We examined the response of several northern Minnesota tree seedlings to simulated drought subject to enhanced heat stress with ambient and elevated CO2 under projected climate change in northern Minnesota forests. We present results here for three species: Bur Oak (Quercus macrocarpa), Quaking Aspen (Populus tremuloides), and Red Pine (Pinus resinosa). We tested hypotheses that that the combination of high temperature stress and drought conditions will be greater than the sum of the effects of the individual treatments and that increased water use efficiency under elevated CO2 will enhance plant tolerance to drought conditions.
Our preliminary results suggest that plant response to the combined effects of drought and short-term high temperature stress (T > 35o C) were greater than the individual effects when subjected to the seedlings alone. We also found that under elevated CO2 (800 ppm), seedlings were able to better tolerate drought conditions, but not increased at elevated temperatures above 42o C. We also made use of periodic digital photos to access the health of seedlings under a combination of drought treatments. Testing a number of different supervised and unsupervised classification methods, we were able to inexpensively quantify changes in overall seedling health. Finally, we discuss prospects for expanding our work to simulate drought conditions in the field at meaningful spatial and temporal scales and for the implications of our results for management of northern forests under future climate change.