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NMSU Researchers Test Giant, Gentler Tree-Thinning Machine

RUIDOSO - A forest-thinning machine that grasps, cuts and de-limbs small-diameter trees in the blink of a lumberjack's eye is being studied by researchers from New Mexico State University.



Bob Rummer, left, of the U.S. Forest Service's Southern Research Station, and Doug Cram, a fire ecologist with New Mexico State University's Extension Animal Science and Natural Resources Department, evaluate the use of a harvester-forwarder to thin the forest near Ruidoso. (Courtesy Photo from NMSU)

The harvester-forwarder is a high-tech, powerful tree-handling workhorse, but the eight-wheeled behemoth is a gentle giant, rolling across the forest floor on extra-wide tires that leave a relatively minor footprint. And because the machine uses a long arm to harvest trees, it can park while it gathers trees within reach, rather than moving from tree-to-tree. Unlike traditional logging methods, logs are carried out in an attached bed, rather than dragged out, further lessening the damage to plants and soils.

"When you start dragging logs across the forest floor, you can create quite a bit of disturbance and rutting that is undesirable," said Terrell T. (Red) Baker, a Cooperative Extension Service riparian management specialist for NMSU's Range Improvement Task Force.

A 200-acre forest treatment at Eagle Creek, northwest of Ruidoso, was a good opportunity to study the differences in using the harvester-forwarder, so the U.S. Forest Service's Southern Research Station contacted NMSU researchers in the fall of 2004 to closely examine the machine's impact, focusing on soil disturbance, runoff and erosion.

The unnaturally dense forest at Eagle Creek is being thinned because of its closeness to populated areas and the danger it could pose should a wildfire ignite.

NMSU scientists visited the site before, during and after the thinning. They also conducted tests after the treatments to simulate rainfall and study runoff and erosion.

The machine's impact on the forest floor may even encourage plant growth, said Doug Cram, a fire ecologist with NMSU's Extension Animal Science and Natural Resources Department. In forests where the top branches of trees have blocked most sunshine from reaching the ground, the forest floor may become dormant, and over time, coated with forest litter - branches, twigs and needles - that further discourage growth. Even if the trees are thinned, growth of grasses and broad-leafed plants on the forest floor may not start.

"Some disturbance is necessary to get an herbaceous response," Cram said. Bringing in equipment like the harvester-forwarder can help break up the layer of litter and allow plant growth. Too much traffic, though, can cause more damage than good.

"It's sort of a balancing act," Cram said. "This is what the research will help determine."

Their findings will help Forest Service officials make decisions about use of the harvester-forwarder. Dennis Dwyer, forest timber staff officer for the Forest Service in the Lincoln National Forest, said the researchers' work is especially useful in deciding the best ways to restore forests.

"Restoration ecology is in its infancy," Dwyer said, "so the more information, the better. One exposed relationship leads to 10 more questions. We understand the basic tree density relationships and general ecological processes so this type of research will allow us to fine-tune (forest treatment) prescriptions and give decision-makers a better read on alternative treatment effects. New Mexico State has the capacity to do a more exhaustive and robust investigation into a myriad of critical effects." Little research has been done in mixed-conifer forests in the Southwest, for example, like parts of the Eagle Creek site, which also has some ponderosa pine stands, pinon and juniper.

"It's been tremendous to have help from a management perspective in dealing with these issues," Dwyer said.

Dwyer transferred to New Mexico from a national forest in eastern Oregon, where almost all forest treatments are done with mechanical harvesters. For loggers, the machines are more efficient and economical, and their lighter footprint is important to help preserve the area's pumice- and ash-covered soils, which are prone to displacement and compaction. These machines are safer, and operators see reduced occupational insurance rates.

NMSU researchers also are interested in the use of fire to help treat overgrown forests. The Eagle Creek thinning treatment site is an example of a two-pronged method to lessen fire danger that can be used in some forests near populated areas. Areas that have been thinned also may be treated by broadcast underburns when the conditions are right, which clears out brush and other ground fuels.

"Doing it this way can be a cleansing or rejuvenating process, as opposed to a catastrophic process," Cram said. "That's pretty germane right now. Looking at this winter and seeing very little snow pack or moisture ... that doesn't bode very well for the upcoming fire season."

In other areas where terrain or proximity to homes precludes the use of fire, mechanical thinning may be the only option. Either way, the harvester-forwarder could play a big role.

NMSU scientists will analyze the data they collected on the forest-harvesting machine and expect to publish their findings later this year.
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