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 climatic changes result in species-specific responses, creating shifts in forest composition. Climate extremes like drought lead to tree mortality and reduce carbon uptake in the mesic forests of eastern United States. In this study, we use tree-rings to investigate differential drought responses of two co-occurring species, sugar maple (Acer saccharum) and white oak (Quercus alba), and whether the observed differences are consistent with a water-use (isohydric/anisohydric) framework. We sampled 781 tree cores from 418 individual trees in 18 forests. Pearson’s correlations were employed to analyze the radial growth response with climate variables such as maximum temperature (Tmax), precipitation, standardized precipitation evapotranspiration index (SPEI) and vapor pressure deficit (VPD) during the common period of 1947 to 2006. Our results showed both species express significant positive response to June precipitation and SPEI and negative response to June Tmax and VPD (p<0.05). These results suggest SPEI plays a determinant role in growth control of both species. However, white oak shows a stronger soil moisture response than sugar maple which suggest that our finding is inconsistent with the isohydric/anisohydric framework. The inconsistent responses to soil moisture may be attributed to the wood anatomy, rooting depth, site characteristics, successional status and age-related growth. The failure of the water-use framework to explain species-specific drought responses in radial growth introduces uncertainty in our understanding of how drought impacts carbon sequestration. Understanding species-specific responses to drought is needed to improve future vegetation modelling in a changing climate that is projected to be hotter with more frequent droughts.
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.