Donald R. Currey, An Ancient Bristlecone Pine Stand in Eastern Nevada, Ecology, Vol. 46, No. 4 (Jul., 1965), pp. 564-566
Bristlecone Pine (Pinus aristate Engelm.), the oldest living tree of verified age presently known, is restricted to numerous, rather isolated stands at higher altitudes in the southwestern United States. Stands occur from the Rocky Mountains, through the Colorado Plateau, to the western margin of the Great Basin. Studies in recent years (Schulman and Ferguson 1956, Schulman 1958) indicate maximum sampled tree ages of 700-800 years on Mt. Evans, Colorado; 1,500+ years on the San Francisco Peaks, Arizona; 3,100 years in the Schell Creek Range of eastern Nevada; and 4,600+ years in the White Mountains of eastern California. The last age, from a stand that includes a number of trees over 4,000 years old, is the oldest reported prior to 1965.
In 1963 and 1964, during studies of Recent (Little Ice Age) glaciation and nivation in the mountains of the southwestern United States, stands of bristlecone pine were encountered at several localities. Where feasible, older trees were cored or sectioned (1) to provide minimum absolute ages for glacial and periglacial features on which they are situated, and (2) to possibly provide dendroclimatic histories of the localities. A previously unstudied bristlecone pine stand on Wheeler Peak in easternmost Nevada was found to contain several trees well over 3,000 years old and one which is clearly about 4,900 years old.
Wheeler Peak (13,063 ft), highest peak in the eastern Great Basin, is in the north-south-trending Snake Range, 14 miles west of the Nevada-Utah boundary. The bristlecone pine stand is at the mouth of a deep glacial cirque on the northeast face of the peak within a national forest tract known as Wheeler Peak Scenic Area. The stand is closely approached by a road from Baker, Nevada, a village 10 miles to the east.
The Wheeler Peak bristlecone pine stand, covering approximately 300 acres, ranges in altitude from 9,500 ft to the upper limit of tree growth at slightly above 11,000 ft. Bristlecone pine and Engelmann spruce (Picea En gelnaanini) are codominant in the stand, and limber pine (Pinus flexilis) is an associate. Laterally, the stand grades abruptly into the typical subalpine forest of the Snake Range, in which spruce and limber pine are codominant and bristlecone pine is conspicuous by its absence. The nearest neighboring bristlecone pine stand is 6 miles to the south.
Some of the uppermost trees are situated on bedrock of Prospect Mountain quartzite, but most of the bristlecone pine stand is situated on morainal deposits and talus derived from the bedrock. Interstitial patches of skeletal soil have developed between the quartzite boulders. The region is semiarid. The nearest climatological station, Lehman Caves National Monument, 4 miles east of and 3,000 ft lower than the stand, has recorded (20 years of record) a mean annualprecipitation of 12.8 inches.
To facilitate compilation of a long-term tree-ring chro-nology for the Wheeler Peak area, one of the larger living bristlecone pines was sectioned. This tree, WPN-114, grew at an altitude of 10,750 ft, on the gently sloping crest of a massive lateral moraine of Pleistocene age. The site was relatively stable during the lifetime of the tree, the only appreciable change being an accumulation of avalanche-transported debris so that the present ground surface is about 2 ft above the original base of the tree.
WPN-114 had a dead crown 17 ft high, a living shoot 11 ft high, and a 252-inch circumference 18 inches above the ground. The trunk was of the massive slab type. Bark was present along a single 19-inch wide, north-facing strip. Lateral die-back had left 92%o of the circumference devoid of bark. The southfacing (uphill) side of the tree had been so deeply eroded that the pith was missing below a point 76 inches above the ground (100 inches above the original base). A horizontal slab from the interval 18-30 inches above the ground and a smaller piece including the pith 76 inches above the ground were cut from the tree, and a smoothly finished 2-piece transverse section was prepared. Within the radius sector present in the section, the growth layers, or rings, have a rather uncomplicated concentric arrangement. The tree-ring series contains both distinctively thin (microscopic) rings and difficult-to-count incomplete (locally absent) rings. The two parts of the section overlapped and were readily matched using a long ring sequence common to both. The derived radius measures 2,280 mm to the pith, 100 inches above the original base, and encompasses 4,844 counted rings. Mean ring width is 0.47 mm.
Under low power magnification, annual increments of earlywood and latewood were consistently discernible. Intra-annual (false) rings, which are not regarded as a serious problem among high-altitude bristlecone pines (Schulman and Ferguson 1956), presented no difficulty. It is probable, however, that not every year is represented in the ring series. The Wheeler Peak tree-ring chronology is not yet sufficiently well known to permit reliable detection of annual rings missing in this tree. Allowing for the likelihood of missing rings and for the 100-inch height of the innermost counted ring, it may be tentatively concluded that WPN-114 began growing about 4,900 years ago.
Earlier studies supported a tentative hypothesis regarding the distribution pattern of age limit in bristlecone pine, viz., “. . . that the maximum age in this species is to be found in the westernmost stands of its range, the attainable maximum age tending to decrease eastward”. Since an age comparable to the maximum age at the western limit of the species is now known from Wheeler Peak, Nevada, a locality nearer the center of the geographic range than’ the western limit, the simple hypothesis of Schulman and Ferguson is, at least in part, no longer tenable. Refinement of that hypothesis can come only with more extensive sampling of maximum ages.
Downvalley from a remnant glacieret at the head of the cirque is a morainal complex in which a sequence of Little Ice Age (ca. 2,000 B.C. to the present) episodes is represented. In that part of the bristlecone pine stand that is situated on Little Ice Age deposits, maximum tree ages reflect the ages of the sites. The fortunate location of the bristlecone pine stand at Wheeler Peak with respect to Little Ice Age features, coupled with an attainable tree age greater than the span of Little Ice Age time, makes possible the dating of a sequence of Little Ice Age events.
The presence of WPN-114 (and a number of other trees still living after 3,000 years or more) near the present upper limit of trees suggests that the amplitude of climatic change during the Little Ice Age was such as to cause no great downward displacements of tree limit. Increasing knowledge of the altitude-age composition of the bristlecone pine stand will nevertheless provide insight into fluctuations in environmental stresses that have operated on tree limit and forest limit during the Little Ice Age. Many of the dead bristlecone pines seem to be almost as resistant to decay as the living trees. Millennia-old specimens, now dead, show promise of extending the history of the stand to before 5,000 B.P. Possibly no other living species presents such accessible long-term evidence relating to its biogeographic history and to the environmental histories of its sites. Yet largely unstudied are the bristlecone pine stands in the eastern ranges of the Great Basin. At least 20 of the ranges reach altitudes exceeding 10,000 ft and are known to have or could reasonably be expected to support stands of bristlecone pine. Close scrutiny of those stands seems certain to prove more rewarding than previously suspected.