The California X-disease – forest decline
Charles E. Little
They knew 40 years ago that L.A.’s air was sickening the trees in the nearby hills. Since then, the engines of death have invaded even the wild High Sierra.
They are my mountains, the San Gabriels, the mountains of my childhood. Rising like a great wall, the San Gabriels and the adjoining San Bernardino Mountains separate the Los Angeles basin, the richest agricultural region in the world when I lived there, from the scorching Mojave to the east.
You could walk to the Mojave if you wanted, theoretically anyway — right up and over the mountains, never encountering anybody. All I had to do was scamper out the back of our house, run through a vineyard, sneak past an old swimming pool, and there I was in the Angeles National Forest, a true wilderness. Mostly though, the boys in the neighborhood would just hike up the canyons a ways, where the rancheros had bored the watermines, or we’d scuttle crablike along the hot flanks of the steep, chaparral-covered lower slopes of the mountains, winding through thickets of yucca and manzanita whose sinewy red branches we called ironwood.
But on the rare long-hike days, when we could get a bigger boy to go with us, we’d strap on our canteens and take a trailless route way up to the top of the first line of mountains, cross a fire break, skitter down into a box canyon, trudge up to the next ridge, and there it was–a place so rare, so wonderful, so green, it amazed us. For after surmounting that second ridge, we dropped down into an Eden, a mythic place with huge, widely spaced pines. I know now that they might well have been ponderosas and perhaps Coulters, rising majestically into the great vault of blue California sky. “Whoo, whoo,” we would yell from the dappled forest floor into the cool tree-tops where the jays chattered. It was like a hosanna, made in a cathedral so dreamlike that I had it as a dream for many years, coming back again and again in the way that children’s dreams do.
Now I have returned to the San Gabriels. I could never find that very spot again, I am sure. But I have little inclination to try anyway, for it is likely to be gone–like the dream has now gone. Unlike many places in California, our ponderosa Eden would not have been leveled by a bulldozer, and it is altogether possible that it escaped fire. Its demise would be through another agency–what used to be called (and perhaps still should be) the California X-Disease.
In 1955, some years after my childhood treks into the San Gabriels, a young Forest Service timber-management assistant named Willard Tikkala reported for work in the San Bernardino National Forest. The first time he laid eyes on the piney woods around Lake Arrowhead, California, which is surrounded by the San Bernardino Forest, he knew something was wrong. Unlike the deep, verdant green of the pines up north, these trees seemed yellowish and thin at the crown. No one understood exactly what was the matter, but Tikkala (now a forestry consultant for American Forests) knew it was serious. He and his colleagues began calling it the “X-Disease.”
A year later, another timber-management assistant, James E. Asher, even younger than Tikkala, who was then 30, wrote a paper for his superiors describing the condition. The paper is among the first scientific analyses of what ecologists in Europe and America now call the anthropogenic causes of forest decline–in plain English, all the different ways we are polluting our trees to death. This is how the paper, now a kind of historical document, begins:
“The foliage deterioration, affecting an increasing percentage of the Ponderosa Pine (Pitus ponderosa) forest stands within the Arrowhead Ranger District, has been noted with growing concern. This effect, known as the ‘X Disease’ or Needle Dieback is causing loss of vigor and thus a lessening of annual increments on an alarming number of trees. Though the causative agent is classed as ‘unknown,’ mortality is occurring.”
What Tikkala observed and Asher described–as accurately as anyone since–was something called “chlorotic mottling” in the older, inner whorls of the needles of ponderosa and Jeffrey pines, and to some extent on other conifers. The first evidence of the disease he described as “a faint yellowing in narrow bands along the needles of these whorls,” even though the outer, newer whorls remained green and healthy. Then the affected needles would turn completely yellow and drop off, leaving the tree eventually with only one or two whorls of needles rather than four, five, or six. The effect was a slowing of photosynthesis until the tree died.
Though the paper suggested various possible scenarios, in Asher’s view the cause was obvious–“a heavy concentration of air pollutants borne onto the foliage of the ponderosa pine.” In other words, smog–the smoky-colored “haze” that was even then sliding up the sides of the mountains from Sunland to San Berdu.
It certainly wasn’t the drought (there was a severe one in those days, just as there is now). Drought kills from the top down to the bottom of a tree and from the outside needles to the inside. The X-Disease was killing trees in just the opposite way–from the bottom up and the inside out.
Asher’s paper, together with other investigations of smog effects at lower elevations in the Los Angeles basin, prompted the Forest Service to look into the matter seriously. Much of this work was pioneered by Paul Miller, the now-famous pathologist who took on the research into the X-Disease. Miller, quiet-spoken and modest, with the leathery face and the fitness of one who spends long days afield, told me during my visit to his Riverside, California, office and lab that in his papers and lectures he always gives James Asher credit for the first paper.
Miller’s organized testing of Asher’s theory that smog was being carried into the mountains by prevailing winds and was killing the ponderosas was first reported in 1963. It showed the results of an situ experiment up in the San Bernardino mountains wherein branch chambers were attached to pine limbs on test ponderosas and the effects of filtered air, ambient air, and ozone-charged air were compared. The test showed that the filtered-air limbs got better on X-Disease trees, and the ozone-charged limbs got worse.
Then, in a 1966 study, Miller and his colleagues sought a typical test area where they could observe smog damage over a period of years. The plot they finally agreed on contained 150 ponderosa pines, 50 of which were relatively healthy, 50 of which had moderate X-Disease-type symptoms, and 50 of which were severely afflicted. When they went back for a final look just three years later, nearly half the healthy trees had become moderately affected by air-pollution damage, two-thirds of the trees that had shown moderate damage were now severely afflicted, and of the trees severely afflicted in 1963, two-thirds had died. Taken together, after three years of air pollution, only 28 of the original 150 trees remained healthy and some 36 had died.
That this caused some observers to worry is to put it mildly, for by the mid-’60s the smog had been working on the trees for nearly 20 years.
A later, quite definitive study conducted by Miller between 1973 and 1978 showed that not only had thousands upon thousands of trees died in the mountains, but they were not being replaced. Instead, a whole new kind of forest was taking over–of more resistant conifers. The problem these new trees–incense cedar, white fir, and some others–posed for the regeneration of the original forest, even should the smog suddenly abate, is that the replacement trees are shade-tolerant and shade-making, producing an environment uninviting for ponderosas and Jeffries, which want open spaces and sun.
In many places, Miller told me, “You simply can’t walk through the forest anymore, the trees grow so thickly. Why, in the old days you could ride at a full gallop through the forest with its widely spaced ponderosas and never lose your hat!”
Miller sent me to Lake Arrowhead to take a look for myself. And the trees did seem to be thicker and lower than in the old days when I visited here at my Uncle Don’s cabin on the lake. And dead trees were visible down the slopes, looking toward the smog-shrouded basin, and dying ones at the top of Strawberry Peak.
Trucks, planes, and automobiles–especially automobiles, and especially high-compression-engine automobiles, as they all are these day–are killing the trees for the most part. In the 1940s, I was a borderline JD and owner (well, part-owner) of a hot rod with what was called a “Winfield B” engine, a modified four-barrel Ford Model B with the cylinder head shaved to the maximum extent in order to increase compression, while the cylinders themselves were bored out and fitted with larger pistons so that the combustion chambers were correspondingly enlarged. With a huge, specially designed carburetor sucking air like a ram jet and individual pipes rather than a standard exhaust manifold, the result was like riding an ack-ack gun. It was impossible to drive the car slow. And the engine heat was so intense we had to change the oil constantly, as well as replace blown-out gaskets.
We didn’t know it, of course, but every time we cruised into Bob’s Big Boy in Glendale, going vroom-vroom, the heat in that engine was combining the nitrogen in the air with oxygen, creating oxides of nitrogen that would rise from the parking lot and, along with “VOCs”–volatile organic compounds produced by everything from dry-cleaning fumes to the pine-scented trees themselves–combine in the presence of the hot California sun to make the ozone that would kill the trees we had loved as little children.
Under the influence of puberty, we worshipped high-compression, and we were ignorant of its effects on our Edenic groves. And we remained ignorant. A generation later, you could hardly find a car without a hot-burning high-compression engine. Everybody had become a juvenile delinquent, perforce. The ozone-producing smog, form automobiles and other sources, eventually drove my family from their hillside perch. But the trees could not pick up and move. They had to stay where they were, and cope with the environment we had given them. They could not migrate, for example, to the High Sierras, which we had always thought of as the purest of the pure, the pristine place where God’s creation operated as God intended it to.
And that’s where I went next–to the Sierras. First to visit Trent Proctor, an air-resources specialist for the Sierra National Forest.
Proctor, in his 30s, is from an old California ranching family whose original holdings were in Sierra foothills near Porterville, where in fact Proctor’s Forest Service office is located. Like many Californians concerned with natural resources and the environmental impacts on them–he reveals a curious combination of optimism and despair. Optimism in the sense that human ingenuity can always find an answer to any kind of pickle, but despair that this pickle–air pollution created by an inversion layer above and a solid line of traffic below–might be beyond getting out of. For the ozone, far from being confined to the Los Angeles area, is devastating trees in the lower Sierra Nevadas too. It would seem almost impossible that little agricultural towns spread throughout this large central California valley and along just two highways–the old U.S. 99 and the new I-5 that has taken its place–could produce enough smog to hurt trees in the far Sierra mountains. But they do, and it does.
Said Proctor, as we rode up into the mountains in his green Forest Service van, “We have exceeded our carrying capacity here in California.”
After an hour’s drive, we arrived at a high ridge overlooking the valley. It looked to me–under a winter sun–pretty much like the view of L.A. from Strawberry Peak near Lake Arrowhead. Patches of dead trees were visible on the lower slopes, and on our ridge there was a rather perfect specimen, said Procter, of an ozone-stricken ponderosa we could examine. I had already learned from Paul Miller that when there’s no visible smog in the valleys, the mountain trees are, ironically, at greatest risk–for the lack of visible smog means that the pollutants have risen rather than lying close to the ground.
Procter discussed this too when I observed that it was pretty smoggy down there. “In the summer,” he said, “the inversion lifts, so in the southern Sierra we see ozone injury in trees up to about 7,000 feet, and in the northern Sierra to about 5,000.”
He told me that the ozone travels up the drainages on a daily basis. “Down in the valley, where we’ve traditionally done monitoring, ozone reaches a peak in the afternoon. Without the presence of sunlight at night, the nitrous oxides generated by automobiles gobble up the ozone, actually destroying the ozone molecules. So each night, the air in the valley is cleansed of ozone, but up here in the mountains we don’t have those nitrous-oxide generators. So the ozone resides during the nighttime hours, and the exposure time is longer up here than on the valley floor. That means that lesser quantities of ozone may have more effect.”
An additional reason for the greater impact, Proctor explained, is that during the day, the stomata or pores of the needles close, especially during dry periods, and tend to open at times when ozone is present and can enter the needles via a “gaseous exchange.” Once the ozone is inside, it bleaches–just like Clorox, also an oxidant–the chlorophyll from the needles so that they lose their ability to photosynthesize, and then they drop prematurely. A healthy pine will have up to seven or eight whorls, Procter said. The sickly tree we were examining had only one whorl left on many of its branches. It was a goner. “Eventually, as the tree loses its needles to ozone and other factors play on it, the tree loses its ability to process food, and ultimately it will die.”
My next stop was Sequoia National Park, to visit Dan Duriscoe, who had just completed a survey of ozone damage in the park. Duriscoe, whose degree is in physical georgraphy, told me about his studies during a walk to one of his favorite spots, Sunset Rock, which overlooks a complex of High Sierra peaks and canyons stretching away into the far distance beyond sight of highways and cities on the plain many miles to the west. But not so far west as to allow these mountains to escape the cumulative doses of nighttime ozone.
Here in the park, Duriscoe told me, some 10 percent of trees overall showed some level of ozone damage, even though only one out of a thousand might die from ozone itself. As both Miller and Proctor had explained earlier, the combination of drought and rust and beetles, among other stresses, was likely to take an ozone-afflicted tree before the ozone itself would kill it.
“Of the 10 years I’ve been in this area,” Duriscoe said, “last year the mortality of conifers in general has been the most dramatic. But to point to a tree and say that it died from smog is not really possible.” Still, the ozone is a contributing, if not initiating, factor that Duriscoe and his scientific colleagues in the Park Service would like to see reduced.
Earlier studies in the park have shown that in some of the drainages subject to air-pollution “eddies,” ozone injury has been found on as many as nine trees out of 10. “The whole point of our ozone studies up here,” Duriscoe told me, “is to collect evidence to present at permit reviews and for setting standards for ozone under the Clean Air Act. The standard is now .12 parts per million for ozone, but that’s not sufficient to protect the vegetation. Actually, we should consider a different kind of standard. Instead of a maximum hourly average, we should be concerned with the maximum cumulative dose, since studies have shown that it’s the cumulative effects, rather than a single one-hour pollution event, that eventually weaken the tree and lead to its death.”
Out on Sunset Rock, Duriscoe grew reflective. “Working so much out here alone,” he said, “I get to know these trees individually. There’s a kind of personal camaraderie with them. And I kind of object to reducing things to a statistic for a report, although I do it. I am thinking more along the lines of tree number eight out here on Sunset Rock. The statistics do not really tell you the story. You have to come here and look at the trees one at a time and get know them a little bit, and then you might have a feel for it.”
After I left Sequoia, I drove up to Yosemite for a look around (lots of large patches of dead trees, especially along the road from Wawona to Yosemite West). Yosemite valley itself showed signs of drought, of course, but probably not air pollution.
Then, driving down-mountain due west of Yosemite, I arrived at the headquarters of the Stanislaus National Forest, where I met with John Pronos and John Wenz, plant pathologist and entomologist respectively. Their reaction to the crisis of the X-Disease was a good bit less intense than that of any of the scientists I had interviewed earlier. This was due at least partly, no doubt, to the fact that the Stanislaus and other mid-Sierra forests are at the far end of the ozone gradient, which begins in L.A. and peters out at about Yosemite. For these men, the drought was the thing, and the bugs the drought brought in its wake.
Both Pronos and Wenz had been dealing with tree death around Lake Tahoe, where ozone is present, though its effect is uncertain and probably minor. What is certain is that in Tahoe a third to half the trees in certain stands have died.
“Years ago, we did a very large-scale mortality survey in the Sierra Nevada mixed conifer forest,” said Pronos, “and we came up with a normal mortality of between .1 and .3 dead trees per acre. Now we are well beyond 1.0 dead trees per acre–as much as a 10-fold increase.”
I recalled that Paul Miller had given me a chart he made showing a 10-year moving average of precipitation from the years 1883 to 1990 at Big Bear Dam. Since relative precipitation remains fairly constant throughout the California mountains, Miller’s chart indicated more that just a local situation. The situation it showed was a steady downward trend in precipitation over the past 100 years, which if continued for the next 100 would leave California with the rainfall of the Sahara.
This kind of data is why Pronos and Wenz insist on analyses that feature a combination of factors causing forest decline rather than singling out one or another and emphasizing it in research to the exclusion of others. They are facing what appears to be a drought-and-beetle calamity the likes of which has never before been seen in the state. Stated Wenz, “We’ve never had a drought that has extended quite this long. This is the most tree mortality I have seen.”
Still, in Wenz’s view, as soon as the drought really is over, the Sierra Nevada forests will surely recover. There’s one problem, though. The drought has made the trees relatively immune to air pollution, for they tend to “close down” as a survival strategy in dry times, opening up again when water is present. This physiological attribute may conceal the damage potential of ozone under non-drought conditions. Indeed, if the drought is over, ozone damage, wherever ozone is present in any quantity, may increase markedly.
On the other hand, California has legislated draconian measures to reduce air pollution–limiting the release of VOCs (volatile organic compounds) and oxides of nitrogen with laws regulating everything from the use of lighter fluid in backyard barbecues all the way to mandating electric automobiles. That’s all good news, of course, except that many believe these laws will simply curb the increase of pollutants rather than actually reduce them. Even at their levels of 40 years ago, pollutants changed the forests around Los Angeles, presumably forever.
I was running this sort of thing through my mind in the Forest Service conference room in Sonora when Wenz and Pronos started talking about the trouble with the incense cedar–the kind of tree that has come in to replace the dead ponderosa and Jeffrey pines. They told me that even the incense cedar were dying–all over the Sierra–and they don’t know why. Said Wenz, “The bark beetle does not kill these trees, unless they are going to die anyway. Usually, incense cedar fares well during drought periods, and we’d expect them to be drought-free.”
“But that’s not what’s happening,” said Pronos. “They are dying in very high numbers. It is localized, but the patches are quite widespread–not just on certain slopes or elevations, or in dry or wet soil conditions. There’s just no pattern to explain it away. No papers have been written.” I thought of Bill Tikkala and James Asher at Lake Arrowhead, looking at trees dying in the 1950s and wondering what in the world was happening to their forest.
Meanwhile, back in the San Gabriels, I have taken a sentimental journey up to Mount Wilson to view dead trees. Mount Wilson was in my day the site of the largest telescope in the world and always thronged with visitors. Now the place is largely abandoned, though a few recreational facilities remain. I stood on a rock wall that was cracked and crumbling with neglect, staring down at the smog in the great basin below. My parents would bring me here often, and we could see for miles, clear to Catalina Island.
For many of those years, my father had a job with the All Year Club of Southern California, a tourist promotion and economic development organization that celebrated the glories of our region. One day, just after the end of World War II, my father told me: “Son, people are pouring across the border at the rate of a thousand a day! Think of it!” He and the All Year Club had succeeded beyond their wildest dreams.
Before long, he came to regret the mad rush to make Southern California the postwar growth capital of the U.S. But it was done, and now everyone wonders if it can be undone. This was my Eden, and looking down on the blanket of smog, I realized that it had been decisively trashed. We were so stupid about it, so greedy. The thought struck me then, and it persists, that James Asher’s and Bill Tikkala’s X-Disease is not really an affliction of the trees, but a terrible chronic illness in ourselves.
COPYRIGHT 1992 American Forests
COPYRIGHT 2004 Gale Group