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Are slash mats worth the cost?

October 17, 2007

Slash mats can further reduce soil erosion created by the equipment used to clear forest fuels from stream environment zones, according to a demonstration by the U.S. Forest at Heavenly Creek on Thursday.

However, Forest Service Vegetation Management program manager Scott Parson's questioned, "Do you understand what the cost of that incremental benefit of operating over the slash mat is?"

Parsons said that to clear 22 acres, amounting to 1,900 tons of fuel from the Heavenly Creek stream zone cost a "little over $174,000." Ten percent of the stream zone did not have sufficient material to create a slash mat.

After being described as a "wick" that lit the Angora fire, clearing forest fuels from the stream environment zones in the wildland urban interface has been a public concern.

In the effort to reduce forest fuels in stream environment zones, the Forest Service has been using low impact equipment-harvesters and forwarders. This equipment "cuts to length" the tree to be removed, stripping the limbs from the tree and then cutting the trunk to a stump.

The innovation promoted by the Forest Service at the demonstration is that the harvester will now cut to length in a way in which the limbs and tops of trees fall in front of it. This creates an increased buffer between the soil and tires of the following harvester and forwarder.

Officials say this results in a mat of "slash" that further lowers the soil compaction of the already low-impact equipment. The soil and plant systems in stream environment zones act as filter for run-off and prevents soil erosion, both of which have a negative impact on the clarity of Lake Tahoe.

"Out of spending $7,000 an acre, roughly 50 percent of that cost was purely involved in dealing with that slash mat," Parsons said.

Parsons said that while this technology used to clear the forest isn't any cheaper than the alternative of having people on foot doing the clearing, it does have the definite advantage of low soil compaction.

"If done by hand crews, you would have had hundreds of foot paths all through this area," Parsons said. "Plus it would have taken a whole lot longer to do."

Hydrologist of EC Adaptive Management Sue Norman said there was a "very rigorous monitoring component" in which soil quality criteria and infiltration capacities were met. She noted that soil compaction was tested in areas with and without a slash mat at the site.

"The results show that you get more compaction without a slash mat, but even without the slash mat there is still a positive result," Norman said.

"In the final report I think we'll be able to show that there is virtually no hydrological response from the treatment of this area," she added.

At the end of the demonstration, Lahontan Water Resource Control Engineer Doug Cushman restated the question asked earlier by Forester Parsons.

"When operating without a slash mat, water infiltration is half of what it is when they operated with the slash mat. Is that difference worth the cost?"

Cushman's question was directed to what the Lahontan Water Quality Control Board thinks about the benefits and costs of using slash mats.

However, this question should be asked of Tahoe residents who live next to stream environment zones.

If there is still a "positive result" for water clarity in clearing stream environment zones without the use of a slash mat, why stress the benefit of this technology after the Angora fire — especially if it costs more?

What do you think?

 

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Written by Dan Sorensen · Filed Under Community 

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