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Dark times for NM evergreens?

SANTA FE – What would New Mexico’s high desert look like without piñon and juniper trees dotting the hillsides?

According to a new scientific study, New Mexicans might come to live amid such a landscape, virtually barren of all coniferous trees, within a generation or two.

The study, led by a Los Alamos National Laboratory researcher, says the conifers of the southwestern United States’ pine-juniper woodlands could be wiped out by climate change. “What we found is that by 2050, give or take multiple decades, there should be no forests in the Southwest,” said Los Alamos ecologist Nate McDowell.

 MCDOWELL: Tested stressed trees for mortality

MCDOWELL: Tested stressed trees for mortality

McDowell is lead author of a paper published Monday by an international team in the journal Nature Climate Change.

This study focused on the lower-altitude, more drought-tolerant piñon and juniper trees. Earlier LANL research at the lab produced similar, broader findings for forests including higher altitude trees like ponderosa pine, and there are already “wipeouts” at higher elevations, McDowell said.

The grim study comes in a year when one of New Mexico’s wettest years on record has erased, for now, drought conditions from virtually the entire state map.

The paper says the survival mechanisms of Southwestern trees will accelerate their own demise if the long-term pattern of higher temperatures and drought continues.

To prevent water loss, a coniferous tree closes the stomata – openings in the needles that take in gases. But closure also prevents the trees from taking in carbon dioxide, the tree’s food source, and stops photosynthesis, the process by which plants convert sunlight to fuel for life. And leaving more carbon dioxide in the air just makes the atmosphere warmer.

“So it’s like a thermostat gone bad – the warmer it gets, the more forest we lose, the forests are then not taking up CO2, so the warmer it gets,” McDowell says in a video interview provided by LANL. “So it feeds back on itself. This is the threat we are concerned about.” Carbon dioxide emissions make up most greenhouse gases that hold heat in the earth’s atmosphere.

New Mexicans have seen major losses of piñon trees in the recent past due to a combination of drought and bark beetles, which are able to penetrate the trees after water shortages cause a loss of protective resin. But even hardy junipers are in line for a die-off, McDowell told the Journal .

A piñon in northern New Mexico, seen in 2002, that was killed by a combination of drought and bark beetles. (Josh Stephenson/Journal)

A piñon in northern New Mexico, seen in 2002, that was killed by a combination of drought and bark beetles. (Josh Stephenson/Journal)

“For us locals, the junipers never die, right?” he said. But in the new study, he said “the prediction is junipers are in trouble, and that surprised us.”

The new study combines field experiments, which were used to produce updated modeling, and comparisons to other research.

In five years of field research, the team found that depriving trees of about 50 percent of usual precipitation – at a plot near Socorro, according to McDowell – led to 80 percent mortality among mature piñons and 25 percent for junipers. Another tree site near Los Alamos has been monitored for more than two decades.

The on-the-ground research provided empirical information for new regional models of the impact of drought and higher temperatures, said to be state-of-the art, and compared these regional models with global simulations. The global predictions aren’t as severe but still confirm “widespread conifer loss” in this century.

The study says that averaging the regional models shows that 72 percent of the Southwest’s needleleaf forests “will experience mortality by 2050, with nearly 100% mortality of Southwest USA forests by 2100.”

McDowell noted that the study didn’t take into account that pockets of trees isolated from insects or fire might last longer. But, on the other hand, wildfires, a constant in the Southwest in recent years that could accelerate forest loss, also weren’t factored in.

What would replace piñon and juniper?

Probably grass, gambel oak and creosote bushes, McDowell said.