The team drew up an "idealized tree" to represent an average model of all tree species in the United States and developed equations to represent the relationships between fluid flow rate, tree size, and meteorological factors such as average temperature, rainfall, humidity and sunlight.
Putting their model to work, the group predicted the height of the tallest trees across the country, using local meteorological data. Kempes compared the team's results with actual measurements from the United States Forest Service. The predictions from the model matched up well with the Forest Service data, except for two geographic regions: the arid Southwest and parts of New England.
In the Southwest, the team found that trees actually grew taller than the model predicted, possibly due to evolutionary adaptation. "Deserts are where you find many specialized trait adaptations," Kempes says. "This is where you have weird traits that can deal with harsh environments."
In New England, trees were a bit shorter than predicted, primarily because the model did not factor in the area's timber and logging history. New-growth forests simply haven't had time to recover, but if left undisturbed, Kempes says they will eventually catch up with the model's predictions.
The group used the same model to predict what would happen to tree height in the event of global temperature changes, and found that with an increase of 2 degrees Celsius across the country, the average height of the tallest trees would shrink by 11 percent. Conversely, a dip of 2 degrees Celsius would spur trees to sprout up by 13 percent.
Going forward, Kempes and his colleagues plan to use the model to "
|Contact: Caroline McCall|
Massachusetts Institute of Technology