By Tom Oberbauer
In a relatively obscure area of Anza-Borrego Desert State Park is a mountain range called the Pinyon Mountains. It is far from any habitations and except for one dirt 4-wheel drive road, it is pristine. It has not been affected by human impacts other than the typical non-native species that inhabit all Southern California deserts and it has not had records of fires, fire suppression, or vegetation management of any kind. It is difficult to get to this area.
Pinyon pines form large forests in the San Bernardino Mountains, the San Jacinto Mountains, and the Sierra Juarez south of the border, but in San Diego County, they are much more limited. The Pinyon Mountains in San Diego County consist of an elevated range with an east-west trending valley at roughly just under 4,000 feet (1,209m) with a ridge of 4,400 feet (1,330 m) on the north side and a series of ridges on the south that range from 4,400 to 5,300 feet (1,209 m to 1,600 m). Whale Peak at 5,347 feet (1,616 m) is the highest point. Two major canyons drain into the valley from the ridges on the south side. Pinyon pines grow in open woodlands and forests on the north slopes of both the north ridges and south ridges and the pines extend down the canyons into the valley bottom in low numbers. From Google Earth, it appears that there was roughly 900 acres (350 hectares) of Pinyon Pine woodland/forest. It is or was of respectable size but perhaps not large enough to support pinyon species like Pinyon Jays. I was able to visit it a few times in the 1980’s and 1990’s, parking in the valley and hiking up onto the ridge to the south, though I never attempted to climb Whale Peak. The forest of Pinus monophylla (Single leaf pinyon) on the various levels of the ridges south of the valley was relatively dense and provided a good impression of how unique and striking the vegetation was.
During the extended dry period in the 1980s and again in the early 2000s, when large numbers of pines in San Diego County perished, Pinus coulteri on the south eastern end of Palomar Mountain and Pinus jeffreyi in the area around Julian, it seemed that the desert mountains were not affected.
Pinus monophylla (above; Photo from Calscape) grows in areas that receive between 8 and 18 inches of precipitation (Zouher 2001), and can grow for 350 years, but most are younger than 150 years. They are considered the most drought tolerant of all pines. They are dispersed by animals carrying the seeds and caching them where they can germinate when forgotten by the animals, including jays, chipmunks or squirrels. They are also slow growing, only two meters tall in 60 years and 150 years to reach 28 feet in height. Pinus monophylla (left; Photo from CalFlora) grows in areas that receive between 8 and 18 inches of precipitation (Zouher 2001), and can grow for 350 years, but most are younger than 150 years. They are considered the most drought tolerant of all pines. They are dispersed by animals carrying the seeds and caching them where they can germinate when forgotten by the animals, including jays, chipmunks or squirrels. They are also slow growing, only two meters tall in 60 years and 150 years to reach 28 feet in height.
While it is possible that the Pinon pines in the Pinyon Mountains were dispersed there by animals across the desert floor, it is more likely that they are part of a population that has occurred there for thousands of years, probably back to the Pleistocene, when they would have grown at much lower elevations and there would have been opportunities for continuous forests and woodlands of Pinus monophylla.
Southern California has endured many droughts, including those already mentioned, but very severe drought has occurred in the desert more recently. While coastal mountain slopes and coastal mesas have had rainfall seasons that are significantly below normal, desert regions inland have suffered greater reductions of precipitation. When San Diego International Airport has had 40 or 50 percent of normal precipitation, such as the current 2021 season, the Anza-Borrego Desert has had 32 percent of normal. Between 2012 and 2017, accumulated percentage loss was very high. That drought was significant throughout the entire Western United States, just as the 2021 dry season.
It had been many years since I hiked up to see the Pinyon pine forest on the main mountain range. In December of 2020, a visit to one of the large canyons that trend to the north side of the ridge, illustrated a loss of at least 30% of the trees, but in the canyons themselves, there were still good numbers of healthy trees. The trees in the bottom of the valley were still apparently healthy as well. However, a glimpse of the ridge just south of the valley gave the impression that a larger number of trees died in the upper areas. It seemed that a hike up onto Whale Peak, farther up into the center of the forest was warranted. In preparation for the hike, I examined and observed photographs that hikers posted on the AllTrails web site and videos posted on YouTube. People who hiked up the mountain during and after 2016 made comments about the low numbers of living pinyon pines on the route up to the peak. Photographs from hiker’s trip logs from 2011 showed the trees still growing, but after that, the numbers of live trees seemed to fall. It did not seem possible to me that the statement as quoted by one of the hikers “all of the trees were dead” could be correct.
I drove up into the valley in January following a snowfall and several inches were present on the valley floor. Then again in March on a warm, clear day, expecting to take assessment on how many trees were really lost and how many survived.
While two of the canyons that drain into the valley floor still had numbers of trees growing, I was absolutely shocked at the amount of forest on the upper slopes that was actually dead. It appeared to be more than 90% dead. Vast forests of trees were leafless and dead, clearly having died a few years ago. Individual trees that were still alive were rare and finding more than one was limited to a few locations. The area turned from being a beautiful, green forest of living trees into a ghost forest of dead, gray and blackened stems.
The trail first climbed up a narrow wash with large type Nolina parryi scattered on the slope and in flower. They usually are seen while growing with a rosette of leaves on or near the ground but with tall flowering stalks with orange, brown colored inflorescence. However, one in this canyon had a tall trunk that was approaching three meters in height.
The variety of plants increased when I saw Ephedra aspera (Boundary ephedra) and Bernardia incana (Western bernardia), a low shrub with small, oval, greenish brown leaves both growing very commonly on the slopes and flatter areas. Quercus cornelius-mulleri (Desert scrub oak) was also growing on the slopes of the canyon. The climb through that canyon over large boulders and rocks, mostly allowed one to stay standing, but occasionally required the use of hands to balance one’s self. The rocks are old, weathered granitic of grayish tan color. Cylindropuntia ganderia (Gander’s cholla) grew along the slopes and in a wide variety of other locations on the way.
Above the canyon on the north slope was a flat valley with another higher north facing slope on the south side of that upper valley. A few pinyon pines were still living around the edge of this valley bottom. It was not really a meadow because it lacked grassy cover, but as a flat bottom it had low Bernardia shrubs and sandy openings. Juniperus californica (California juniper) trees, were growing in various locations and did not seem to have been as seriously affected by the drought because they were mostly alive.
The oddly flowered Thamnosma montana (Terpentine broom) was growing along the way. The flowers (above; photo credit Calscape) are strange bluish-purple elongated structures with small openings on the end, appearing like elongated vases. The fruits are connected to dual, round structures.
Ambrosia salsola (Cheesebush), and Ephedra aspera (Boundary ephedra; below) were also growing there.
The trail to the peak passed along the edge of the valley bottom before climbing up again on this north slope.
It was here that the shock of the magnitude of the death of the forest became truly apparent. The north slope trail climbed through mostly dead trees with only a few live trees. Shiny black Phainopeplas with flashes of white wing patches and red eyes flew by, making their “switt” whistley call.
Arctostaphylos glauca (Bigberry manzanita). Photo credit: Tom Oberbauer.
Farther up the slope, I came across a very large Arctostaphylos glauca (Bigberry manzanita; above). Large portions of it were dead, indicating that it also must have suffered the adverse effects of the drought period that killed the pines; however, the portion that was still alive was flowering profusely and buzzing with bees. Other plants present were Cercocarpus betuloides (Mountain mahogany); Ericameria pinifolia (Pine goldenbush) with bright green needle-like leaves; and a few Chaenactis stevioides (Desert pincushion) represented this year’s annual plant crop, but the plants were not very dense since the rainfall has been very low this season. Tiny examples of Lomatium mohavense (Mohave lomatium) with finely divided, ferny like leaves were also growing. White flowered Mirabilis laevis var. villosa (Hairy wishbone plant) was growing along the trail, as well as Pellea mucronata (Bird’s foot fern) and Sphaeralcea ambigua var. ambigua (Apricot mallow).
Other shrubs on the slopes included Ericameria linearifolia (Narrowleaf goldenbush) with long, green needlelike leaves; Prunus fremontii (Desert apricot: below) with its rounded, flattened leaves and cream or pinkish-cream flowers; Opuntia basilaris (Beavertail cactus); and Salvia apiana (White sage).
Annuals that were growing farther up included the blue flowered Phacela distans (Wild heliotrope) and Salvia columbariae (Chia; below). The Chia, with purplish flowerheads and green crinkly divided leaves, was dwarf. Skeletons from last season were three times the size of these plants. Rhus aromatica (Skunkbrush) also grew there.
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The rest of the hike up was similar. Occasional groups of living trees existed on the way to the peak, mostly three or fewer trees.
Whale Peak top with a couple of live trees. Photo credit: Tom Oberbauer.
At the highest point, a few trees were growing as well. From the peak, views to the north extend to San Jacinto past the Santa Rosa Mountains and the Laguna Mountains created a dark chaparral covered wall on the west. South of the peak, the slope is so steep that it appears like a cliff. One of the closest larger Pinus monophylla forested areas exists on the northeastern slopes of the Santa Rosa Mountains in the community of Pinyon Pine. A visit to that area recently indicated that the trees generally appear to be healthy and growing. A few scattered individuals were dead. The canyons that lead down into the desert from the woodland areas that support Pinus monophylla appear similarly not to have been significantly affected.
The overall issue of drought caused die off of Pinus monophylla in other parts of the West began before 2008 (Greenwood and Weisberg 2008) and other species of pinyon pine, including Pinus edulis (Two needle pinyon pine), suffered losses from drought (Meddens et al. 2013; Clifford et al, 2013). As described above, the major loss of the pines in the Pinyon Mountains appears to coincide with a regionwide drought of enormous significance throughout the Southwest from 2012 to 2016. However, a recent study (Hantson et al, 2021) examined the change in vegetation density within a portion of San Diego County that includes much of the Anza-Borrego Desert State Park, including the Pinyon Mountains and the Peninsular Ranges. Using remote sensing data over the past 40 years, a reduction in overall density of vegetation in the study area was documented, and it was especially pronounced in the drier portions of the study area. Furthermore, they analyzed the correlation of vegetation loss with precipitation loss and drought. They found that drought alone was not significant enough to explain the reduction in vegetation but that warming temperatures appeared to be better correlated with the vegetation change than precipitation alone. The record temperatures of the current and past summers for high temperatures in the region but particularly the number of days in the desert areas that have exceeded 120o F provides a small glimpse into the existence of the warming problem on top of the cumulatively higher temperatures that have occurred year to year in this area. The decimation of an entire forest that has probably grown in the Pinyon Mountains for thousands of years is another graphic illustration of the impact of climatic change that has already occurred.
References
Clifford, M. J., Royer, P. D., Cobb, N. S., Breshears, D. D., and P. L. Ford. 2013. Precipitation thresholds and drought-induced tree die-off: insights from patterns of Pinus edulis mortality along an environmental stress gradient. New Phytologist (2013) 200: 413–421. Greenwood, D. L. and P. J. Weisberg. Density-dependent tree mortality in pinyon-juniper woodlands. Forest Ecology and Management 255 (7): 2129-2137 Hantson, S, Huxman, T. E., Kimball, S., Randerson, J. T. and M. L. Goulden. 2021. Warming as a driver of vegetation loss in the Sonoran Desert of California. JGR Biogeosciences 126 (6) Warming as a Driver of Vegetation Loss in the Sonoran Desert of California - Hantson - 2021 - Journal of Geophysical Research: Biogeosciences - Wiley Online Library Accessed August 2021 Meddens, A. J. H., Hicke, J. A., Macalady, A. K., Buotte, P. C., Cowles, T. R. and C. D. Allen. 2014. Patterns and causes of observed pinon pine mortality in the southwestern United States. New Phytologist 206 (1):91-97. Patterns and causes of observed piñon pine mortality in the southwestern United States - Meddens - 2015 - New Phytologist - Wiley Online Library Accessed August 2021 Zouher, K. L. 2001. Pinus monphylla In: Fire Effects Information Systems (online). U. S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer) Available at: https://www.fs.fed.us/database/feis/plants/tree/pinmon/allht ml accessed May, 2021.