RAPID: Collaborative Research: What are the Mechanisms of Tree Recovery after an Extreme Episodic Drought?

Regents Of The University Of Idaho, Moscow ID

Investigators

Abstract

The 2011 drought in Texas, Oklahoma, and eastern New Mexico was the most severe one-year drought in the region since meteorological record-keeping began in 1895 and potentially the worst single-year drought in over 1200 years. This drought continued through 2014 and killed a half billion trees in Texas between 2011 and 2014. Research on trees during this drought documented patterns of mortality, photosynthesis, and water use for individuals spread across several research sites. This project examines how these same landscapes and trees respond to alleviation of drought. Central Texas has gone from an extreme drought in August of 2011 to essentially no drought in July 2015, due to one of the wettest spring and early summer periods on record. This provides a unique "natural experiment" in which to test hypotheses about those plant traits associated with resistance to drought and recovery from drought. A primary hypothesis to be tested is that species that were able to maintain greater photosynthesis during the drought will recover more quickly (i.e. will maintain greater photosynthesis and will exhibit greater growth) than those species that were unable to maintain photosynthesis. Because more extreme and episodic climate patterns are predicted for the near future, this research will contribute to the understanding of how vegetation will respond to extreme variation in water availability. This information will be particularly useful to land managers to ensure the presence of vegetation and the maintenance of the ecosystem services that vegetation provides. The project also involves training of undergraduate students and postdoctoral associates in plant stress research. The frequency and intensity of episodic droughts are predicted to increase in the future, and these patterns have already been observed over the last 15 years. However, little information exists about what physiological changes occur in naturally-growing trees that survive a severe drought. Central Texas experienced the worst single-year drought in its recorded history in 2011. That drought continued through 2014 and killed an estimated half billion trees. In 2015, Central Texas experienced late spring and early summer rainfall that exceeded long-term averages by 10 times. Climate predictions for the area for the next three months are for below average temperatures and above average rainfall. This unusual combination of climatic events provides a unique situation in which to study vegetation responses to rapid alleviation of drought. A major advantage this project exploits is the previous characterization by the investigators of physiological and hydraulic conductance responses of trees to the severe 2011-2014 drought. These same individuals and sites will be measured for physiological parameters (gas exchange, hydraulic parameters), anatomy, and growth to allow the comparison of measurements taken during and after the drought. The measurements will be used to parameterize a process-based model to predict the carbon and water status of these trees under different moisture availability scenarios. The project has significant broader impacts in land management and conservation of forests under extreme variation in water availability. Undergraduate students will be involved directly in the research, along with postdoctoral associates. The results will be used for public outreach at two of the participating institutions relating plant response to changing environments.