LiDAR Maps World’s Tallest Forests

A new study using laser pulses shot from satellites has found that the world's tallest forests are along the Pacific Northwest coast, Miami Herald reports. The temperate forests of Douglas fir, Western hemlock, redwoods and sequoias that stretch from northern California into British Columbia easily reach an average height of more than 131 feet. That's taller than the boreal forests of northern Canada and Eurasia, tropical rainforests and the broadleaf forests common in much of the United States and Europe. The only forests that come close are in Southeast Asia, along the southern rim of the Himalayas and in Indonesia, Malaysia and Laos.

Scientists suspect that the forests with the biggest trees store the most carbon, and the Northwest forests are probably among the largest carbon sinks in the world. However, they also say that while slower-growing older trees store more carbon, younger trees also absorb more carbon as they grow rapidly.

That sets up a debate about how forests should be managed, particularly whether older trees should be cut to make way for younger ones or whether they should be protected to store the carbon they contain.

Ongoing studies using the satellites and LiDAR may provide valuable information on how fast the forests are growing and how much carbon they store. "All of the remote sensing is providing us with the ability to monitor changes in the environment in a way you might not see on the ground," said Michael Lefsky, an assistant professor in the department of forest, rangeland and watershed stewardship at Colorado State University. "We are expecting under global warming that the productivity of the forests will change."

With the help of computers, Lefsky put together a global forest height map based on LiDAR data from 250 million laser pulses collected during a seven-year period. "It's like an echo," said Lefsky, whose findings were published in the journal Geophysical Research Letters. Overall, LIDAR offered direct measurements of only 2.4 percent of the Earth's forested surfaces. "This is really just a first draft and it will certainly be refined in the future," he said.

LIDAR measures the height of forest canopies by shooting laser pulses and measuring how much longer it takes for them to bounce back from the surface than from the top of the forest canopy. The pulses can penetrate through the canopy to the ground.