Dendrochronology

 

People have been aware that trees record information about their environment for quite a long time.  Natural philosophers such as Theophrastus and even Leonardo Di Vinci documented the annual bands produced by trees and determined/hypothesized that their width might be related to local weather conditions.  However, it was not until the early 20th century that the science of dendrochronology, the method of assigning precise annual dates (dating) to individual rings within a tree, was solidified as a formal scientific approach to study past events and environmental conditions.  The counting of rings has long been used to ‘age’ a tree, but this method can only be applied to living trees, and may be inaccurate due to odd growth patterns, double rings, or even missing rings around the stem.

Andrew Ellicott Douglass, an astronomer from the University of Arizona, devised a method to compare patterns of large and small rings among trees to assign precise calendar dates to each ring.  This technique of matching patterns of large and small rings is known as ‘crossdating’ and gives dendrochronology the ability to be an annually resolved record of environmental variation.



Douglass’s method allows for not only living trees to be used to study the environment, but by matching the unique growth patterns samples of dead wood from the forest floor or from buildings  can be effectively dated as well. This allows scientists to study specific events thousands of years into the past and to better understand how forests responded to climate and disturbance events such as drought, fire, human activities, and even volcano eruptions.

Dendrochronology was first showcased in dating the abandoned settlements in the American Southwest and has since been applied to study climate and ecology around the globe.  Trees are some of the oldest organisms on the planet and researchers have used tree rings to standardize carbon dating techniques, study ancient civilizations, and reconstruct climate conditions thousands of years into the past.

 
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“The trees composing the forest rejoice and lament with its successes and failures and carry year by year something of its story in their annual rings.”

-A.E. Douglass

 
 

Forest Ecology

 
 

Forest are complex ecosystems with many interactions and feedbacks that make it difficult to fully understand what controls dynamics such as growth, mortality, and regeneration.  I use a combination of ecology and dendrochronology techniques to understand how trees interact with one another and how they respond to weather and climate conditions. My work focuses on understanding how individual trees respond to the combination of climate and competition pressures and how their individual responses shape regional forest functioning.  To this end, I study the microscopic--anatomical features like cell size and structure--and macroscopic--species composition and canopy position--components of the forest to determine how these attributes affect a tree’s response to its environment at long and short time scales.

 
 

Pre-settlement History

 
 

Because of the intense settlement practices in the eastern US, few old, remnant forest stands remain.  However, often the oldest trees left on the landscape are not found in a remote forest, but rather are preserved in houses and barns.  Settlement-era structures composed from local timber sources can provide insights into forest conditions further back in time than most living trees.  

I non-destructively sample the wood from pre-settlement structures to simultaneously determine building dates for historical structures and understand forest conditions hundreds of years into the past, prior to intensive land cover conversion following European Settlement.  

Historical buildings are not only an invaluable resource for conducting science, but they also provide an unparalleled avenue to connect and share science with people.  People seem to seek a connection with history and tree-ring provide a great avenue for these connections.



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