Extreme climate events such as drought can cause tree mortality and reduce carbon sequestration in the mesic forests of eastern United States. Different species in the diverse forests of the eastern US adopt specific strategies to cope with the extremes. Drought and other extreme events therefore can shift forest composition. Sugar maple (Acer saccharum) adopt a more isohydric strategy while, white oak (Quercus alba) adopt a more anisohydric strategy to dryness. Here, we test if the radial growth of these two co-occurring tree species differ in drought sensitivity and whether the observed difference is consistent to isohydricity water use framework that suggests sugar maple should be more sensitive to moisture than white oak. We sampled 781 tree cores from 418 individual trees in 18 forests where both sugar maple and white oak co-exist. We used standard dendrochronological field and processing methods. Pearson’s correlations and slope values were used to analyze the growth response with climate variables such as maximum temperature (Tmax), precipitation (PCP), standardized precipitation evapotranspiration index (SPEI) and vapor pressure deficit (VPD) during the common period between the tree cores and instrumental data. Using the climate data, we also predicted growth to determine drought and legacy effects.
Results/Conclusions
Sugar maple and white oak both generally respond significantly (p<0.05) to climate variables in June, positively with PCP and SPEI and negatively with Tmax and VPD, suggesting soil moisture in June was a dominant factor influencing the growth of both species. White oak generally had higher correlation coefficients to all climate variables than sugar maple during early growing season, although they were not significantly different. However, when examining the entire growing season, sugar maple was significantly more sensitive to drought. Our findings suggested the ability of isohydricity water use framework explaining species-specific differences in radial growth-climate responses is dependent on the portion of the growing season that is examined. For the month of June, both species are equally sensitive. However, when examining the entire growing season, we found support for the isohydricity explaining species-specific responses. The differential seasonality responses indicated future drought impacts will ascribe to both forest compositions and drought timing. In a forest that shifts from oak to maple dominated, future drought in the earlier portion of the growing season will remain important but drought in the later portion will increase in importance, indicating that future drought could have a large impact on carbon sequestration.