LB 24-258 - MOVED TO BOARD #15 on WED - Forest responses to climate change are predicted by acclimation of xylem hydraulics to urban heat islands.

Background/Question/Methods:

Warmer temperatures exacerbate droughts in the 21st century by accelerating the evaporative drying from the land surface and vegetation. These ‘hotter’ drought conditions have resulted in increased rates of tree mortality globally. The ability of trees to adapt/acclimate their hydraulic systems to warmer, drier future conditions is a critical knowledge gap in accurately predicting the impacts of climate change on the globally important forest biome. In particular, how warming temperatures affect the spatial-temporal variation in key xylem hydraulic traits that confer tolerance to hotter drought is unknown. Responses of plant traits to climate change is difficult to study, yet, trait-based studies of urban forests provide an alternative ‘natural experiment’ because many of the predicted future conditions already occur in these environments. Therefore, we characterized key xylem hydraulic traits that confer vulnerability to hotter droughts in western US tree species, across an urban heat island gradient in the Portland Metro area. Trees were selected within discrete areas of the UHI, utilizing high resolution spatial and temporal urban heat models. Vulnerability curves of stem xylem were constructed and used to estimate the point of 50% loss in hydraulic function (P50), as well as other drought resistance traits.

Results/Conclusions:

Our results suggest that warmer temperatures induce complex, species-specific patterns in hydraulic traits, with some species exhibiting strong acclimation to UHIs compared to others. Furthermore, species identified as having low acclimation of xylem hydraulics were found to have increased rates of mortality in hot, urban sites. This work suggests that (1) the hydraulic traits of tree species may have divergent responses to warming temperatures and (2) urban environments are useful systems for developing predictions of how particular species will respond to climate change.