Home Science & Technology See a laser scan of Yosemite forests after forest fires

See a laser scan of Yosemite forests after forest fires


The forest can take many forms: prickly with oak undergrowth, dull and mossy, or sunlit and full of soft grass. These structures affect the animals that live there, the amount of carbon that the ecosystem can store, and how the forest fire will move through the landscape. But if the casual tourist doesn’t know what to look for, it can be hard to spot these landscape-scale specimens.

A set of excellent LIDAR scans of Yosemite National Park in California, published by forest ecologists from the University of Washington and a company engaged in remote imaging NV5 Geospatial y EOS this monthoffers a glimpse into the subtle differences in forests and the enormous effects of forest fires on an area of ​​100 square miles.

[Related: The American West is primed for a summer of fire]

The project started as part of the US Geological Survey 3D Altitude Program, which creates topographic maps of landscapes across the country. NV5 collects altitude data for these maps by flying back and forth over Yosemite and throwing a laser at the terrain below. By measuring the time it takes for a laser to bounce to a plane, a technology called LIDAR can map the surface into fine detail, even detecting individual trees.

To make a topographic map, NV5 just needs to find out where the laser got to the ground under the trees. But LIDAR also captures accurate details on trees and undergrowth above ground. «[Light] continues to descend through the canopy – part is reflected, and part continues to go until it falls to the ground, “- says Andrew Brenner, program director of NV5.

Leading Yosemite scans can show both ground height and trees and shrubs (colored to make it easier to distinguish individuals). Provided by NV5 Geospatial

Using Yosemite scans taken between 2010 and 2019, forest ecologists from the University of Washington were able to map how fires are changing the fabric of the landscape.

Before the mass adoption of firefighting by U.S. Forest Service in the early 1900s, most North American landscapes burned regularly, including most of the Yosemites. And environmentalists now know that burning forests are very different from non-burning ones. In the mixed ecosystem of pine and fir, which covers most of the Yosemites, repeated fires thinned small trees, creating patchwork from clumps of mature forest and open meadows.

These “natural fire breaks” in the patchwork forest mean fires will usually be less intense: They will rush through grass and bushes instead of “burning” entire tree plantations. This reduces the risk of fires to humans, but can also benefit local ecosystems by creating habitats for sun-loving wildflowers, edible plants and birds.

Open design was “the key to making forests thrive in frequent fires,” the authors say write it down EOS. “However, firefighting for decades has allowed trees to fill openings, creating dense stands prone to intense fires.”

Intense fires, burning dense forests and drought-stricken trees, can cause an environmental cascade. They can burn the soil and burn seedlings, making forests difficult to recover from, as well as from softer burns. Across the West, forest landscapes are turning into open meadows as a result of fires.

However, for the past 50 years, Yosemite forest managers have tried to restore regular fires, both by setting up prescribed burns and by leaving room for lightning fires. But it takes time to undo decades of firefighting, all the more so as climate change complicates the search for a healthy, moderate burning zone in Goldilocks.

Current map showing the history of Yosemite fires by decade
In the West, moderate fire has been restored only for a fraction of its historical range. National Parks Service

In areas of the national park where fires were regular, researchers found that forests had opened up – and they could have survived better Rim Fire 2013on which hundreds of thousands of hectares were burned. But surprisingly, they saw that even a single low- and medium-intensity fire could leave a forest similar to a forest with conventional burns.

This means that even if the climate warms and the western forests dry up, one timely prescribed fire can significantly make the landscape more resilient.

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