Somewhere deep in an unmapped ravine or inaccessible creek bottom in Northern California hides a secret. If it exists - and it might not - it would be as old as the Roman Colosseum, yet it has never attracted much notice.
It is the tallest tree in the world, a Sequoia sempervirens - a California coast redwood. And if it remains undiscovered to this day, that may soon change.
Scientists with Save-the-Redwoods League are using advanced new tools to literally scan the redwood forests of Northern California, hoping to create an ultra-detailed map of the forest floor.
The goal isn't to find the tallest tree of the forest. Rather, the technology aids in forest management, identifying the most at-risk spots in the forest - a problematic former logging road, for instance, or a tract in desperate need of thinning - and allowing Save-the-Redwoods and others to prioritize restoration efforts.
Mapping the canopy
Yet the airborne technology carries a bonus feature. As it scans the ground, it also simultaneously maps the forest canopy, giving researchers an equally detailed map and a relatively instantaneous way to separate true titans from mere giants.
No tree in the world grows taller than the California coast redwood. Whether there is a redwood taller than the tallest on the books - the 379.1-foot Hyperion, discovered and named just last year in Redwood National Park - is a matter of some debate. Most tall tree experts think not; some 95 percent of the likely habitat has already been explored.
But redwoods are tough to map, and the terrain is unforgiving. Scientists believe redwoods can grow to beyond 400 feet, and anecdotal evidence from loggers suggests some old-growth trees approached that height. Until now, however, the only way to find such leviathans was strictly old school: Hike into remote gulches and either climb the tree with a tape measure or try and take a reading from the ground.
This new technology - an array of lasers strapped to the belly of a plane flying slow and low over the forest - has the potential to peel back the secrets of the forest.
"As we look around, we realize we know a little bit about how these forests work, but there's a lot we don't know," said Ruskin Hartley, Save-the-Redwoods' executive director. "Everything we do has to be done with a dose of humility.
The laser-based technology, called LiDAR, for Light Detection and Ranging, is sort of a sonar of the sky. It sends thousands of pulses of light per second from a plane down through the forest canopy to the ground.
As pulses hit objects - tree tops, branches, rocks, streams - they bounce back. And as a plane flies slowly over the forest, millions of returning pulses are recorded and coded as to whether they're from the ground, the canopy, or some place in between.
Global positioning units on the plane and on the ground triangulate the location, providing accuracy to within 18 inches, said Dan Porter, Save-the-Redwood's director of science and planning.
The best maps currently, from the U.S. Geological Survey, are accurate to within 33 feet.
"At the moment . . . hikers can take a USGS map and go walk down the hill, and you could go by a giant landslide that's 25-feet tall and it's not on your map," Porter said. "Or you could walk by a little stream that's full of salamanders, and it's not on your map."
Those details are important.
The organization is using LiDAR initially to prioritize restoration efforts in a 25,000-acre parcel of Redwood National and State Park known as the Mill Creek addition. The parcel has 300 miles of dirt logging roads, each of which will eventually fail and dump its sediment into a creek. It has second-growth trees so densely packed that 1,000 or more grow in a single acre.
An old-growth redwood forest typically numbers between 30 and 50 trees an acre. Those second-growth trees will eventually get there, but right now they're in an all-out race, pruning their crowns in a bid to pop above the canopy, shade the others and win the day.
LiDAR will help pinpoint where that is happening.
"It gives you an objective way to look at a large landscape," Porter said. "We certainly don't have the money to restore 25,000 acres, nor should we if Mother Nature is going to take care of it on its own.
"What we're trying to do at Mill Creek is recover the natural characteristic and even the natural processes."
A hidden world
What's amazing about the redwoods, author Richard Preston noted in his recent book, "Wild Trees," is how much remains unknown, particularly about the biggest trees.
The forest was never fully "described" - akin to John James Audubon's description of North America's birds in the early 1800s or Charles Darwin's characterization of the Galapagos in the 1830s - until Humboldt State University Professor Steve Sillett and colleagues started publishing their systematic map the redwood canopy in 1999.
Scientists have since discovered a vast and rich ecosystem aloft in the gnarled, complex old growth crowns: soil, ferns, bushes and trees, lichens and amphibians. In complexity and animal species, an old-growth redwood forest rivals and possibly exceeds an old-growth Amazon rain forest.
Or did.
Ninety-five percent of the old-growth trees have been felled. Young redwoods have far simpler tops, and the trees growing now - replacements for what was harvested from Big Sur to southern Oregon in the span of a century - won't grow canopies capable of sustaining that diversity until 2500 to 2800, scientists suspect.
But some spots may be developing that necessary complexity, while others may be stagnating. LiDAR's ability to penetrate the canopy can point scientists in the right direction.
"You can do that by going into the forest, but LiDAR will tell you much more quickly," said Malcolm North, a research scientist with the U.S. Forest Service who also serves as an associate professor at University of California-Davis.
"For people like me who like to get away from the computer, that's just a bad situation. But LiDAR definitely has that potential."
Save-the-Redwoods hopes to use the tool to create an "objective" assessment of the forest's needs. The group has already removed 14 miles of logging roads and restored 1,080 acres in the Mill Creek parcel since 2003; it hopes to remove 20 more miles and restore 600 acres this summer.
The project marks an evolution in the organization's mission. The league was founded in 1918 to put the best of the remaining redwood groves into public ownership, and that remains a priority.
Save-the-Redwoods has purchased six of every 10 acres of ancient redwood forest protected today in public parks. But even in the '20s the league's founders wondered if these forests rejuvenated. With with most of the remnant old-growth protected, the league's attention is shifting to the second-growth stands, said Hartley, the group's executive director.
"We're not under the belief that we can restore the ancient forest," Hartley said. "But we do believe we can help reweave the fabric of the forest and facilitate growing the old forest of the future."
Man vs. machine
LiDAR isn't just used in the redwood forest. It is also used to map old growth stands in remote stretches of Idaho and Alaska and to track deforestation rates in tropical forests, among others.
In the tropics, a cut can be reforested within 10 years and, in satellite or aerial photographs, be indistinguishable from virgin growth, North said. LiDAR blows that cover, exposing a reforested tract as small trees without the structure or complexity of an old-growth canopy.
"It's been very effective at being able to get a handle on deforestation rates in Brazil and the Amazon basin," North said.
But can it find an undiscovered behemoth - a tree that tops 380 feet?
Few know the redwood forest better than Chris Atkins, who, with fellow naturalist Michael Taylor and Humboldt State's Sillett, has bushwhacked through nearly 95 percent of the surviving old growth stands.
Only four known trees in the world top 370 feet, and Atkins and Taylor have found them all. All are giant redwoods; the three tallest were found during a single eight-week stint last summer while the pair was scrambling about in a remote tributary to Redwood Creek, in Redwood National and State Park.
Atkins doubts a taller one exists, though he acknowledges he said the same thing three years ago, after discovering what was then the record-holder, the 370-foot Stratosphere Giant.
"It's nice," he said, "that there are some things we don't know - that there is the promise of future discoveries out there."San Jose Mercury News
