A Method of Measuring Forest Canopy Response to the Paleocene Eocene Thermal Maximum (PETM) Greenhouse Event

Science Center, Bent Corridor

How will climate change affect vegetation over long timescales—thousands to hundreds of thousands of years? In order to understand this, we can look to similar events in the past. The Paletocene Eocene Thermal Maximum (PETM) occurred 56 million years ago and involved a major spike in temperature in a short amount of time (5-8 degrees centigrade in about 150,000 years) caused by a spike in atmospheric carbon dioxide. Increases in atmospheric carbon dioxide may possibly have had a fertilizing effect on some types of vegetation. To figure out the exact effects on vegetation and forest health, canopy density is a useful measure and can be quantified as Leaf Area Index (LAI, foliage area/area of ground). It can be predicted observing morphological changes in epidermal leaf tissues preserved in modern and fossilized leaf cuticles. To calibrate paleontological data with a modern calibration set, modern leaves extracted from known canopy densities from soil samples are collected from a variety of canopy types and densities from Argentina, Ecuador, New Zealand, and Costa Rica. The epidermal leaf cells are photographed under fluorescence microscopy and measured using the application Image J. The same process of photography and measurement is then done for cuticle samples pulled from plant fossils distributed across time in the stratigraphic section in Hanna Basin, WY. Using our statistical model of modern plant cell measurements, we reconstruct LAI for the environments represented by the fossil samples. With this information, we can determine whether the high CO2 and warming had a fertilizing effect on forest canopies.