Drought associated with climate change is predicted to increase in frequency and intensity in many regions. Tree species may not be able to meet the rapid pace of climate change, altering forest health, composition, and distribution. We investigate effects of drought on forests, and how drought interacts with management practices designed for a changing climate at the Adaptive Silviculture for Climate Change (ASCC) experiment. Specifically, we combine a drought experiment with adaptive forest management treatments to simulate future climate change scenarios in north-central Minnesota’s mixed pine forests. Rainout shelters, structures that block rain over plots of tree seedlings, simulate variation in moisture availability, and timing and frequency of drought within and across growing seasons. We have measured growth of multiple tree species, combined with plant physiology to test hypotheses that 1) the timing of drought within a season impacts its severity on seedling responses, 2) persistent effects of drought (i.e. legacies) impact responses across seasons and, 3) management treatments interact with drought responses by reducing stressful conditions, and that active management may be more successful at reducing drought stress.
Results/Conclusions:
Results from first year seedling growth in un-droughted (ambient) conditions showed lower growth at Control (no-action, passive management) ASCC treatments compared to Transition (heavily thinned, active management) ASCC treatments. In the second year, there was less impact of ASCC treatments on seedling heights, but diameter growth remained lower at the Controls. Drought treatments, initiated in the second year, caused greater growth reductions at Controls. For red pine, we observed low survival and lower growth at Controls compared to Transitions, likely due to disease and planting under dense canopy. Overall, there is evidence for an effect of ASCC management treatment on seedling photosynthesis (Anet), with lower values at Controls. We also observed lower photosynthesis in droughted treatments, with a trend of greater negative impact of drought in unthinned Control treatments compared to actively managed Transition treatments. These trends, along with measures like plant water potential, may help explain greater effects of drought on seedling diameter growth at Controls, compared to the Transitions and may be amplified in drier years. Our results and ongoing study help promote the health of future forests in the Great Lakes region, and provide insight for similar forest ecosystems systems elsewhere.