Site Factors Involved in Texas Tree Mortality During Drought – Beth Crouchet

On Wednesday night, CAMN member and recent Master’s degree recipient, Beth Crouchet, presented her research at our monthly public meeting. She outlined her methods of collecting field data over two years from 64 sites spread across Texas, focusing eventually on mostly Central Texas and o 9 tree species, including live oak (Quercus fusiformis), yaupon holly (Ilex vomitoria), ashe juniper (Juniperus ashei), Texas persimmon (Diospyros texana), and others. Beth was interested in discovering some answers to what specific site factors affected trees when they encountered the intense Texas drought in 2011. Some of those site conditions include soil type, soil depth, slope, aspect, exposure, and site-specific weather data.

In her research, Beth defined some basics, such as what actually constitutes a dead tree – how much of the crown must be dead?  Does a re-sprouted tree count? And how recently can it have died? With extensive data mining derived from her data set, Beth was able to demonstrate that certain species, for example ashe juniper, showed more likelihood to die back during extended hot drought – periods not only of little precipitation, but ongoing high temperatures. While this was an expected outcome, her data revealed a few interesting conclusions. Some species, including yaupon holly, showed a striking ability to thrive over extended hot drought conditions, while others were not as noticeably impacted.

In some ways, Beth’s talk and her research opened many questions, inviting audience members to wonder what trees might fare better in intentional landscape conditions, or what ongoing drought might mean for future forest species diversity.

While the work outlined in the talk covered a somewhat specific look into tree mortality – Beth purposefully stayed away from aggravating factors linked to insects, fire, lightning, etc. – a parallel view of her presentation might reveal the process behind field research and deriving meaning. Not just the glimpse of what kills trees, but the work it takes to turn a big question into answers. One gets a sense of the painstaking work… the parameters to be defined, second-guessed, re-defined, the amount of time spent in hiking boots on Texas hillsides and plains, the statistical analyses done late at night while the kids sleep, the singular devotion to following something to a conclusion at the expense of many of life’s other demands and desires.

Coincidentally, it turns out, Beth’s not the only one looking at similar factors. The day after the meeting, NPR posted a story about the canopy-swinging biologists – and their drones – researching how certain giant sequoias are surviving California’s hot drought. Read more about it here.