The big picture
Trees are important
Tree physiology is quantitatively important for life on earth. Trees and other plants dominate the global C cycle and strongly influence the climate via radiation and water cycle feedbacks.
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Climate is changingHumans have dramatically altered the earth. The video above illustrates the change in temperature, but we have also fragmented the landscape, altered nutrient availabilities, and changed the water cycle. How will trees respond?
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Future forests?
How will climate change affect the trees we care about and the forests they inhabit? How do trees and forests influence the progression of climate change? The interaction between trees and climate is central to our work.
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Elevated
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Elevated concentrations of atmospheric carbon dioxide tend to increase photosynthetic rates in trees. In a loblolly pine forest, this stimulated wood production for more than a decade, but this did not occur in the eucalypt woodland. Forests are currently providing an excellent natural resource in C sequestration, but it is not clear whether this will continue in the future.
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Drought and tree water relations
We know that drought reduces tree growth, but how much? How can we rigorously predict how drought will impact the photosynthetic rates of many different tree species?
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One of John Drake's recent papers compared several different formulations regarding how to model photosynthesis for four trees exposed to a series of experimental droughts using large rain-out shelters.
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Forest production across an age gradient
Forest production often declines with age
This is a classic issue in forest ecology. Odum (1969) assumed this was caused by increasing respiration costs associated with the accrual of woody biomass.
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North Carolina chronosequence
John established a chronosequence of forest stands dominated by loblolly pine (Pinus taeda) trees of varying age in the Piedmont region of North Carolina. He found that production decline with age, even with succession towards a shade-tolerant hardwood community.
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Hydraulic limitation of photosynthesis
Using measurements of leaf-level photosynthesis, stem sap flow, C isotopes, and a model, John showed that declining productivity in aging loblolly pines was related to increasing hydraulic limitation of photosynthesis as old pines grew tall.
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The hidden half: roots
Roots and soils are an important and often understudied component of trees and forests. John built custom gas exchange chambers for automated measurements of root respiration (above; published here). John has also studied soil nutrient cycling in temperate hardwood forests (published here), and how root exudation modifies soil nitrogen availability (published here).