Scientists are getting loftier look at forests
‘Rain of laser pulses’ sent from planes paint 3-D map
BLUE RIVER, Ore. – Scaling a 280-foot Douglas fir in the H.J. Andrews Experimental Forest, biologist Matthew Betts can spot evidence of the animals that depend on the old-growth tree, from the arthropods that burrow into the bark to the woodpeckers that dig them out.
He and the tree-climbers on the site last week use a system of ropes, harnesses, carabiners and other equipment to inchworm their way up to the canopy, where earlier the climbers had dropped a tape measure to size up the tree.
But measuring the exact height of a tree, and counting the layers and extent of the branches that provide habitat, is labor intensive.
“It just takes an incredible amount of time,” said Betts, an assistant professor of landscape ecology at Oregon State University. It could take 15 minutes to measure one tree, he said.
But using a growing technology that involves shooting lasers from airplanes to accurately and quickly create three-dimensional maps of the ground and vegetation below, Betts and other researchers are discovering more about the forest ecosystems in Oregon.
“It allows us to see the forest in new ways,” said Thomas Spies, a research forest ecologist with the U.S. Forest Service’s Pacific Northwest Research Station.
While in oceanography it’s hard for researchers to figure out what’s on the deep ocean floor, he said, in forestry it’s the opposite – scientists need to know more about the canopy. And the new technology, called “light detecting and ranging,” or LIDAR, will help them get a more detailed picture of life 250 feet up above the forest floor, without the need to scale individual trees.
LIDAR involves flying over areas in aircraft with specialized equipment that can shoot thousands of pulses to cover the forest.
“It creates basically a rain of laser pulses,” Spies said.
The pulses travel until they hit something – whether it’s the top of a tree, lower branches, shrubs below or the bare ground – and then they bounce back up to the plane. By calculating how far the pulses traveled, the equipment can determine the shapes and sizes of the area below.
“It’s like draping a very light cloth across a canopy,” Spies said. The cloth would catch on the peaks of the canopy, but fall down into the gaps between branches and vegetation as well.
Over large areas like the 15,000-acre Andrews Experimental Forest, LIDAR costs about $2 per acre.
And with those maps in hand, scientists can start asking questions that would have been difficult to investigate previously.
Betts, for example, has worked on identifying bird habitat based on the structure of the forest layers. Once researchers know which types of habitat birds favor, they can use LIDAR to see how much of that habitat exists within a forest and make estimates of the bird population.
And they can also track how much habitat is lost for specific species over time, Betts said.
LIDAR could also be useful in helping to take detailed measurements of trees in spotted owl habitat, he said, and then making predictions about where other owls could be either currently or in the future.
LIDAR could also be used to estimate how much carbon the trees in a forest contain, Spies said, as people consider the value of forests in reducing greenhouse gases.
“There’s a lot of interest in understanding when, where and how much carbon is stored in forests of different kinds,” he said.
Or forestry researchers can use the technology to spot where trees are growing the tallest, and then identify what kinds of growing conditions can lead to the biggest trees, Spies said.
LIDAR could show forest specialists where there are areas that are prone to landslides, or where roads need to be repaired, said Helen Maffei, forest health specialist with the Deschutes National Forest.
Knowing where the tallest of the tall trees are could help the forest determine where to locate timber projects, or where to prioritize firefighting efforts, she said. Others could use LIDAR images to see how much vegetation is on the ground – and whether it makes certain areas more prone to catastrophic fires.