Pinyon–juniper woodland

Pinyon–juniper woodland, also spelled piñon–juniper woodland, is a biome found at higher elevations near deserts in the Western United States, characterized by being an open forest dominated by low, bushy, evergreen junipers, pinyon pines, and their associates which vary from region to region.[1][2] The woodland's density and crown height varies dramatically depending on a variety of factors, with mature trees ranging in height from as low as 2 meters[3] up to 15 meters.[4] At lower elevations, junipers often predominate and trees are spaced widely, bordering on and mingling with grassland or shrubland. As elevation increases, pinyon pines become common and trees grow closer, forming denser canopies.[3] Historically, pinyon-juniper woodland has provided a vital source of fuel and food (particularly piñon nuts) for peoples of the American Southwest.[3]

Single-leaf pinyon–Utah juniper woodland in northeastern Nevada near Overland Pass at the south end of the Ruby Mountains

Major types

Pinyon-juniper woodland has three major types: pinyon-juniper savannah, pinyon-juniper wooded shrubland, and pinyon-juniper persistant woodland.[2] Pinyon-juniper savannahs are dominated by grasses and forbs, with dense undergrowth and savannah-like sparser trees. Monsoon summer rains are common in pinyon-juniper savannahs, since they favor the growth of warm-season grasses. Common grass species are blue grama, other species of grama grass, new mexico muhly, curlyleaf muhly, and needle and thread grass. Pinyon-juniper wooded shrublands are transition zones where pinyon-juniper woodland is expanding or contracting, often bordering other vegetation types. In absence of fire, they shift from grass and forb-dominated, to shrub-dominated, to tree-dominated communities over time. Common shrub species are big sagebrush, other species in that genus, antelope bitterbrush, rabbitbrush, mountain mahogany, and snakeweed. Pinyon-juniper persistent woodlands are dominated by trees, with a variety of tree ages, often in areas with winter or bi-modal precipitation. Persistent woodland sites are usually unproductive, with thin soils and sparse ground or shrub cover, often occurring on rocky or rugged terrain.

Pinyon juniper persistent woodland
Pinyon juniper savannah
Pinyon juniper shrubland

Biome classification

Pinyon–juniper plant community has been associated with desert climates, informally. Biome classification recognizes that pinyons require twelve inches of precipitation annually.[5] Small junipers may grow in climates down to nine inches precipitation annually. Because deserts are recognized to have less than ten inches of precipitation, and are generally barren of vegetation,[6] a pinyon tree cannot survive in the desert. Where climate exceeds ten inches annual precipitation the classification "steppes" is used.[7] Pinyons and junipers will grow preferentially in steppes of shallow soils, whereas grassland may dominate deeper soils.

Range
Range of pinyon–juniper Woodlands in the Western United States

The pinyon–juniper woodland range spans from New Mexico, to the eastern Sierra Nevada, the Colorado Plateau, the Great Basin, and higher elevations of Mountain ranges of the Mojave Desert.[2] The woodland's range includes the Mogollon Rim in the south, to its northern extent in the Snake River Plain.[8]

Arizona and New Mexico
In Santa Fe, New Mexico

The pinyon–juniper woodland is one of the most prevalent types of coniferous woodland in northern Arizona and New Mexico.[9] In Arizona the great basin woodland species are Juniperus arizonica, Juniperus californica in western Arizona, Juniperus deppeana, Juniperus monosperma, Juniperus osteosperma, Juniperus scopulorum at higher elevations, Pinus monophylla var. fallax below the Colorado plateau, and Pinus edulis on the Colorado plateau.[10] In Arizona the great basin woodland includes many species of oaks: Quercus turbinella, Quercus gambelii at higher elevations, Quercus grisea, Quercus arizonica, and Quercus emoryi. [11] In Southern Arizona, Pinus discolor, Juniperus deppeana, and Pinus leiophylla make up the conifer woodland with many oak species.[12]

Utah and Canyonlands region

The pinyon–juniper plant community covers a large portion of Utah and the Canyonlands region.[13] singleleaf ash (Fraxinus anomala), and Utah serviceberry (Amelanchier utahensis) are codominants of pinyon pine and Utah juniper.[13] In this region, the community occurs on rocky soils or jointed bedrock.[13]

Mojave Desert

In the steppes adjoining the Mojave Desert, this vegetation type can be found in areas receiving 12–20 inches of annual precipitation, and between 4,500 and 8,000 feet.[14] Associates include bitterbrush (Purshia glandulosa), Apache plume(Fallugia paradoxa), desert sagebrush (Artemisia tridentata), green ephedra (Ephedra viridis), mountain mahoganies (Cercocarpus spp.), and buckwheats (Eriogonum spp.).[14] In the Mojave, pinyon–juniper woodlands are generally above the Joshua Tree woodlands vegetation type, and requires more annual precipitation.[14][15]

Sierra Nevada

In the eastern Sierra Nevada, the elevation range is 4,000-5,500 feet in the north, and 5,000 to 8,000 feet in the southern reaches of the range.[16] Pinyon–juniper woodland requires 12–20 inches of annual precipitation, so is generally located above the sagebrush scrub vegetation type, which can survive on an average of 7 inches per year.[16] It is located below the alpine zone.[16] There is often an understory dominated by sagebrush (Artemisia tridentata) and its associates.[16] Co-dominants include Jeffrey Pine (Pinus jeffreyi) and an understory of sagebrush scrub or rabbitbrush scrub (Ericameria spp.).[16]

Other information

Pinyon pines have a very slow growth pattern and can take almost a century to reach 12 meters in height, only begin to grow cones after 35 years, and perform seed masting every 5 to 7 years throughout their lifetime. This particular woodland habitat is not adapted to fire, where fuel loads are not large or significant enough to maintain a devastating fire, although many of the accessory plants are particularly vulnerable to wildfires which can be critical to the environment because these tree species strictly rely upon various nurse plants for assistance in new growth. Though prescribed fire has been applied to these regions in order to manage the land, clear the landscape for new recruitment, or used to feed livestock animals, a negative consequence of prescribed burns usually deplete seed banks within the community as well as open the space to annual grasses which are more often invasive and ideal fuel stock. Cheatgrass is one of those invasive species that continues to promote type conversion via more frequent wildfire intervals. Variations in elevation create an ecotone between the juniper and pinyon species, where they can commonly overlap at around an elevation of 5,000 feet. However, there are some problems with the juniper species, specifically the Western juniper which can be invasive to the understory, herbaceous layer, and wildlife environments. Lack of an herbaceous layer leads to increased soil erosion and removal of groundwater resources due to the over exploitative nature that junipers have in that ecosystem.

See also
  • Category:Flora of the Southwestern United States
  • Category:Flora of the Great Basin
  • Category:Flora of the California desert regions

References
  1. "Pinyon-Juniper Woodland". Habitats Alive!. California Institute for Biodiversity. 6 September 2012. ISBN 978-0971125919.
  2. "Pinyon–Juniper Woodlands – Introduction & Distribution (U.S. National Park Service)". www.nps.gov. Retrieved 2018-01-26.
  3. Muldavin, Esteban; Triepke, F. Jack (1 July 2019). "North American Pinyon–Juniper Woodlands: Ecological Composition, Dynamics, and Future Trends" (PDF). North American Pinyon' Juniper Woodlands: Ecological Composition, Dynamics, and Future Trends. pp. 516–531. doi:10.1016/B978-0-12-409548-9.12113-X. ISBN 9780128160978. S2CID 213465284. Retrieved 5 February 2022.
  4. "Pinyon–juniper ecosystem". Digital-Desert: Mojave Desert. Retrieved 1 February 2016.
  5. "Singleleaf Pinyon Pinus monophylla Torr. & Frem" (PDF). USDA/NRCS Plant Materials Center. Retrieved 5 February 2022.
  6. "[Science Daily Reference Terms, Desert]". Science Daily. Retrieved 21 March 2019.
  7. "[The Grassland Biome]". Biomes Home UCMP authors. Retrieved 21 March 2019.
  8. Cronquist, (1972).
  9. Dick-Peddie, (1999) pp. 87.
  10. "Pinus monophylla (Singleleaf piñon) description - the Gymnosperm Database".
  11. "SEINet Portal NetworkResearch Checklist: Sedona/Oak Creek Canyon".
  12. "SEINet Portal NetworkResearch Checklist: Chiricahua National Monument".
  13. Damian Fagan, Canyon Country Wildflowers, p. 3
  14. Pam MacKay, Mojave Desert Wildflowers, p19-20
  15. Adrienne Knute, Plants of the East Mojave, p31.
  16. Karen Wiese, Sierra Nevada Wildflowers, 2013, p. 18

Sources
  • Dick-Peddie, William A. (1999). New Mexico Vegetation: Past, Present, and Future. University of New Mexico Press. p. 280. ISBN 0-8263-2164-X.
  • Cronquist, Arthur; Arthur H. Holmgren; Noel H. Holmgren; James L. Reveal; James Reveal; Noel Holmgren (1972). Intermountain Flora - Vascular Plants of the Intermountain West, U.S.A. - Geological and Botanical History of the Region, its Plant Geography and a Glossary. Vol. 1. The New York Botanical Garden Press. p. 270. ISBN 0-89327-300-7.
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