Abrupt changes in climate can result in species-specific responses, creating shifts in forest composition. For example, extreme climate events like drought can lead to tree mortality or reduced carbon uptake. Of particular interest is how drought impacts the mesic forests of the eastern US, where there is potential of drought converting this biome from a carbon sink to a carbon source. In this study, we use tree-rings to ask: (1) How do two co-occurring species, sugar maple (Acer saccharum) and white oak (Quercus alba), differ in drought response?, (2) Are site-specific differences more important than species-specific traits in influencing the drought response of these two species?, and (3) Can the isohydric/anisohydric framework explain differences in growth-climate response of these two species? We sampled co-occurring sugar maple and white oak in 15 forests and, in total, 538 tree cores from 295 individual trees were synthesized. All the cores were processed with standard dendrochronological approach. The samples were detrended to remove biological growth trends and non-climatic signals to maintain the climate-related responses. Pearson’s correlations were employed to analyze the growth response with climate variables such as maximum temperature, minimum temperature, precipitation and Palmer Drought Severity Index (PDSI) during the common period.
Results/Conclusions
Our results show that both sugar maple (Acer saccharum) and white oak (Quercus alba) show significant positive response to June precipitation and June, July, August (JJA) PDSI and negative response to June maximum temperature (p<0.05), except for one site respectively for both sugar maple and white oak. These results suggest JJA soil moisture content plays a determinant role in controlling the growth of both species. However, white oak shows a consistently stronger response to soil moisture than sugar maple. Mann-Whitney U test demonstrates the slope values between individual white oak cores and JJA PDSI are significantly higher than that of sugar maple (U=5781, p<0.001), indicating white oak is more sensitive than sugar maple.
These results suggest the co-occurring sugar maple and white oak respond differently to soil moisture but the iso/anisohydric framework does not explain differences in climate-radial growth response. The inconsistent responses to JJA soil moisture may be attributed to the site characteristics, successional status, and age-related growth. Understanding species-specific responses to drought could enhance our knowledge on future vegetation modelling as well as the possible impacts on the ecosystem services provided by sugar maple and white oak.