Scientists from Colorado State University have produced a first of- its-kind map of the height of the world’s forests by combining data from three NASA satellites. The map reveals that the forest canopy in the Northeast averages about 50 to 60 feet tall, very similar to forests in the Appalachians and in Central Europe. The data will be used to estimate regional carbon storage potential. “We think of our forests as being pretty tall, but on average, those in the Northeast are quite modest,” said Michael Lefsky, a remote-sensing specialist.
The reason, he noted, has mostly to do with age. Forests in much of the region are still regenerating after having been cut down for farming two centuries or more ago. Another reason for the somewhat low height of our forests has to do with the technology used to conduct the study. Because of the low spatial resolution of the data he examined, Lefsky had to average out very large areas and factor in areas that have little or no forest at all (farmland, for instance, and subdivisions).
The study found that the coniferous forests of the Pacific Northwest have the tallest canopies in the world, soaring above 130 feet on average, because Douglas fir and western fir trees typically grow much taller than the species common in eastern deciduous forests and elsewhere. Relatively undisturbed areas of tropical rain forests average 82 feet tall, while Canada’s boreal forests, dominated by spruce, fir, pine, and larch, have canopies that average about 60 feet.
The primary data Lefsky used to create his map came from a laser technology called lidar, which can capture vertical slices of forest canopy height by shooting pulses of light at the ground and observing how much longer it takes for light to bounce back from the Earth’s surface than from the top of the forest canopy. His map incorporated data from more than 250 million laser pulses collected during a seven-year period.
“Lidar is unparalleled for this type of measurement,” Lefsky said. “It would have taken weeks or more to collect the same amount of data in the field by counting and measuring tree trunks that lidar can capture in seconds.”
Measuring canopy height has implications for estimations of the amount of carbon tied up in Earth’s forests and how much would be released if those forests were disturbed. The forest height map is the first step toward the creation of a global map of all above-ground biomass.
“In the Northeast, where the forest is still regenerating, the map gives us a sense of how much carbon could be stored over time,” said Lefsky.