Pinyon-juniper (Pinus spp.-Juniperus spp.) communities occupy areas in 10 states of the Great Basin (to 42°N), the Colorado Plateau, the Rocky Mountains, and the Sonoran and Chihuahuan Deserts. It extends southward to the states of Jalisco and Puebla in Mexico (to 18°N). Pinyon and juniper trees grow together and tolerate a broad range of environmental conditions that allows them to compete in a variety of plant communities. Estimates of pinyon-juniper area vary with definitions and range from 17 to 55 million ha (42 to 136 million a). Area estimates from satellite imagery are 22.5 million ha (55.6 million a). Most of these ecosystems occur on public lands administered by the Forest Service and Bureau of Land Management, but about 7.7 million ha (19 million a) are present on non-federal lands. Pinyon-juniper is generally bounded by the northern desert shrub, desert plains grassland, or shortgrass plains at the lower part of its elevation range and by montane forest at its upper limits.
Location and Distribution
Pinyon-juniper (Pinus spp.-Juniperus spp.) communities occupy areas in 10 states of the Great Basin (to 42°N), the Colorado Plateau, the Rocky Mountains, and the Sonoran and Chihuahuan Deserts (Figure 1). It extends southward to the states of Jalisco and Puebla in Mexico (to 18°N). Pinyon and juniper trees grow together and tolerate a broad range of environmental conditions that allows them to compete in a variety of plant communities. Estimates of pinyon-juniper area vary with definitions and range from 17 to 55 million ha (42 to 136 million a). Area estimates from satellite imagery are 22.5 million ha (55.6 million a). Most of these ecosystems occur on public lands administered by the Forest Service and Bureau of Land Management, but about 7.7 million ha (19 million a) are present on non-federal lands. Pinyon-juniper is generally bounded by the northern desert shrub, desert plains grassland, or shortgrass plains at the lower part of its elevation range and by montane forest at its upper limits.
Drought and frost during the growing season limits distribution of pinyon-juniper woodlands in the Great Basin to relatively narrow altitudinal belts on the sides of mountains (Figure 2). In western Utah the elevation of pinyon-juniper sites on granite average 1,926 m (6319 ft) while those on sandstone averaged 1,341 m (4400 ft). In southern Nevada pinyon-juniper woodland occupies elevations from approximately 1250 to 2600 m (4100-8530 ft). Pinyon and juniper woodlands are widespread on the Colorado Plateau between about 1200 to 1500 m (5000 to 7000 ft) in elevation. Pinyon pines have been found to be less tolerant of drought and early spring frosts than junipers, and usually dominate the middle elevations while junipers tend to dominate both the higher and lower elevations of the woodland belt.
There is a northwest-to-southeast gradient in the seasonality of precipitation in intermountain and southwestern pinyon-juniper. Winter–spring precipitation predominates in the northwest, notably in the Great Basin, shifting to a bimodal winter–summer pattern on the Colorado Plateau, and a summer monsoonal regime in the southeastern portion of the region, including southern Arizona and New Mexico. Across most of this area precipitation ranges from 30 to 40 cm (12-15 in). The frost-free period is 120 days in the north to 200 days or more in the south.
Rainfall in Great Basin pinyon-juniper communities is heavily influenced by the rain shadow effect of the Cascade and Sierra Nevada Mountains. In the southwestern pinyon-juniper communities winter precipitation is mainly the result of frontal activity associated with Pacific Ocean storms moving west to east. Summer rainfall, frequently as part of intense thunderstorms, is the result of the generally southeasterly circulation from the Gulf of Mexico and strong orographic lifting as the air moves over higher terrain. July and August are usually the wettest months. Temperatures in pinyon juniper communities are heavily influenced by elevation and can range from below -18 °C (0 ° F) to greater than 38 °C (100 °F).
Topography and Soils
Great Basin and Southwestern topography is extremely varied, with valleys and lowlands separated by mountain ranges. Pinyon-juniper occurs on a wide range of landforms, including rocky plateaus, mesas, foothill terraces, and lower mountain slopes. Soils are derived from a wide variety of parent materials including basalt, tuff, pumice, granite, limestone, sandstone, and shale. Aridity has limited development of soils to the Alfisol, Entisol, Intceptisol, Mollisol and Aridisol soil orders. Soil textures range from coarse, rocky gravels to compacted clays.
Current Plant Communities
Scientists have identified three pinyon-juniper vegetation types (persistent juniper woodlands, pinyon-juniper savannas, and wooded shrublands), based primarily on canopy structure, understory characteristics, and historical disturbance regimes. There is great diversity within each of these general types with respect to species composition and stand structure, but this classification represents much of the variability in pinyon-juniper vegetation across the western United States. Historical stand structures, disturbance regimes, and landscape dynamics were significantly different among these three basic types.
Persistent pinyon‐juniper woodlands are found throughout the West and especially on portions of the Colorado Plateau, where precipitation is bimodal with small peaks in winter and summer. Large expanses of the Colorado Plateau are characterized by ancient, persistent woodlands within spectacular canyon and plateau landscapes.
Canopy structure of persistent pinyon‐juniper woodlands varies from sparse stands of scattered small trees growing on poor substrates to relatively dense stands of large trees on relatively productive sites. The canopy can be dominated by pinyon or juniper or the two may co‐dominate. The understory is characterized by low total plant cover and bare ground or rock patches are common. Shrubs or forbs may dominate the understory with graminoids being less common. It is important to note that this class of pinyon-juniper does not represent twentieth century conversion of formerly non‐woodland vegetation types to woodland, but places where trees have been an important stand component for at least the past several hundred years. Persistent woodlands commonly occur on rugged upland sites with shallow, coarse‐textured soils with relatively sparse herbaceous cover even in the absence of heavy livestock grazing. However, they also occur in a variety of other settings, and their precise spatial distribution and bio‐climatic context have not been characterized.
Pinyon‐juniper savannas are prevalent in the basins and foothills of central and southern New Mexico and Arizona, where the precipitation pattern is dominated by the summer monsoon. Pinyon‐juniper savannas are relatively rare where precipitation has a stronger winter component, as in the southern Rocky Mountains, northern Colorado Plateau, and Great Basin. Pinyon‐juniper savannas typically are found on moderately deep, coarse to fine‐textured soils on gentle upland and transitional valley locations in regions where a large proportion of annual precipitation comes during the growing season.
A relatively continuous grass cover in the understory is a key feature of the pinyon-juniper savanna. Pinyon‐juniper savannas are characterized by a low to moderate density, and cover of shrubs is relatively unimportant in this type. Pinyon or juniper may dominate the canopy, or the two may co‐dominate. This type usually occurs as a savanna but in places the density of trees may be enough to represent open woodland rather than a savanna.
Wooded shrublands are prevalent in the Great Basin, where the precipitation pattern is winter‐dominated, although they are found throughout the West. This type is associated with a wide variety of substrates and topographic settings, from shallow rocky soils on mountain slopes to deep soils of inter‐montane valleys. A shrub stratum dominates this type and the tree component may range from very sparse to relatively dense. The tree component may be either pinyon or juniper or both. Herbaceous cover is variable, depending on local site conditions and history.
This type occurs on sites where competition from grasses and shrubs, drought, and periodic disturbance by fire, insects, and disease limit the development of mature trees or stands over time. Consequently they are often located near a persistent tree seed source. In this type the shrubs are the fundamental biotic community and tree density naturally fluctuates over time in response to climatic fluctuation and disturbance (notably by fire and insects). Thus, these are areas of potential expansion and contraction of woodland within a shrub‐dominated matrix.
Juniper species common in the intermountain and southwestern state are western juniper (Juniperus occidentalis), Utah juniper (J. osteosperma), single seeded juniper (J. monosperma), alligator juniper (J. deppeana), redberry juniper (J.eythrocarpa), and rocky mountain juniper (J. scopulorum). Except for western juniper, these species are commonly associated with single-leaf pinyon (Pinus monophylla) or two-needle pinyon (P. edulis).
Species composition and vegetation structure vary along a northwest‐to-southeast gradient. Western juniper is the major woodland tree species in extreme northwestern Nevada, northeastern California, and eastern Oregon, while single-leaf pinyon and Utah juniper dominate woodlands elsewhere in the Great Basin. Two-needle pinyon and Utah juniper are the dominant woodland species across most of the Colorado Plateau and southern Rocky Mountains west of the Continental Divide and two-needle pinyon and single seeded juniper characterize the summer monsoon regions of New Mexico, east central Arizona, and the southern Rockies east of the Continental Divide. Two other junipers also are common at higher elevations, rocky mountain juniper in much of the Colorado Plateau and southern Rockies, and alligator juniper in southern New Mexico and Arizona.
In the western and northern regions, where precipitation is winter‐dominated, the trees are typically associated with a major shrub component, notably big sagebrush (Artemisia tridentata) and other Artemisia spp., bitterbrush (Purshia tridentata), rabbitbrush (Chrysothamnus spp. and Ericameria spp.), and mountain mahogany (Cercocarpus spp.). Cool and warm season perennial tussock grasses also may be common associates, including Idaho fescue (Festuca idahensis), bluebunch wheatgrass (Pseudoroegneria spicata), needlegrass (Achnatherum spp.), Sandberg bluegrass (Poa secunda), and muttongrass (P. fendleriana). In eastern and southern regions, where the precipitation pattern is summer‐dominated, pinyon and/or juniper woodlands often support an understory of warm‐season grasses such as blue grama (Bouteloua gracilis), sideoats grama (B. curtipendula), hairy grama (B. hirsute), black grama (B. eriopoda), New Mexico muhly (Muhlenbergia pauciflora), and curlyleaf muhly (M. setifolia), and woodlands may occur as patches within a grassland matrix. A diverse and highly variable mix of montane shrubs and chaparral species, including Gamble oak (Quercus gambelii), wavyleaf oak (Q.pauciloba), and other oaks (Quercus spp.), mountain mahogany (Cercocarpus montanus), Utah serviceberry (Amelanchier utahensis), and bitterbrush is an important component of pinyon‐juniper vegetation at higher elevations, notably in the southern Rockies and Colorado Plateau.
Many animal species find refuge in pinyon-juniper woodlands, including mule deer (Odocoileus hemionus), elk (Cervus canadensis), desert cottontail (Sylvilagus audubonii), pinyon jays (Gymnorhinus cyanocephalus), and Clark’s nutcrackers (Nucifraga columbiana). Both pinyon nuts and juniper berries are important food sources for wildlife, and many wildlife species serve as seed dispersal agents for these trees.
The pinyon jay is specialized for feeding on pine seeds and prefers pinyon-juniper woodlands and ponderosa pine (P. ponderosa) forests. Each jay stores thousands of seeds each year, and can remember where most of them were hidden. Pinyon jays interact in a mutual relationship with the pinyon. Pinyon trees provide pinyon jays with food, nesting and roosting sites, and breeding stimuli. Pinyon jays influence seed dispersal, establishment, and genetic structure of pinyon populations.
Sage grouse (Centrocercus spp.) are dependent upon sagebrush (Artemisia spp.) shrub-steppe throughout their distribution in western North America (Figure 8). Loss, fragmentation and degradation of sagebrush-dominated ecosystems have resulted in habitat loss and a decline in sage grouse populations. Juniper invasion into these sagebrush ecosystems has degraded habitat for sage grouse and their reduction is part of habitat restoration programs. Management of sagebrush-dominated habitats is necessary if viable populations of sage grouse are to persist. Enhancement of habitats to benefit sage grouse will require management prescriptions and experiments to learn if treatments result in increased population size and/or distribution.
Ancient packrat middens suggest that pinyon and juniper were growing in southeastern Oregon and other intermountain areas during portions of the late Pleistocene but they may have been distributed further south and at lower elevations. The earliest evidence of western juniper is in northeastern California and eastern Oregon between 4000 and 7000 years ago. Approximately 5400 years ago a period of extreme drought ended and, according to pollen counts, juniper began to increase approximately 4500 years ago. Increasingly wetter conditions enabled juniper to expand down slope and into more xeric communities. Abundance of juniper pollen has gradually increased since A.D. 1500, fluctuating in the early 1800s and sharply increasing in the mid-1900s. Relict juniper woodlands, tree-age class ratios, fire scars and historical documents generally indicate that pinyon-juniper and juniper woodlands, before the Euro-American settlement, were open, sparse and savanna-like or confined to rocky ridges and rocky low sagebrush flats where fine fuels were too low in abundance to carry a fire. However, during the last 150 years, juniper species have increased in distribution and density throughout their range.
Pinyon-juniper vegetation has changed due to human activities associated with settlement of the West. Rapid expansion of the woodland during the late 1800s and early 1900s resulted from a combination of conditions including: (1) heavy livestock grazing that removed the herbaceous vegetation (fine fuels); (2) the associated reduction in the presence of fire; and, (3) wet conditions that created an ideal situation for tree establishment. Since European settlement of the West in the 1800s, trees have expanded into adjacent shrub and grassland communities and their dominance on the site has increased.
A great deal of the woodland expansion has been into the more productive sites such as canyon bottoms and swales. Without fire, the trees are well-adapted and competitive in these more productive locations. Prior to tree expansion these areas represented some of the more diverse and productive sagebrush ecosystems in the region. Following woodland expansion these sites support some of the highest levels of tree dominance and fuel loads. There has been up to a 10-fold increase in tree densities since settlement by Europeans. Lesser density increases may have occurred on the eastern Colorado Plateau. As the area of tree dominance increases the heterogeneous sagebrush dominated ecosystems of the Great Basin are being replaced by homogenous woodlands.
Before about 1870, woodlands occurred on less than 10% of their currently occupied area in the northwest Great Basin and on less than 30% in the central and southern Great Basin. Little information is available on the pre-settlement woodlands of the Colorado Plateau. Expansion woodlands now cover an average of three to four times the pre-Euro-American settlement area. This woodland expansion has proceeded at a nearly continuous rate across the Great Basin over the last 100 years and possibly equals or exceeds previous woodland expansions of the Holocene. Scientists believe that sagebrush communities will continue to decline as tree dominance continues to increase. On the Colorado Plateau, juniper has expanded downslope from rocky uplands and outward into grasslands.
The rate of the transition from sagebrush ecosystem to tree-dominated woodland is variable and depends on the site potential, sagebrush species and subspecies present, and rate of tree establishment. Because of the generally slow growth of the trees, it has taken all of the approximately 100 years since Euro- American settlement for a doubling of the fuel loads to take place. In general, a minimum of 60 to 90 years is required for trees to dominate a site.
Scientists have describe three phases of woodland development associated with western juniper encroachment into sagebrush and sagebrush-grass communities. Phase I is the initial period when shrubs and herbs dominate the community and ecosystem processes, and trees are present but not dominant. In Phase II trees, shrubs and herbs are co-dominants and all three vegetation layers influence ecosystem processes. In Phase III the trees dominated ecosystem process and shrub and herb cover are reduced, sometimes substantially. The state of woodland development influences plant community structure, composition, seed pools, habitat quality and ecological process such as hydrologic and nutrient cycles. The stage of woodland succession also affects the selection of management treatments, response following treatment, follow up management and treatment costs. While encroachment of other juniper or pinyon pine species into adjacent shrub ecosystems may not result in identical states or transitions to those in western juniper, this developmental sequence can be a guide to woodland development in other juniper and pinyon pine communities.
Pre-settlement fires were common in the pinyon-juniper woodlands of the Great Basin. However, after settlement the fire frequency decreased due to fire suppression and heavy grazing of fine fuels. These conditions facilitated increased density and crown cover of pinyon-juniper. With more recent buildup of ground fuels there has been a shift from more frequent, low-intensity, small fires, to less frequent, larger, high-intensity fires. Many believe that the Great Basin faces a future of increased probability of crown-fires, invasion by introduced annuals and short-lived perennials, and then repeated burning and permanent site degradation unless seeding of desirable understory species takes place.
Post-fire vegetation response depends on the composition of the shrub-dominated community and the level of tree dominance. As the trees dominate a site, there is a decrease in the herbaceous species, an increase in soil erosion, changes in soil fertility, losses in forage production, and changes in wildlife habitat. The more dominant the trees at the time of disturbance, the more the plant species composition of the communities that follow the disturbance can change. The intense crown fires, more frequently occurring on tree-dominated sites, further reduces understory plant species survival. Exotic species are changing the outcome of post-fire response. The higher the level of tree dominance, the higher the probability that a crown fire will leave an open site. These open sites are increasingly being dominated by exotic plant species, many of which are annuals, such as cheatgrass (Bromus tectorum).
The introduction of large numbers of domestic livestock and the aggressive suppression of fire has had a major impact in the character and range of these juniper and pinyon communities. This impact began in the southwest in the early 1600s following Spanish colonization, whereas it did not affect the Great Basin until the mid-1800s. Grazing reduced the herbaceous vegetation cover, which resulted in a reduction in fire frequency. The reduction of herbaceous species by grazing also promoted an increase in shrub cover. The shrubs acted a nurse crop and promoted tree seedling establishment. With the reduction in fire frequency, the new tree seedlings were able to survive and the areas of woodlands expanded. As with pre-settlement woodlands, total vegetation cover of expansion woodlands remains relatively similar to the shrub cover that preceded tree dominance. Therefore, when the shrub layer was absent, the establishment of the trees was more limited.
With increased density of trees the probability that a crown fire will leave an open site has increased. These open sites are increasingly being dominated by exotic plant species, many of which are annuals such as cheatgrass. The presence of cheatgrass can cause increases in fire size and frequency and homogeneity of those communities across the landscape. More recently, exotic perennials have begun establishing in these areas. Once this conversion occurs, any return to the original sagebrush ecosystem, or even eventually to woodland, is often no longer possible without extreme restoration efforts.
The problems associated with the exotic grasses are increasing through time in proportion to the level of CO2 in the atmosphere. Three ecotypes of cheatgrass from three elevations in the Great Basin have been investigated for the effects of increasing levels of atmospheric CO2. Four levels of CO2 were used, ranging from pre-settlement to an estimate of 2020 levels. From pre-industrial levels to the estimated 2020 level, the productivity of the upper elevation ecotype doubles, the mid-elevation increases 2.5 times, and the low-elevation triples. Flammability also increases. Cheatgrass will have an increasingly negative impact over time on any woodland site where it becomes established following fire.
Harvesting of trees in pinyon-juniper ecosystems provided energy for mining, industries, and domestic purposes in the late 19th century. Use of pinyon and juniper wood for home heating and cooking was widespread until use of fossil fuels became common after World War II. Large mining operations in Nevada and California quickly exhausted existing pinyon or juniper trees in the 1860s. The demand for charcoal was so great that deforestation became a severe problem. In Nevada, it is estimated that 1619 to 2024 ha (4,000 to 5,000 a) of woodland had to be cut annually to supply the Eureka District.
Many pinyon and juniper communities in the West have been subjected to intensive livestock grazing. Grazing impacts, along with recent changes in fire regimes and localized tree harvesting, has contributed to changes in tree presence, age structure, density, and particularly to the composition of understory species. Loss of habitat, diminished watershed conditions, and the recent increase of weeds have created serious management problems. In addition, increases in wildfire frequency caused by the presence of annual weeds, and increases in the frequency of devastating wildfires within overgrown stands of trees, are a more recent problem associated with disturbed woodland conditions. The decline and loss of understory species coupled with an increase in tree overstory ultimately results in a loss of species richness and likely conversion to a dominance of undesirable weeds. Recent appearance of more troublesome and persistent perennial weeds within pinyon and juniper communities creates additional need to retain native understory species.
Juniper and Pinyon Expansion
Since approximately 1860, the area and density of trees has increased from three- to ten-fold due to fire exclusion, over-grazing, favorable climate, and recovery from settlement-era harvesting. The expansion and infilling of pinyon and juniper trees increases the risk of larger and more severe wildfires and, at low to mid-elevations, cheatgrass invasion. Land managers across the region are using fire and fire surrogate treatments (e.g., cut and leave, mastication) in an attempt to both increase the ecological resilience of sagebrush ecosystems and decrease the risk of high-severity fires.
Exotic annual grasses, including medusahead (Taenatherum caput-medusa), red brome (Bromus rubens), and cheatgrass, are rapidly expanding throughout the Great Basin (Figure 9), and altering fire regimes in native communities by increasing fine fuels and the rate of fire spread (Link and others 2006). In many parts of the region, an annual grass-fire cycle now exists in which fire return intervals have decreased from about 60 to 110 years to as little as 3 to 5 years.
Agency scientists have developed a guide that can be used by agencies, private landowners and NGOs to manage pinyon-juniper. Goals for treating pinyon-juniper woodlands include fuel load reductions, restoration of sagebrush communities, increasing the heterogeneity of the landscape and associated disturbance processes, improving watershed protection, enhancing wildlife habitat, and increasing forage production.
The locations of the treatment sites or patches should be based on topographic features and areas that tend to have a higher fire frequency and were more likely dominated by sagebrush communities. These are areas with deeper soils and higher herbaceous vegetation productivity that can carry fire. Retaining pre-settlement woodland sites requires as much or more effort to restore the surrounding communities as it does to restore the pre-settlement site. Many treatment procedures have been attempted, but they have often been unsuccessful over the long term because of the lack of information about treatments. A focus on landscape scales, rather than on just individual project scales, can improve treatment effectiveness. Central to this has been the general lack of recognition of the variability of the communities that the trees are capable of dominating, and the range of disturbance histories represented by the previous communities.
Tree removal is the primary management option for restoring areas affected by the ongoing woodland expansion. However, additional treatments have been proposed, many of them using new techniques. First and second order effects, and the success and longevity of the outcomes of any treatment, are highly specific to the site and the method used, how the treatment is used and its timing.
Tree removal treatments should focus on Phase I and II of woodland development, especially on productive sites with deep soils. By Phase III woodland fuels have shifted from ground fuels to canopy fuels which will increase the chances of infrequent high intensity fires. Mechanical methods are often used in Phases II and III woodlands, however, they make seedbed preparation and sowing difficult when the site requires revegetation. Prescribed fire is useful in large landscapes when woodlands are in Phase I or II, especially when native perennials are abundant in the understory. Sites that are in late Phase II and III may have trouble carrying a fire because of limited ground cover and ladder fuels.
Prescribed fire may be used to remove trees and restore sagebrush communities before tree dominance is so high it reduces surface fuels to a low enough level that they cannot carry fire (Figure 13). Once tree dominance is at the high levels for an extended period of time, susceptibility to the establishment of exotics such as cheatgrass increases. Once these levels of dominance are reached, some form of mechanical treatment followed by seeding is necessary to reduce the level of tree dominance. This allows recovery of sagebrush and herbaceous vegetation before the use of prescribed fire can more fully restore a sagebrush ecosystem.
Prescribed fire in pinyon-juniper has been used to control the establishment of trees, increase forb productivity, increase habitat diversity, control invasion of other conifers, alter herbivore distribution, enhance forage palatability and nutritive quality, and prepare sites for reseeding. While prescribed fire can be beneficial, many limitations exist. Vegetation response following fire depends on the composition of the shrub community on a site and the level of tree dominance. As trees increasingly dominate a site, the associated sagebrush ecosystems are greatly reduced. This reduction in fine fuels often makes it difficult for a fire to carry through a mid-successional stand. If fire does occur, increasing tree dominance increases the recovery time of herbaceous plants and increases the potential for invasion of exotic plants and erosion.
Chaining and thinning are the most commonly used mechanical methods to reduce tree cover. This may be necessary prior to prescribed burning in order to reduce crown fuels and stimulate understory vegetation. In Spanish Fork Canyon, UT, chaining increased total ground cover from 47 to 80 percent and forage production from < 22 kg/ha (<20 lbs./acre) to 1,120 kg/ha (1,000 lbs./acre) 7 years after treatment. Similar increases were seen between 4 and 7 years after chaining in eastern Nevada this initial increase in ground cover resulted in significantly less runoff and soil erosion than the control area. The size, type, and arrangement of the chain can be varied to accomplish different objectives and control the size and amount of trees removed. Double chaining in opposite directions removes additional trees missed in the first pass and covers the seed after the area has been broadcast seeded prior to the second pass. A once-over chaining is appropriate if sufficient understory remains, trees are sparse and mature, and seeding is not required. Although usually a stand-alone procedure, chaining should generally be used only as an effective first treatment followed by a second treatment, such as prescribed fire, which would remove the surviving trees.
Thinning overstory trees with handsaws reduces tree cover and causes less soil disturbance than chaining. In a case study in New Mexico, it was reported that herbaceous cover two growing seasons after hand felling juniper trees without seeding was 2.5 times greater. With this method trees can marketed as a fuelwood sale to offset costs.
Mastication is another increasingly popular mechanical thinning method. This method grinds and chips trees to reduce tree cover and compact fuel beds. Over 13,360 ha (33,000 a) have been masticated in Utah alone (Bruce Roundy, personal communication). Mastication has been shown to increase infiltration and decrease sediment yields. Mastication is also used to create fire breaks in pinyon-juniper woodlands.
Herbicides to control encroaching pinyon and juniper trees are another alternative to reduce tree cover. Basal spraying of herbicides allows for highly selective application with little effect on non-target species but application of Tebuthiuron (Spike® 80W) and picloram (Tordon® 22K) is more common in pinyon-juniper communities. Researchers have found that control was best for trees less than 1.8 m (6 ft.) in height, with picloram killing over 90% of the sprouts and seedlings. Tebuthiuron, a slower acting herbicide, killed 30- 60% of the sprouts and seedlings after 9 months, but results were expected to improve over time. Mortality of trees taller than 1.8 m (6 ft.) was between 10% and 30% for picloram and 5% and 10% for tebuthiuron. Individual tree application is best suited for newly invaded sites with fewer than 500 trees/ha (200 trees/acre) under 1.8 m (6 ft.) tall. The longevity of these treatments will depend on the number and age class of the trees removed. Concentrating only on the older trees and leaving many of the younger trees will reduce the longevity of the treatment.
Seeding may be required to prevent the establishment of exotic weeds if the understory is depauperate. After a tree removal treatment, seeding should occur prior to the next growing season to restrict the establishment of exotics. Fall seeding is the most ideal time to seed in the Intermountain West, although in southern Utah, seeding just prior to mid-July monsoons has also been successful. Fixed wing aircraft, helicopters, or rangeland drills are normally used for seeding. Aerial seeding treats large areas on steeper slopes or where tree densities are high. Drill seeding is used in open areas. Aerial seeding followed by chaining after fire significantly increased seeded grass cover and decreased cheatgrass cover compared to seeding alone. Broadcast seeding is often the method of choice because tree stumps, downed trees and slash are present after mechanical treatments. In Phase I and low-density Phase II sites drill seeding or broadcast seeding following chaining are the preferred methods.
Historically, introduced species seed mixes were used to control soil erosion and increase forage production. In recent years, there has been more interest in using native seed mixes to increase species diversity and restore ecosystems. Successful establishment of native grasses and forbs from different seed mixes has been demonstrated in several recent studies.
Pinyon-juniper vegetation has long been important to local communities for such products as fuelwood, charcoal, fence posts, wood mulch, pine nuts, forage for livestock and watershed protection. More recently, communities and businesses have begun to turn to pinyon-juniper as a source of biomass for fuel and energy. However, harvest and transportation costs have limited development of this energy source. In Lassen County, California there is interest in developing a biomass plant so that juniper harvested in restoration projects can be converted to “green energy.” Recreation in these woodlands includes hunting, bird watching, and hiking and off-road vehicle activities.
The charcoal kilns complex in Wildrose Canyon in Death Valley National Park is among the more remarkable historical-architectural features in the park. These kilns were used to reduce pinyon pine and juniper trees to charcoal in a process of slow burning in low oxygen. These beehive shaped masonry structures, about 7.6 m (25 feet high), are believed to be the best known surviving example of such kilns to be found in the western states. The Wildrose Charcoal Kilns were completed in 1877 by the Modock Consolidated Mining Company to provide a source of fuel suitable for use in two smelters adjacent to their group of lead-silver mines in the Argus Range west of Panamint Valley, about 40 km (25 mi) distant from the kilns. George Hearst, father of William Randolph Hearst, was involved in the Modock Company.
About 80% of the pinyon -juniper type is grazed. Livestock carrying capacities range from 2-8 ha (4-19 a) per animal-unit-month of grazing. Much of the area is overgrazed, and in some areas livestock consume the tree growth. This vegetation type represents one of the more important deer habitats of the southwestern United States.