Schwinning Lab

Plant Ecology

Yang Tse

Tree Mortality

Dead junipers
Areas of high juniper mortality in the Texas Hill Country as seen from the air

Pinyon mortality

In New Mexico, Arizona and Utah, pinyon pine trees have died off in large numbers since 2002

The Texas Drought of 2011 killed 6% of all trees, equivalent to 300 million trees statewide. This event was one of many tree-dieoff events that have been documented world-wide in the past decades. Trees can normally withstand drought, but when coinciding with extremely high temperatures, trees succumb. It is likely that global warming, by facilitating the occurrence of "hot drought", will make tree dieoff events more common in the future. To anticipate the regional and global impacts of this phenomenon, there is an urgent need to understand local risk factors that modify tree mortality based on species traits, community characteristics and physical site conditions.

Funded by the Land Change and Ecosystem Science research network at Texas State University and the Texas Ecolab Program, Graduate student Beth Crouchet has recently completed an extensive survey of trees in Central Texas. She identified some obvious and some not so obvious risk factors. As other studies have concluded, exposure to high temperature during drought was an important factor in locally increasing tree mortality.Somewhat paradoxically, sites with more soil cover had higher rates of mortality, probably because trees can build up to higher density between drought events on these more productive sites. High density of conspecifics was more closely correlated with tree death than overall tree density. This might have been the reason why a woody plant encroacher, Ashe juniper, suffered relatively high mortality rates. However, a high density of Ashe juniper did not increase the mortality risk of other species.

Our lab is beginning an new investigation of the ecosystem effects of tree mortality in the pinyon-juniper woodlands of New Mexico. In this NSF-funded collaboration with Marcy Litvak, Will Pockman, Robert Pangle (University of New Mexico) and Andrew Fox (NEON), we will examine the hydrological aftermath of tree mortality. Specifically, we will examine if the loss of a critical fraction of pinyon trees leads to further aridification of the ecosystem by inhibiting the redistribution of soil moisture in the root zone.




Lab News

Recent student presentations

Beth Crouchet and Nathan Custer presented on their research at the 2015 International Research Conference for Graduate Students at Texas State University, November 17 - 18, 2015:

Site factors influencing tree mortality during drought in Texas. Beth Crouchet, Susan Schwinning, Jennifer Jensen, Benjamin Schwartz.

Determining seed transfer zones for Mojave Desert shrubs. Nathan A. Custer, Susan Schwinning, Lesley A. DeFalco, and Todd C. Esque.

Highlighted publications

Scott Havill's paper on "Fire effects on invasive and native warm-season grass species in a North American grassland at a time of extreme drought" was highlighted in the October 2015 issue of Applied Vegetation Science (link).

Other lab news

The following students received awards and recognitions in the academic year 2015/16:

Beth Crouchet and Nate Custer received the Biology Department's "Certificate of Excellence"

Beth Crouchet was inducted into the National Honor Society of Phi Kappa Phi

Beth Crouchet received the the Graduate College Scholarship - Science & Engineering and the Lamar and Marilynn Johanson Graduate Endowment Award.

Wesley Collins received a Freeman Center Scholarship.

The lab was awarded two federal grants in 2015:

NSF proposal : DEB-1557176: "Collaborative Research: Hydrological tipping points and desertification of semi-arid woodlands".

The DOD Legacy Award HQ0034-16-2-0006: "Characterizing Mojave Desert shrub ecotypes to establish seed transfer zones for military range restoration".

Podcast interview

In September 2013, Susan was interviewed by Alan Knapp on a paper published in Functional Ecology. Listen to the podcast here.

Contact information
Susan Schwinning
601 University Drive
312 Supple Science Bldg
Texas State University
San Marcos, TX 78666, USA
Phone: (512) 245-3753
Fax: (512) 245-8713

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Texas State University

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