Habitat and Ecology
Great Basin BristleconePpine occurs in montane, subalpine, and timberline communities. It occurs in pure stands, but is also frequently codominant with Limber Pine (Pinus flexilis). Other associated species, depending on geographic location and site characteristics, include Single Leaf Pinyon (Pinus monophylla) at lower elevations, Quaking Aspen (Populus tremuloides) on mesic sites, and Engelmann Spruce (Picea engelmannii), Subalpine Fir (Abies lasiocarpa), Rocky Mountain White Fir (Abies concolor var. concolor), and Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) in eastern Nevada and Utah.
The understorey in Great Basin bristlecone pine communities is typically sparse. Shrub associates include Big Sagebrush (Artemisia tridentata), Low Sagebrush (Artemisia arbuscula), Wax Currant (Ribes cereum), Curl-leaf Mountain Mahogany (Cercocarpus ledifolius) and others. Common associated herbaceous species include Prairie Junegrass (Koeleria macrantha), Bottlebrush Squirreltail (Elymus elymoides), King’s Sandwort (Arenaria kingii), and Granite Prickly Phlox (Leptodactylon pungens). In general, stands become increasingly diverse eastward through the range of the species, with a corresponding decrease in altitudinal range. Overall, plant diversity in these Bristlecone Pine communities is greater on limestone-derived soils than on quartzite-derived soils.
Great Basin Bristlecone Pine has the longest life span of any nonclonal species in the world. It is believed that the longevity of Bristlecone Pines is directly related to site adversity, with a high proportion of dead: live wood reducing respiration and water loss, thereby extending the life span of the tree. A relationship between tree age and proportion of dead stemwood suggests that the great ages of some individuals are related to their capacity to survive partial die-back while maintaining a constant ratio of photosynthesizing and non-photosynthesizing live tissue. In addition, high-elevation, arid environments are poor habitats for insects and root-decaying fungi that might otherwise reduce the life span of these ancient trees.
Great Basin Bristlecone Pine communities are highly drought-tolerant, generally found on very dry, mid- to high-elevation exposed slopes and ridges, with no evidence of Pleistocene glaciation. Slopes are typically steep, ranging from 10% to 50%. Stands are typically very open at high elevations, with a sparse understory. At lower elevations, Great Basin Bristlecone Pine is generally found in denser, mixed forests. Great Basin Bristlecone Pine is shade intolerant and cannot establish in very dense forest environments. Canopy cover may range from approximately 15-50%, with more open stands on harsher higher elevation sites containing massive multi-trunked trees, and tall upright trees with more tapered single trunks characterizing lower elevation sites with higher canopy density.
Soils are shallow lithosols, usually derived from limestone or dolomite, though occasionally sandstone or quartzite soils support Great Basin Bristlecone Pine. Great Basin Bristlecone Pine is found in arid climates with cold winters and droughty summers. Annual precipitation ranges from 300-600 mm, with temperatures as low as -18°C in January to 34°C in July.