Luna Ardila Holzinger

This paper assesses how leaf-level physiology, growth, and competition for nutrients between species of mature trees respond to frost-induced defoliation. Spring frost-induced defoliation is when trees lose their leaves due to frost during April and May. Understanding trees' ability to recover from frost-induced defoliation is essential to accurately predict the effects of extreme climate events on ecosystem processes. The researchers in this paper specifically analyzed data from a spring frost event that caused substantial defoliation damage to trees across the Hudson Highlands Ecoregion in southeastern New York, USA in May of 2020. From this analysis, they addressed this question: How might leaf-level physiological parameters such as photosynthesis and stomatal conductance differ between leaves that developed prior to the defoliation year and those that developed following the defoliation year? During 2020 and 2021, red oak and red maple canopy samples were collected during the early (May 29–June 7), middle (June 16–July 7),  late (August 6–26), and end (September 11–20) of the growing season. The LiCor 6800 portable photosynthesis system was used with the Multiphase Fluorometer chamber to measure leaf-level photosynthetic capacity and stomatal conductance on 2–3 leaves per tree on each sampling date. It was found that the red oak leaves that developed following the defoliation year had photosynthetic capacities that were 3–4 times higher than red maple trees. Also, the photosynthetic capacity and stomatal conductance of red oak trees rapidly increased over the course of the growing season and were sometimes higher than the first-flush leaves during the reference year. From this, it is concluded that red oak trees exhibited a compensatory response in the physiology of second-flush leaves.