About Pinus longaeva D.K.Bailey
Pinus longaeva D.K.Bailey, commonly called Great Basin bristlecone pine, is a medium-sized tree that reaches 5 to 15 m (16 to 49 ft) in height, with a trunk diameter of up to 2.5 to 3.6 m (8 to 12 ft). Its bark is bright orange-yellow, thin and scaly at the trunk base; ancient trees often have gnarled, stunted growth especially at high altitudes, with reddish-brown bark marked by deep fissures. As trees age, much of their vascular cambium layer can die, and very old specimens often only have a narrow strip of living tissue connecting roots to a small number of live branches. Its needles grow in fascicles of five, are stout, and measure 2.5 to 4 cm (1 to 1½ in) long. The outer needle face is deep green to blue-green, while stomata are restricted to a bright white band on the inner needle surfaces. This species has among the longest leaf persistence of any plant, with some needles remaining green for up to 45 years. The cones are ovoid-cylindrical, measuring 5 to 10 cm (2 to 4 in) long and 3 to 4 cm (1 to 1½ in) wide when closed. They start out green or purple, and ripen to orange-buff at 16 months old. Cones have numerous thin, fragile scales, each with a bristle-like spine 2 to 5 mm (1⁄16 to 3⁄16 in) long. When mature, cones open to 4 to 6 cm (1½ to 2½ in) wide and release seeds immediately after opening. Seeds are 5 mm (3⁄16 in) long, with a 12 to 22 mm (½ to ⅞ in) wing. Most seeds are dispersed by wind, but some are dispersed by Clark's nutcrackers. The common name 'bristlecone pine' comes from the dark purple female cones that bear incurved prickles on their surface, and the green needles give twisted branches a bottle-brush appearance. Great Basin bristlecone pine can be distinguished from related species: it differs from Rocky Mountain bristlecone pine because its needles always have two uninterrupted resin canals, so it lacks the small white resin flecks characteristic of Rocky Mountain bristlecone pine needles. It differs from foxtail pine because its cone bristles are over 2 mm (0.079 in) long, and its cones have a more rounded, rather than conic, base. This species occurs in Utah, Nevada, and eastern California. In California, it is restricted to the White Mountains, Inyo Mountains, and Panamint Range in Mono and Inyo counties. In Nevada, it grows in most of the higher Basin and Range ranges, from the Spring Mountains near Las Vegas north to the Ruby Mountains. In Utah, it occurs northeast to South Tent in the Wasatch Range. Many sites occupied by this species are inaccessible, so current information on their location and abundance is incomplete and additional data collection is needed. Environmental niche modelling using topographic and spectral variables processed in a geographic information system (GIS) has been used to improve mapping of the species' distribution. This tree grows in large open stands, unlike the related foxtail pine which sometimes forms dense forests. Pinus longaeva generally does not form closed canopies, with tree cover usually only ranging from 15% to 50%. It shares habitats with multiple other pine species, including ponderosa pine, white fir, and notably limber pine, a similarly long-lived high-elevation species. It is a vigorous primary succession species that grows quickly on new open ground. However, it is a poor competitor in good-quality soils, and grows best in harsh terrain. It is often the dominant species in high-elevation dolomite soils, where very few other plant species can grow. Bristlecone pines are protected in a number of areas owned by the United States federal government, such as the Ancient Bristlecone Pine Forest in California's White Mountains and Great Basin National Park in Nevada. These protected areas prohibit cutting or gathering of bristlecone pine wood. While direct observations of Clark's nutcrackers foraging on Pinus longaeva seeds have not been reported, evidence suggests the birds play a role in seed distribution. Clark's nutcrackers use conifer seeds as a food resource, storing many seeds underground for later use; some of these stored seeds are never retrieved and can germinate into new plants. Multiple seeds often germinate together from stored caches, which produces the multi-trunk growth form commonly seen in Pinus longaeva in areas where Clark's nutcrackers are present. This high prevalence of multi-trunk individuals supports the conclusion that the birds disperse the species' seeds. An introduced fungal disease called white pine blister rust (Cronartium ribicola) is believed to affect some individual trees. The species was first placed on the IUCN Red List in 1998, where it was listed as Vulnerable (threatened). However, a 2011 population survey found that the overall Pinus longaeva population is stable, and no known subpopulations are decreasing in size. White pine blister rust was also found to have a negligible effect on the overall population, so the species' status was changed to Least Concern. In terms of fire ecology, the tree is extremely susceptible to fire, and is damaged even by low-intensity burns. Its resinous bark ignites quickly, and a crown fire will almost always kill the tree. Despite this individual susceptibility, Pinus longaeva populations are known to be extremely resilient, and as a primary succession species, populations are expected to reestablish quickly after a fire. Large-scale fires are extremely uncommon in the areas where this species grows, so fire is not a major factor in the species' long-term viability. Historically, Pinus longaeva stands have experienced fires ranging from low to high severity, and fuel structures vary considerably across elevational gradients. At low elevations in mixed-species stands, fuels are often heavy and located close to anthropogenic ignition sources. At high elevations near treeline, Pinus longaeva typically grows on limestone outcroppings that provide little to no surface fuel to spread wildfire. However, warmer temperatures are expected to lengthen the fire season, which could increase fire frequency in low and mid-elevation Pinus longaeva systems, where stands are typically denser and surface fuel is most abundant. While large destructive wildfires are rare, events like the 2013 Carpenter 1 fire in southern Nevada and the 2000 Phillips Fire in Great Basin National Park — which started in lower elevation fuel types and spread through tree crowns with the help of extreme fire weather — could become more likely in the future.
