PS 7-68
Inter-annual differences in the water use of mature sugar maple in response to experimental soil warming and irrigation
Mean annual temperature is expected to increase 3-5º C in the Upper Midwestern USA by 2100. Sugar maple (Acer saccharum), an economically important species for both timber and syrup production, is not expected to do well under current climate projections. Sugar maple crown dieback, likely related to decreased water availability, is increasing in the region and could be exacerbated further by warming. The objective of our study was to investigate the effects of experimental infrared soil warming and irrigation on the water use of sugar maple. We installed heat dissipation sap flow sensors in 33 trees over three growing seasons in a mature sugar maple-dominated forest in Michigan’s Upper Peninsula. Trees were instrumented in a full factorial design including eight 100 m2 plots with two replicates each of four treatments: 1) heat-only (3-4 °C above ambient soil temperature), 2) water-only (20% above ambient precipitation), 3) heat+water, and 4) control. We hypothesized that tree transpiration would increase in the water-only treatment and decrease in the heat-only treatment, yet we expected no change in the heat+water treatment due to supplemental water counteracting the negative effects of warming-induced soil evaporation.
Results/Conclusions
Results from Year 1, which was a normal year with respect to growing season precipitation, confirmed our initial expectations, as transpiration increased with irrigation, decreased with warming, but did not change relative to the control with the combination heat+water treatment. In Year 2, however, which was a drier than average year, both the heat and heat+water treatments showed decreased rates of transpiration, while the water-only treatment was no different than the control. Year 3 was a wetter than average year, yet we found decreases in all treatments compared to the control, which was likely more due to an artifact of cumulative wound response in the trees with older probes than it was due to an actual decrease in sap flux rates. Overall, this study indicated that when water was not limiting, increased temperature alone had minimal effects on the water uptake rates of sugar maple, but that warming-induced drought effects could potentially exacerbate sugar maple sensitivity to climate change and potentially increase the prevalence of crown dieback.