Thinned Forest May Help With Moisture


Conventional wisdom holds that forest thinning is a good thing. But the number of studies to prove that is somewhat limited.

That's why a forest health study being conducted in the Manzano Mountains by SWCA Environmental Consultants could be of lasting importance.

David Lightfoot of SWCA gave a presentation at the annual Estancia Basin Resource Association meeting on Jan. 12. He shared some of the results so far on the study, which is in its fifth year of hopefully 10 years that will be studied. From the outset, the good news seems to be that thinned areas of the forest have a positive impact on the watershed.

"The thinning is resulting in higher moisture content in the soil," Lightfoot said.

He said the best guess as to increased moisture content may be because of the thinning methods used. He explained that in the 20 sites chosen in the Manzanos each have a "treated" and "control" area.

The study started in 2007 by collecting baseline information on current conditions. Three years ago, areas within the sites were thinned and SWCA has been studying the impact ever since.

Treated areas are thinned using government guidelines, which include laying down a layer of mulch in the thinned areas. In control areas, nothing is done so that researchers have a comparison for the treated area.

Lightfoot said the mulch could be trapping more moisture in the soil, and that this theory will be proved out in the next couple of years as the mulch becomes part of the soil.

Another positive thing seen during the study is that there is greater water runoff from rain and snow in the treated area, which, in turn, means more water recharging the aquifer. Because of the small size of the study areas – each study area is less than five acres – Lightfoot said he doubts that there will be much of an impact of the Estancia Valley's aquifers. But that doesn't mean thinning on a larger scale wouldn't be helpful, he added.

Lightfoot said that the moisture content and runoff results so far have been somewhat surprising seeing as New Mexico has been in a severe drought since the study started.

"We haven't seen the snowpack or the precipitation we would have normally expected, so we were a bit surprised at the moisture content," he said.

Still, that the drought is occurring could bear some interesting fruit for the study, he said.

One interesting aspect of study areas is looking at that hasn't seen much change is the frequency of wildlife in the study areas and new plant growth.

Lightfoot said that there hasn't been much difference between the wildlife detected in the treated areas as opposed to the control areas. For instance, the occurrence of birds and small animals are about the same. He did note that livestock and other grazing animals do like the openness of the thinned areas.

It's the livestock that is causing some issue for measuring new plant growth, he said. Because the study areas are on private land, livestock has regular run of the tracts. The researchers believe that there has been new plant growth, but that it has quickly been eaten by grazing animals.

"It's just one of the things we have to deal with," Lighfoot said.

However, the new plant growth has been of native plants and grasses.

Right now, there are a lot of questions about what is going on in the study areas, Lightfoot said. But he explained that in relative terms, it is still very early in the study. He said researchers are hoping the study can be funded for at least another 10 years.

"This is a long-term study and we hope we'll be able to see it through," he said.

The study is being funded by the New Mexico Water Trust Board and overseen by the Estancia Basin Watershed Health, Restoration and Monitoring Steering Committee, which is comprised of the Claunch-Pinto, Edgewood and East Torrance soil and water conservation districts; New Mexico State Forestry and the New Mexico Environment Department.