Conifer die-off increases threat of wildfire
In the past few years, New Mexico has experienced huge, record-breaking fires in both the Jemez Mountains and the Gila National Forest. Big fires haven’t hit the Sandia district of the Cibola National Forest to the east of Albuquerque. But thousands of acres of dead conifer trees pose a hazard. That’s because after the trees die and dry out, they provide fuel for wildfires.
Silviculturists like the Sandia District’s Shawn Martin practice a specialty within forestry, managing forest health by paying attention to everything from tree sizes to insect types.
Insect outbreaks are a massive problem in southwestern forests, where drought and overgrowth have weakened millions of acres of trees. Two years ago, the Forest Service conducted aerial surveys over 21 million acres, and while the number of acres affected by new insect-related dieoffs was down from the previous year, it’s still high: Ponderosa-type bark beetles defoliated 70,110 acres in New Mexico; mixed conifer-type bark beetles, 66,620 acres; spruce-fir type bark beetles, 21,550 acres; and western spruce budworms killed more than 300,000 acres.
Such a challenge requires vigilance, which is why on a cloudy morning last October, Martin headed up the west face of the Sandia Mountains. About 10 miles above the Village of Placitas, he stopped to check an insect trap hanging from a tree alongside the gravel road. Bugs fill the sticky interior of the cardboard triangle; it’s part of an early warning system for Douglas fir tussock moths.
Over the past five years, those moths and fir engraver beetles have hit the higher elevations, while the piñon ips beetle infested lower elevation trees.
All told, there are about 9,000 acres of dead conifers in the Sandias.
According to Andy Graves, the district’s entomologist, these native insects did what comes naturally in an overly dense forest that hasn’t seen fire in decades and is experiencing drought: They took advantage of stressed and weakened trees.
While the insect infestations have declined with wetter conditions, the dead trees and overgrown brush still pose problems.
That’s obvious when Martin tries to hike toward some of the largest stands of dead trees. New Mexico locus, oaks, and chokecherries, along with miscellaneous prickly and stickery plants block the way. Chickadees and Northern flickers call from the thickets.
Had the forest been thinned, he says, or natural fires burned here over the past century, the trees would have been more resilient when the drought crept in beginning in the late 1990s.
Next, the Forest Service hopes to treat about 16,000 acres in the Sandias. This project would, in some places, overlap with the dead conifers. The proposed plan, called La Madera Landscape Restoration Project, would hopefully restore the forest to healthier historic conditions.
There's no one plan for the entire forest. Rather, individual areas or stands of trees call for different methods depending on where they are, what types of trees are growing there, and factors like how steep the slopes are and if access roads are nearby. The suite of tools available could include prescribed fire, hand-clearing of thickets and debris, and where possible, mechanical clearing.
“As an agency, we’re trying to restore historic conditions to provide resiliencies for when fires do come,” Martin says. “We try to restore those conditions, to have uneven ages (of trees) and for there to be gaps between trees. However, nowadays, there are too many smaller trees, in the range of five to 18 inches in diameter."
But they still have a long way to go through the National Environmental Policy Act, or NEPA, process. If everything goes according to plan, the district might receive a final decision by the end of this year or early 2017. Only after that can crews get out into the forest.
Pine, juniper forests predicted to disappear
Recently, scientists from Los Alamos National Laboratory, Columbia University, the University of New Mexico and a pile of federal agencies and universities published a paper in the peer-reviewed journal, “Nature Climate Change" that predicts the disappearance of the Southwest's pine-juniper forests.
It follows a 2010 paper about how warming is affecting southwestern forests and another in 2012 that found 20 percent of the region’s forests had been affected by beetle infestations and high-severity wildfires since the late 1990s.
In the new study, scientists simulated drought conditions to see how evergreen trees will respond to warming in the coming decades. Over five years, they studied how trees perform certain functions, like photosynthesis and the absorption of water during drought.
They found that earlier mortality estimates were too low—and projected that by 2100, pine-juniper forests in the southwestern U.S. will be gone and more than half the evergreen trees in the northern hemisphere will have died.
That large-scale die-off may have global impacts.
As the authors point out, forests absorb carbon. If tree die-offs continue at this rapid rate — exacerbated by warming temperatures and more extreme drought events — that carbon absorption function could be diminished enough over the next century to further accelerate warming.