The Cameron Peak Fire burned 208,000 acres, more than half of that in the Poudre watershed. Mr. Bowker and many others had spent the spring poring over maps, made by federal agencies from aerial photographs, showing the severity of the slash and burn across the area.

The destruction caused by forest fires is anything but uniform. If a fire is spreading rapidly, there may be little or no damage to the canopy, underbrush, and soil, and the area may be exposed to little risk of erosion.

At the other extreme, a hot-burning, slow-moving fire can burn anything – trees, undergrowth, even the organic layer in the ground, creating ash and releasing nutrients. Waxy compounds in the leaf litter evaporate and later settle on the ground, causing it to repel water instead of absorbing it. That will increase runoff and erosion.

In the Cameron Peak Fire, more than a third of the country suffered a medium to high fire severity. About 10,500 acres have been identified as high priority areas that are likely to suffer severe erosion, Bowker said.

“We looked at where the greatest impact will be in the watershed,” he told the volunteers, “and you’re standing on one of them today.”

In addition to staking the straw tubes, the so-called wattles, over a slope, the volunteers distributed mulch and seeds. “It’s not hard work, but a lot of work,” said Tim Cochran, whose wife Carol and her family have owned the ranch for generations.

Nearby, another crew of volunteers were working on a slope where Ms. Astvatsaturova and others had determined that the water was likely to drain into a gully and into a deeper torrent, which could worsen erosion. To contain this water, the team built a series of block weirs or dams every 10 feet or so in the gully.