Seeing the Forest for the Trees: The Physiological Responses of Temperate Trees in a Warmer World

A forest’s ability to sequester carbon dioxide depends on factors such as periodic disturbance regimes, land-use change, the composition and productivity of the vegetative community, and the location and age of forested stands. However, one of the driving forces that contributes to changes in forest carbon dynamics include climatic factors, such as changes in temperature and precipitation, as well as atmospheric CO₂ concentrations which can affect the physiology of plants in complex ways. Our theorized understanding of plant physiological response to changing environmental conditions have been based on latitudinal and altitudinal studies or greenhouse experiments that measure plant physiological traits on one or a handful of plant species – and as scientists work to reduce the large variability that exists behind climate projections and plant community predictions, the need to collect locational and species-specific data becomes increasingly evident. This dissertation aims to address this issue by examining the physiological responses to temperature for 23 different tree species that have historically different geographic range distributions categorized into three groups: northern, central, and southern. The ranges of all species overlap and coexist at Black Rock Forest (BRF), an eastern deciduous forest located in the Hudson Highlands of New York. Chapter 1 examines the physiology of 16 coniferous and broadleaved tree species to determine if geographic provenance has a significant effect on foliar respiration rates, response to elevated temperature, and the respiratory substrate used to fuel the respiratory process. Chapter 2 compares the photosynthetic capacities and temperature responses of 17 broadleaved tree species to determine which range group may be more tolerant of a warming climate. Appended to this dissertation is preliminary data of a growth chamber experiment, examining the plasticity of physiological traits expressed under elevated temperatures to assess whether northern red oak seedlings show potential to acclimate to projected climate conditions and regenerate with minimal physiological constraints. Collectively, the results of these studies find significant differences in photosynthetic capacities and photosynthetic and respiration responses to temperature among species and among range groups. Northern, central, and southern ranged trees show an acclimated response to carbon assimilation under current climate conditions. However, central ranged trees, which includes the northern red oak, a dominant tree species in this region of New York, may be at a physiological disadvantage, showing lower rates of photosynthetic capacities and a trending decline of carbon assimilation under elevated temperatures. Furthermore, preliminary data from a greenhouse experiment suggests that leaf morphology and physiology traits are not plastic for northern red oak seedlings, which further weakens its physiological competitiveness and regeneration potential under warming temperatures. The results presented in this study on the physiological traits and temperature responses not only allows for a more thorough understanding of the physiological tolerances of migrant and resident tree species in the New York region but provides new data that could be incorporated into carbon and species distribution models for better predictions on carbon sequestration of forests and geographic ranges of tree species