PS 6-60 - Diversity of neighborhood hydraulic regulation mediates growth response during drought in temperate forests

Monday, August 12, 2019
Exhibit Hall, Kentucky International Convention Center
V. R. Kirk Acharya and Inés Ibáñez, School for Environment and Sustainability, University of Michigan, Ann Arbor, MI
Background/Question/Methods

Community composition and diversity have been shown to affect the growth rates of different tree species to varying degrees during drought events. Tree growth rates can be significantly affected by the density and richness of trees in the immediate vicinity, however the effects of neighbor identity are not widely understood for temperate forests. One mechanism that may explain growth rate as a function of neighbor identity is a difference in response to hydraulic stress. Trees are often classified along a spectrum of stomatal regulation behavior that ranges from completely shutting their stomata in response to drought in order to maintain interior water potentials (isohydric) to those that will leave their stomata open thereby sacrificing interior water potential for maintaining photosynthetic activity (anisohydric). Anisohydric trees surrounded by isohydric neighbors may therefore have higher access to water during drought periods as the neighbors shut down their water uptake, whereas isohydric trees surrounded by anisohydric neighbors may experience heightened drought stress. Such interactions have the potential to alter ecosystem properties such as resilience to drought. Here, we present results from a study where we measured yearly basal area increment for 44 Quercus individuals in southeastern Michigan, with tree-rings dating back to 2000, with the assumption of neighborhood preservation. We modeled growth as a function of neighborhood composition(species diversity and isohydry)in response to drought using historic drought records.

Results/Conclusions

Our results show a significant difference between growth when in the presence of isohydric versus anisohydric neighbors. Parameters in our model indicated that density of neighborhoods and severity of summer drought were strong predictors of yearly growth. Identity of neighbors showed significant effects on growth of target trees. We found that stand location and random effects did not play a major biological role in predicting yearly growth.These results suggest that species interactions will play a major role in the capacity for forests to respond to drought.