Will Ponderosa Pine Forests Disappear?

Two forest fires ravaged the Jemez Mountains near Los Alamos, New Mexico in the last 20 years. These fires are famous among land managers, scientists, politicians, and conservationists because they marked an unexpected change in forest fire behavior. Larger, similar fires have burned in Arizona and Colorado recently. Yet far from being natural phenomenon, these fires are human creations. These fires are destroying vast swaths of ponderosa pine forests, that probably are not going to grow back.

Many scientists project that ponderosa pine forests in the Southwest may be gone within half a century. A forest type that defines the Southwest could be reduced to small patches or even fade away completely. What is going on in the remote expanse of the four corners states?

Humans have profoundly changed the environment of Western states. Many changes have been gradual and happened over generations so we may not notice them. Each generation takes for granted that the environment today is the way it has always been. We may not see the pervasive damage. Most of the West is a fragile, arid environment, where life has taken hold precariously over millions of years. The heavy hand of humanity has pushed the web of life to the brink of collapse in places.

Twenty-seven million acres of ponderosa pine forest in the West are radically altered by modern people. These forests are unrecognizable from how they were before the 1880s. We know how these forests were from first-hand accounts of people like Edward Fitzgerald Beale who rode his horse through the Southwest in 1857. (He also traveled by camel.) Beale wrote about ponderosa pine forests that were carpeted in knee high grass with big old trees and a mix of younger trees scattered widely below. These were open forests where he could see a long way through the trunks of the trees.

“We came to a glorious forest of lofty pines…every foot being covered with the finest grass, and beautiful broad grassy vales extended in every direction. The forest was perfectly open…” Edward Fitzgerald Beale.

Look at Ponderosa pine forests today. Can you find any that look like what Beale saw?  The Valles Caldera National Preserve in New Mexico has the History Grove which vaguely resembles the forests of yesterday. But all across northern Arizona and the middle elevations of New Mexico and southern Colorado, ponderosa forests are radically changed. These forests have increased in density more than tenfold, from 26 trees per acre in 1883 to 291 trees per acre in 1995.

The forests are thick with young trees, or they are entirely young trees growing close together. They are infested with parasitic mistletoe and they are prone to stand replacing fires. Many scientists doubt the ponderosa pine forest type will still be here in a century as the climate warms and large fires spread. Ponderosa forests will be replaced by shrub thickets and exotic grasses, scrub oaks, and locust.

What happened? In short, people from Europe and the eastern US brought livestock that belong in wet climates to the arid West. These animals and the businesspeople who own them have virtually destroyed the ecology and watersheds of the Southwest.

The Bad Bovine

In 1880, the railroads reached northern New Mexico from the north and the east. While cattle and sheep had been in New Mexico since the Spanish brought them three hundred years earlier, various businesses shipped millions of sheep and cows into the area aboard the railroads. New Mexico had approximately 137,000 cows and 620,000 sheep in the 1870s. After the railroads snaked into the Rio Grande Valley, there were 1,380,000 cattle and two million sheep. These animals were turned loose over the entire northern part of what is now New Mexico and southern Colorado without any regulations.

Since then, livestock numbers have decreased but the damage has already been done and continues. Once grass was devoured by sheep and cows, the forest floor was open to tree seeds and millions of small trees sprouted in the barren soils. (Sheep tear grass up by the roots.) Ecologists can see a pulse of ponderosa pine growth that happened once the grass was devoured. Dense thickets of pine and juniper replaced the grasses. Over time those young trees got taller but many of them tangled in stunted thickets below the old tall trees above. Needles cast off the trees built up on the forest floor. The big old trees that weren’t cut down by loggers (most were), struggled for water.

Let’s go back to the forest before livestock. Grass beds below larger trees allowed a great deal of rain and snow moisture to reach the soil and tree roots. Grass also burns easily and quickly, creating a relatively cool fire that passes through an area with short flame heights. Fires started by lightning or people were common before livestock and nobody fought these fires. They would range for miles and miles until the weather put them out or they reached a natural barrier like a cliff or a river.

Fire strengthened the grasses over time, and it killed many of the small pines that sprouted among the grass. Fire sustained the grass/pine ecosystem for tens of thousands of years. A wide variety of wild animals came to depend on this forest ecosystem and evolved with it.

Once livestock destroyed the grasses, the pine forests became extremely flammable and prone to a new kind of fire. Rather that fast, frequent, low-intensity fires that spread across the grassy forest floor, the pine thicket forests carpeted with highly flammable pine needle beds fostered fire climbing into the treetops, through the ladders of pine thickets.

In northern New Mexico, ponderosa forests often have pinon pine and juniper growing among younger ponderosas. In southern Colorado, these forests often have a great deal of gamble oak in the understory. Pinon and juniper invade the ponderosa zone in the absence of fire.

Bad Chemistry

Not only are the new pine forests prone to extreme fire behavior, they’re also prone to disease and erosion. The pine needles that build up on the forest floor are rich in terpenes, a hydrocarbon that the trees synthesize. It may function as a toxin to prevent animals from eating the trees. In any case, the terpenes change the soil chemistry in the pine forests. When grass prevailed, the needles burned frequently, and the grass had an entirely different effect on the soil chemistry.

The terpene-rich pine needle beds may weaken the trees. Changed soil chemistry may make the trees prone to mistletoe, a lethal parasite. The pine needles also suppress other plants and grasses, and they keep light rain from reaching the soil and the roots.  Thus, the forest grows weaker over time.

Around 1900, the US Forest Service arrived in the Southwest with a mission to extinguish all forest fires. Though they only partially succeeded, they unknowingly contributed to the decline of the ponderosa forest.

The US Forest Service finally understood that fire suppression was damaging forests starting in the 1990s. But correcting the badly damaged ponderosa pine forests over millions of acres is a huge challenge for an agency with inadequate budgets.

The Forest Service also did a great deal of good when they arrived in the Southwest. They regulated livestock grazing and reduced numbers of cattle and sheep. Even so, cattle still overgraze the national forests to this day.

 Fixing the Mess

The land management agencies have two ways to restore ponderosa pine forests. They can light prescribed fires when conditions will lead to high mortality among younger trees. This is the least expensive and the most ecologically beneficial tool in the agency toolbox. But given the degraded structure of these forests this is very hard to achieve. Burning the forests hot enough to kill thickets means setting fires that are very active and tricky to control. Yet if the forests are burned at a low intensity, when they are relatively wet, then the fire is too cool to kill the younger pines.

Because the thickets of pines that grew under the larger trees are so tall after a century, most agencies are cutting the young pines out with saw crews. This is known as “mechanical thinning”. It works, and the small trees cut out can be scattered on the ground and burned or they can be removed to make stove pellets or other products. Prescribed fire follows mechanical thinning. Mechanical thinning is expensive for the agencies, but it creates jobs.

Thinning means removing younger, excessive regeneration. Though heavy-handed, thinning helps reset the forest to a point where it can rebalance with frequent low severity fire. Sometimes the Forest Service will allow large trees to be cut too during a thinning operation. Cutting larger trees is logging, not thinning. If anything, logging makes the ponderosa forest imbalance worse.

Looking Back

Today we are dealing with large areas of ponderosa forest in very poor condition because of things people did before the land was managed by any agency. The profit driven livestock operators made money shipping meat out of the Southwest, while costing society hundreds of millions of dollars over time. The costs are burned communities, lost topsoil, lost wildlife, unproductive forests, and forests permanently reduced to brush fields.

The early Forest Service with their “suppress all fires” mentality believed they were protecting future timber stands and they allowed livestock grazing to continue because ranchers had political power and the power to run the early rangers out of town if they over-regulated. In overriding eons-old natural processes in favor of experimental forestry practices and livestock grazing when no native animals exerted remotely similar pressures on the land, they started ripples that turned into tidal waves over time.

Today federal agencies in the Southwest understand very well the predicament they face in the declining ponderosa pine forests. Public lands ranching is slowly dying, but the era of megafires is upon us. Time is short to restore these forests and prepare for the rough times ahead.