.J., Esque, T.C., DeFalco, L.A. 2021. Local climate adaptations in two ubiquitous Mojave Desert shrub species, Ambrosia dumosa and Larrea tridentata. Journal of Ecology 110: 1072-1089. pdf

Other lab news

The following students have received research awards in 2022:

Evan Simons, who conducted research towards an undergraduate honors thesis, was awarded an undergraduate research followship by the College of Science and Engineering. He also won the first prize for the 'Best Undergraduate Oral Presentation' at the TXSER conference (Society for Ecological Restoration, Texas Chapter).

Owen Moorhead won the Ann Miller Gonzalez Graduate Research Grant from the Native Plant Society of Texas (NPSOT) to conduct an experiment in prairie restoration in collaboration with the Native Prairies Association of Texas (NPAT).

Silas Jenkins won the Ann Miller Gonzalez Graduate Research Grant from the Native Plant Society of Texas (NPSOT) to investigate the importance of mycorrhizal fungi for the survival of oak seedlings under drought.

Contact information
Susan Schwinning
601 University Drive
312 Supple Science Bldg
Texas State University
San Marcos, TX 78666, USA
Email: schwinn@txstate.edu

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Comments on the contents of this site should be directed to Susan Schwinning