Pinyon–juniper woodland, also spelled piñon–juniper woodland, is a vegetation type of Western United States higher elevation deserts, characterized by being an open forest dominated by low, bushy, evergreen junipers, pinyon pines, and their associates which vary from region to region. The woodland's crown height may vary from less than 10 meters up to 15 meters, depending on the site. It may consist of pure stands of pinyon pine, or pure stands of juniper.
Pinyon–juniper plant community has been associated with desert climates, informally. Biome classification recognizes that pinyons require twelve inches of precipitation annually. 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,a pinyon tree cannot survive in the desert. Where climate exceeds ten inches annual precipitation the classification "steppes" is used.. Pinyons and junipers will grow preferentially in steppes of shallow soils, whereas grassland may dominate deeper soils.
The pinyon–juniper plant community covers a large portion of Utah and the Canyonlands region. singleleaf ash, and Utah serviceberry are codominants of pinyon pine and Utah juniper in this region. in this region, the community occurs on rocky soils or jointed bedrock.
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. Associates include bitterbrush, Apache plume, desert sagebrush, green ephedra, mountain mahoganies, and buckwheats. In the Mojave, pinyon–juniper woodlands are generally above the Joshua Tree woodlands vegetation type, and requires more annual precipitation.
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. 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. It is located below the alpine zone. There is often an understory dominated by sagebrush and its associates. Co-dominants include Jeffrey Pine and an understory of sagebrush scrub or rabbitbrush scrub.
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.
