Pinyon-Juniper Ecosystem
Pinyon-juniper ecosystems are distributed throughout the western United States and are broadly defined as including one species of pinyon pine (subsection cembroides) and/or one species of juniper (section Sabina). The majority of the pinyon-juniper type is found in regions subject to temperature extremes and limited moisture availability. Pinyon-juniper generally occurs between 4,500 to 7,500 feet in elevation, transitioning from grasslands or shrublands at lower elevations, and to ponderosa pine (Pinus ponderosa) or other montane forest associations at higher elevations. The pinyon and juniper type is widespread on the Colorado Plateau, occurring between 5,000 to 7,000 feet in elevation. Range, species composition, structure, and stand characteristics are influenced by moisture availability and precipitation patterns. Generally, juniper is more abundant than pinyon at lower elevations and on drier sites, whereas pinyon pine occurs at higher elevations.
Restoration Principles
Persistent woodlands, savannas, and wooded shrublands tend to have dissimilar restoration needs. For example, persistent woodlands are unlikely to show functional changes related to fire exclusion; however, stand structure as well as soils and plant communities may show signs of degradation due to overharvesting and intensive livestock grazing. Research suggests that leaving woody biomass from tree thinning in place and seeding with native species can improve understory conditions in degraded woodlands. In some cases, resistance of highly degraded sites may require repeated or more exhaustive treatments.
In savannas, systems that show increases in tree density due to exclusion of natural surface fire, thinning and prescribed burning are common restoration treatments. In addition, use of thinning slash to hold soils and protect seedlings can be an effective element in a savanna restoration treatment prescription.
It should be noted that expansion of pinyon and juniper trees into grassland and shrubland habitats as a result of fire exclusion and climate variability has been widely reported. Goals and techniques developed for grassland restoration are appropriate in these circumstances. Lastly, hazardous fuels reduction treatments are commonly implemented in pinyon-juniper woodlands occurring in the wildland-urban interface. More research is needed to identify treatment approaches that reduce fuels and crown fire potential while simultaneously incorporating important conservation objectives in these situations.
Distribution of pinyon and/or juniper dominated woodland/savanna in Nevada, Utah, Colorado, Arizona, and New Mexico (NPS):
Historical Conditions
Three main pinyon-juniper structural types have been identified based primarily on canopy structure, understory characteristics, and historical disturbance regimes. Types have been described as persistent pinyon-juniper woodlands, pinyon-juniper savannas, and wooded shrublands, and although this is a broad classification these general types represent much of the variability in pinyon-juniper vegetation across the western United States. Historical stand structures, disturbance regimes, and landscape dynamics are notably different among these three basic types. Persistent pinyon‐juniper woodlands are found throughout the West, especially on low-productivity sites, where topography and fuels characteristics limit spread of surface fire, and where annual precipitation regimes support woody vegetation over herbaceous understories.
Fire Regime
Persistent woodlands, found commonly across the Colorado Pleateau, are characterized by infrequent high-severity fire occurring at various scales. Research indicates that successional processes and recovery of woodland conditions after stand-replacing fire may span more than a century. It is thought
that natural fire regimes of persistent woodlands have been only minimally affected by anthropogenic activities such as livestock grazing and fire suppression. Pinyon-juniper savannas are characterized as open communities of pinyon and/or juniper trees of varying ages, scattered across landscapes of abundant grasses and herbaceous plants. Savannas can be found where topography and climate allow contiguous occurrence of fine fuels and spread of surface fires. Historically, savanna communities were maintained by frequent fire, drought, and soil characteristics. Interruption of natural fire regimes in historical savannas has led to increases in tree cover and resulting shifts in ecosystem function. Pinyon-juniper savannas are found on some Colorado Plateau sites and in areas of the Southwest with strong summer monsoon climate.
Wooded shrublands are transitional communities of tree expansion and contraction. On sites where climate and soils conditions favor shrub success over occurrence of herbaceous communities, pinyon and juniper trees are found in varying densities and ages according to fire history. Fires in the wooded shrubland type are commonly high-severity. Wooded shrublands are found on the Colorado Plateau and in the Southwest, particularly on more arid sites that coincide with Interior chaparral and Madrean oak communities.
PJ Woodlands LEARN Sites
Mt Trumbull, AZ
Tusayan, Kaibab National Forest, AZ