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

Tree mortality by drought or fire has become a persistant phenomenon over the past decades. It is highly likely that global warming, by facilitating the occurrence of extended drought conditions or "hot drought" conditions has amplified tree mortality world-wide and will continue to do so. The sudden loss of live tree cover alters ecosystem function and the provisioning of ecosystem services in the short term, but little is known about the long-term consequences, for example how these ecosystems will recover. There is an urgent need to understand not just local risk factors, but also how the associated perturbation in carbon and water fluxes sets the stage for future vegetation change.

Graduate student Beth Crouchet has recently completed an extensive survey of tree mortality in Central Texas. Conducting a survey study relating mortality rates to local site and climate factors, she identified potential risk factors. As other studies have concluded, exposure to high temperature during drought is an important amplifier of local tree mortality. Somewhat paradoxically, sites with more soil cover had higher rates of mortality, probably because trees had build up to higher density on such sites. High density of conspecifics was more closely correlated with tree mortality than overall tree density. Thus, Ashe juniper, which is a woody plant encroacher in Central Texas, suffered relatively high mortality rates, but high densities of Ashe juniper did not increase the mortality of other species.

The lab is also engaged in research to examine ecosystem consequences of tree mortality in the pinyon-juniper woodlands of neighboring New Mexico. In this NSF-funded collaborative effort with Marcy Litvak and Will Pockman at the University of New Mexico, a plot level experiment is underway involving the selective girdling of either juniper or pinyon pine trees. We are testing the hypothesis that effects of dying pine and juniper trees on are different, the former leading to desertification by disrupting hydraulic lift, the latter improving plant water availability and facilitating recovery. Results from this study are important for improving understanding of vegetation-atmosphere feedbacks in Earth System Models.




Lab News

Recent student presentations

Nathan Custer presented on his research at the Ecological Society of America Meeting in Portland. The title of his presentation was "Effect of transplant size on early survivorship". The paper was presented in a session on "Multiple Common Garden Experiments for Meeting Restoration Challenges: Difficulties and Potential Pitfalls" organized by Susanne Schwinning and Lesley DeFalco.

Highlighted publications

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

Dammeyer, H.C., Schwinning, S., Schwartz, B., Moore, G. 2016. Effects of juniper removal and rainfall variation on tree transpiration in a semi-arid karst: Evidence of complex water storage dynamics. Hydrological Processes 30: 4568-4581. pdf

Other lab news

The lab welcomes two new graduate students:

Kayla Sustaita will examine the effects of adaptive rotational grazing on soil characteristics.

Logan Maxwell will investigate best restoration practices for abandoned oil and gas exploration fields in Utah.

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".

In the media

In August 2016, Susan was interviewed by Salwa Khan for the Wimberley Valley Radio show "Mothering Earth" Listen to the podcast here.

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