Mesophication from oak to maple: a tree-ring perspective in the forests of eastern United States

Mr Tsun Fung Au1, Dr. Justin Maxwell1, Dr. Neil Pederson2, Dr. Grant Harley3, Dr. Matthew Therrell4, Mr. Scott Warner5, Dr. Frank Telewski5, Dr. Scott Robeson1, Dr. Richard Phillips1, Dr. Kimberly Novick1

1Indiana University, Bloomington, United States, 2Harvard Forest, Harvard University, Petersham, United States, 3University of Idaho, Moscow, United States, 4University of Alabama, Tuscaloosa, United States, 5Michigan State University, East Lansing, United States

Abrupt and continuous climatic changes can result in species-specific responses, potentially creating shifts in forest composition and species distribution. Climate extremes like drought can impact forest productivity, resulting in tree mortality in mesic environments. In this study, we investigated differential drought responses by examining the radial growth of two wide-ranging and co-occurring species, sugar maple (Acer saccharum) and white oak (Quercus alba), in the temperate deciduous forests of eastern United States. We sampled 781 tree cores from 418 individual trees at 18 locations to test if species-specific climatic sensitivity differences were present in radial growth and whether the differences are consistent with the isohydricity water-use framework. We found that radial growth of both species significantly responded to climate variables, but white oak generally had stronger climate-growth relationship than did sugar maple during June. However, sugar maple was significantly more sensitive to drought when examined over the late and entire growing season. These results suggest that the ability of the isohydricity water-use framework to explain species-specific radial growth responses is highly dependent on the portion of the growing season examined. The differential seasonal responses between the two species indicate the mesophication of species in the eastern US could increase the impact of drought. In a forest that shifts from oak- to maple-dominant, early growing season drought will remain critical but drought in the later season will increase in importance on affecting species survival and distribution. Projected temperature increases in combination with forest mesophication indicate that future drought could have substantial impacts on tree mortality and distribution in eastern US forests.


Tsun Fung (Tom) Au is now a PhD student at Department of Geography, Indiana University, studying species-specific tree growth responses to climate changes and the impacts on future forest dynamics and distribution.

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