Chapter 3 Pinyon-Juniper and Oak Woodlands Authors: Corrine Dolan and Alix Rogstad

Cover photo: Corva Prescribed Burn, July 2000. Courtesy of USDA Forest Service, Kaibab National Forest

Chapter 3 34 PINYON-JUNIPER AND OAK WOODLANDS

Description

Pinyon-juniper and oak (PJO) woodlands are found in the lower elevations that skirt the sky islands of southeastern Arizona and are widely distributed throughout the Colorado Plateau north and south of the Mogollon Rim (Figure 3.1). The PJO vegetation community is scattered in a wide belt between ponderosa pine forests and grasslands.

There are approximately 15 million acres of pinyon- juniper and oak woodlands combined in Arizona, the vast majority of which are pinyon-juniper woodland (USGS 2004). PJO occurs from 4,000 to 6,500 feet. PJO woodlands receive between 10 and 24 inches of annual precipitation, making these woodlands drier than the ponderosa pine forests that border their upper elevations.

Photo by Guy McPherson Some of Arizona’s fastest-growing residential communities are located in PJO woodlands. These Pinyon-juniper stand include towns such as Sierra Vista, Patagonia, Sonoita (Bahre 1991), Sedona, and Prescott. PJO woodlands are valued by humans for a variety of other reasons as well, including livestock grazing, Fire regime information is limited for PJO hiking, camping, hunting, watershed protection, woodlands because this vegetation community has and habitat for threatened and endangered wildlife been studied less than ponderosa pine or mixed (Kruse et al. 1996). conifer forests. The most current information suggests that wildland fires in PJO woodlands occurred with more variability than the neighboring ponderosa pine forests because the PJO woodlands are themselves more variable. For example, as opposed to ponderosa pine forests that have only two major overstory species, PJO woodlands have many different species of pinyon, juniper, and oak trees that make up the overstory. In addition, PJO woodlands have a wider distribution than the ponderosa pine forests in Arizona. Distribution of PJO woodlands can vary by soil type, topography, and geography. Plant species and variability woodlands and individual plant distribution create a more variable fire regime in PJO woodlands than in the forest communities described in this Photo by Guy McPherson publication. Boundary between oak woodland and grassland

Chapter 3 35 Pinyon-Juniper and Oak Woodland in Arizona

Figure 3.1 Pinyon-Juniper and Oak Woodlands in Arizona

Chapter 3 36 Associated Species

The most common species associated with pinyon-juniper and oak woodlands are listed below. Detailed PLANT FACT SHEETS with pictures of each species listed are located in Appendix C.

Box 3.1 Species Commonly Associated with Pinyon-Juniper and Oak Woodlands

Major Tree Species Understory Shrubs and Grasses Alligator juniper Rocky Mountain juniper (Juniperus deppeana) (Juniperus scopulorum) Big sagebrush (Artemisia tridentata)

Arizona white oak Shrub live oak (Quercus arizonica) (Quercus turbinella) Blue grama (Bouteloua gracilis)

Emory oak Single leaf pinyon (Quercus emoryi) (Pinus monophylla) Pinyon ricegrass (Piptochaetium fimbriatum)

Mexican blue Utah juniper (Quercus oblongifolia) (Juniperus osteosperma) Sideoats grama (Bouteloua curtipendula)

Pinyon pine Three awns (Pinus edulis) (Aristida spp.)

Chapter 3 37 Historic Fire Regime

Compared to ponderosa pine and mixed conifer forests, there is relatively little known about historic fire regimes in PJO woodlands, particularly in those areas dominated by evergreen oak species. Tree species in these woodlands, especially oaks, do not have fire scars or annual rings as distinct as other trees. This factor complicates the accurate reconstruction of fire history. Although subjective at this point, fire ecologists have been able to piece together some aspects of the historic fire regime in PJO woodlands.

Before major European-American settlement, pinyon-juniper and oak woodlands are thought to have had a mixed-severity fire regime. In other words, low, moderate and high-intensity, stand- Photo by Guy McPherson replacing fires occurred (Swetnam et al. 1992). Historic woodlands were open and grassy Fires may have burned for months at a time and burned thousands of acres (Swetnam 1988). On wetter sites, fine herbaceous fuels carried low- intensity fires while drier sites saw more stand- replacing fires carried by shrubby understories. The majority of these fires occurred in the summer (between May and late July) when thunderstorms Historically, pinyon-juniper and oak brought lightning ignitions. Historically, wildland woodlands developed with a mixed- fires are thought to have occurred every 5 to 40 severity fire regime. In other words, years on most sites dominated by PJO woodlands while others went a century or more without fire low, moderate, and high-intensity, (Zouhar 2001). The key point to remember is that stand-replacing fires all occurred at wildland fires in PJO woodlands occurred with more variability than in any of the other vegetation varying intervals. communities described in this publication.

Current Fire Regime

The current fire regime in PJO woodlands is vastly different from what is thought to have occurred Improper grazing management and full historically. Improper livestock grazing management and fire suppression have altered the naturally fire suppression have almost excluded complex PJO stands. Currently, stands are mostly wildfire in PJO woodlands. When uniform with respect to plant species, age, and wildfires do occur, they are usually size. Improper livestock grazing management in conjunction with full fire suppression management high-intensity and stand-replacing. strategies have decreased the amount of grasses that would naturally be present on a given site. As a consequence, the growth of woody species has

Chapter 3 38 been promoted. At present, the extremely dense natural mixed-severity regime that was present on woodlands are hard to ignite and do not carry fire the landscape before major European settlement as well without the grassy understory. This leads has all but disappeared (Allen 1996; Heyerdahl and to infrequent wildland fires occurring within this Alvarado 2003). vegetation community. Periods of dry and hot weather, however, can create conditions in which There are some special cases where fire might behave the abundant woody fuel does ignite. Once it does, differently or more unpredictably and are therefore the exceptionally crowded woodlands can produce of particular concern to fire managers. See Box 3.2 to a high-severity, stand-replacing wildland fire. The learn more.

Box 3.2 Special Cases SLOPE

Fire spreads more quickly on slopes than on flat terrain. A fire moving uphill preheats the fuels above it, moving the fire quickly up the slope. In addition, burning embers on slopes can roll down slopes and ignite fires in other areas.

RIDGE TOPS AND SOUTH FACING SLOPES

Oak woodlands on ridge tops and south-facing slopes are more open and have more grass in the understory and in openings than those found on slopes facing other direc- tions. Not only are these areas subject to rapid fire spread due to the slope, but there is also more fine fuel available to burn and carry the fire on south-facing slopes.

RIPARIAN AREAS

Riparian areas in PJO include more broad leaf tree species and different understory shrubs than the surrounding woodland. Riparian areas typically have denser vegeta- tion that, during dry years when fuel moistures are low, could increase fire intensities. On the other hand, during wet periods, riparian areas retain more moisture than upland areas and act as fuelbreaks when fire moves through an area.

Photos by Guy McPherson

Chapter 3 39 Fire Effects

establishment is generally delayed (sometimes 20-30 years) until a shrub layer becomes reestablished (Minnich 1999). Consequently, juniper species will dominate over pinyon species on a recently burned site.

Photo by Steven J. Baskauf

Mature Utah Juniper (Juniperus osteosperma)

Plants

Mature pinyon trees (Pinus spp.) are susceptible to College of California Photo courtesy of Saint Mary’s fire because they are short with large amounts of Young Pinyon Pine (Pinus edulis) foliage and do not self-prune their dead branches. Most, however, can survive low-intensity surface fires. Juniper trees Juniperus( spp.) are also susceptible to surface fires, but less so than pinyon species. Both pinyon and juniper trees over four feet tall are more fire resistant than shorter trees because the foliage is higher and the bark tends to be thicker (Scher 2002). Smaller trees are more vulnerable and can be killed by even low-intensity fires. Low-severity fires in mature pinyon-juniper stands will usually remove trees in the understory and a few overstory trees, while moderate-severity fires remove more of the overstory (Zouhar 2001). Alligator juniper (Juniperus deppeana) is the exception because it has the ability to resprout and can come back rapidly after a fire.

Pinyon trees reestablish on a burned site by Photo by Cori Dolan seed. Seedlings require nurse plants (primarily Gambel Oak leaves (Quercus gambelii) sagebrush) for establishment. Therefore, seedling

Chapter 3 40 The aboveground portion of oak trees (Quercus spp.) is usually killed by fire, but that does not necessarily mean the whole tree dies. Oak trees can resprout vigorously from the stump (Pavek 1993). Large trees can survive fires of low severity, although the acorns are frequently killed unless covered by a layer of soil (Bock and Bock 1990; Pavek 1994). Wildlife Native wildlife species in PJO woodlands have evolved with periodic fire at given, but variable, intervals. They have adaptations that allow them to survive the passage of fires of differing severities.

Courtesy of the U.S. Fish and Wildlife Service Generally, fire can produce positive effects Desert bighorn sheep (Ovis canadensis nelsoni) on wildlife populations and wildlife habitat. Short–term effects can include direct mortality of is rejuvenated by fires so much so that scientists individuals and loss of habitat. Although these are recommend allowing fires to burn in sheep habitat considered negative consequences, direct mortality (Krausman et al. 1994). In addition, white-tailed of animals due to fire is generally low and habitat deer (Odocoileus virginianus) thrive on areas loss is usually temporary. The long-term effects that have been recently burned due to the patchy include healthier wildlife populations due to habitat mosaic of habitat created by most fires and are seen regeneration. For example, desert bighorn sheep foraging on burned sites more frequently than on (Ovis canadensis nelsoni), thrive on habitat that adjacent unburned sites (Snyder 1991).

Human Dimension

One of the main factors affecting fire regime change in PJO woodlands is human activity on the landscape. The way people move on the landscape, utilize the woodlands, and alter the composition all affect the fire regimes in this vegetation community. Development Human presence and movement on the landscape has an impact on fire regimes in PJO woodlands. For example, the dramatic increase in Arizona’s population has led to an increase in the amount of development. In addition to the growth in Arizona’s metropolitan areas, the number of people moving into rural areas is also on the rise (Appendix A). In fact, PJO woodlands are among the fastest growing areas with regard to expanding residential communities, especially in towns such as Sierra Vista, Patagonia, and Sonoita (Bahre 1991) in southern Arizona and Flagstaff and Prescott in northern areas of the state. In addition, PJO woodlands are used heavily for hiking, camping, hunting, and other recreational activities.

Photo courtesy of the Bureau Land Management The landscape, as a result, is fragmented with Construction of a fuel break in the wildland-urban interface. expanding communities, structures, businesses,

Chapter 3 41 the materials that carried fire through a stand. Fragmentation of the landscape Full fire suppression management strategies also due to development of expanding decreased fire occurrence that was necessary for the herbaceous species to regenerate. Without an communities, structures, businesses, understory layer of fine fuels to carry fire, woody roads, and trails is one of the main species have become very dense and are hard to ignite. This leads to very infrequent wildland fires factors affecting the change in natural occurring in this vegetation community. Years fire regimes. with dry, hot, windy weather, however, can create conditions where the abundant woody fuel does ignite and supports fire spread. Once it does, the roads, and trails. Fragmentation disrupts natural exceptionally crowded woodlands typically produce fire regimes by changing the continuity and a high-severity, stand-replacing wildland fire. The distribution of fuels, and removing natural corridors natural mixed-severity regime that was present on for burning fires. the landscape before major human settlement has all but disappeared (Allen 1996; Heyerdahl and Livestock Grazing and Fire Suppression Alvarado 2003). The combination of improper livestock management Due to the decrease in key herbaceous forage and full fire suppression strategies has contributed species in some areas of Arizona, PJO woodlands to a decrease in fire frequency in PJO woodlands. are not currently used for livestock grazing as The result of these activities is the alteration of extensively as they have been historically. naturally complex PJO woodlands to stands that are homogenous with respect to plant species, Nonnative Plants age, and size. Improper livestock management Another alteration to vegetation communities is has led to a decrease in the amount of grasses the introduction of nonnative species. A nonnative present in the understory, thereby decreasing species is one that is introduced into a place outside of its natural range. Nonnative species can be introduced accidentally or intentionally. Most Box 3.3 Common Nonnative Plants in PJO nonnative species can become invasive and severely Woodlands alter the habitat that they are introduced into and are a major concern to land managers. Specifically, nonnative species can affect which plant species become established, how vegetation develops, Cheatgrass and can alter the fire regime by changing the fuel (Bromus tectorum) characteristics at a given site. Some of the more common nonnative species that affect fire regimes in PJO woodlands are listed in Box 3.3. Weeping & Lehmann’s In addition, some native species have become lovegrass invasive in this vegetation community. Improper livestock grazing management removed much of (Eragrostis spp.) the grassy understory, leaving it open for invasion by species that are native, but not normally there in such abundance, such as catclaw (Acacia greggii), Yellow and Malta wait-a-bit (Mimosa aculeaticarpa), pricklypear (Opuntia spp.), yucca (Yucca spp.), oak brush starthistle (Quercus spp.), and juniper (Juniperus spp.). (Centaurea spp.) These species do not carry fire as well as a stand of perennial grass, therefore fire occurrence is further reduced from its natural frequency.

Photo credits from top to bottom: Tom Huette, U.S. Forest Service; U.S. Fish and Wildlife Service; Apache-Sitgreaves National Forests

Chapter 3 42 Fire Management Techniques

The potential for crown fire in junipers is entirely limited to fire behavior driven by high winds in extremely dense continuous stands. During the Rodeo-Chediski Fire of 2002, the only juniper stands that burned were in the transition zone between ponderosa pine forest and juniper. In all cases where the fire burned into pure juniper stands it went to the ground and the lack of fine surface fuels prevented further spread (Steve Campbell, pers. comm.). Fire can be used as a tool to reduce the amount of some woody species in PJO. The desired condition

Photo by Guy McPherson Dense oak woodland for PJO is open woodlands with grassy breaks in vegetation. Fire can be used to decrease stand Pinyon-juniper and oak woodlands (PJO) are density by preventing establishment of new two difficult vegetation communities for fire seedlings (Allen 1996). management personnel. It is not easy to mimic natural fire activity since the actual fire return interval is not known. Currently, surface fuels tend to be too light to support surface fires or low-intensity fires in most PJO areas in Arizona. The exception is in Navajo county where there are significant fine fuels present throughout the pinyon-juniper stands in or bordering the Apache- Sitgreaves National Forests.

Wildland fire use (WFU) and prescribed fires are not as effective in PJO as in other vegetation communities because of the lack of surface fuels. When weather, wind, and fuel moisture conditions

are favorable for carrying prescribed fire, flame Photo courtesy of Kaibab National Forest. lengths tend to be long, reaching into the crown. Highly flammable trees carry fire into the crown. Some areas, such as the Gila National Forest in New Mexico, are experimenting with prescribed fires in pinyon-juniper stands under these dry and windy conditions. Some species of juniper, such as Utah juniper (Juniperus osteosperma), have highly flammable shaggy bark that burns readily even when exposed to shorter flame lengths. This carries fire into the crowns or effectively girdles most junipers that are exposed to flame contact, regardless of the intensity of the fire. The most common and effective treatment of PJO woodlands is mechanical fuels reduction. Trees must be thinned and lower branches trimmed extensively to reduce the threat of crown flames, particularly in wildland-urban interface (WUI) areas. Lower branches that often contact the ground are very common among all of the shaggy bark junipers.

Chapter 3 43 Pinyon-Juniper and Oak Woodlands Literature Cited

Allen, L. 1996. Ecological Role of Fire in the Mexico. 1994 September 19-23; Tucson, AZ. Madrean Province. In: Ffolliott, P.; DeBano, General Technical Report RM-GTR-264. Fort L.; Baker, M., Jr.; Gottfried, G.; Solis-Garza, Collins, CO: U.S. Department of Agriculture, Gilberto; Edminster, C.; Neary, D.; Allen, L.; Forest Service, Rocky Mountain Forest and Hamre, R., technical coordinators. Effects Range Experiment Station. p. 245-250. of Fire on Madrean Province Ecosystems: A Symposium Proceedings. General Technical Kruse, W., G. Gottfried, D. Bennett, and H. Mata- Report RM-GTR-289, Fort Collins, CO: U.S. Manqueros. 1996. The Role of Fire in Madrean Department of Agriculture, Forest Service, Encinal Oak and Pinyon-Juniper Woodland Rocky Mountain Forest and Range Experiment Development. In: Ffolliott, P.; DeBano, L.; Station: p. 5-10. Baker, M., Jr.; Gottfried, G.; Solis-Garza, Gilberto; Edminster, C.; Neary, D.; Allen, L.; Bahre, C. 1991. A Legacy of Change: Historic Hamre, R., technical coordinators. Effects Human Impact on Vegetation in the Arizona of Fire on Madrean Province Ecosystems: A Borderlands. Tucson, AZ, The University of Symposium Proceedings. General Technical Arizona Press. 231 p. Report RM-GTR-289, Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Bock, C. and J. Bock. 1990. Effects of fire on Rocky Mountain Forest and Range Experiment wildlife in southwestern lowland habitats. Station: p. 99-106. In: Krammes, J., technical coordinator. Effects of fire management on Southwestern natural Minnich, R. 1999. Vegetation, fire regimes, and resources: Proceedings of the symposium; forest dynamics. In: Miller, P.; McBride, J., eds. 1988 November 15-17; Tucson, AZ. General Oxidant air pollution impacts in the montane Technical Report RM-191. Fort Collins, CO: forests of southern California: a case study U.S. Department of Agriculture, Forest Service, of the San Bernadino Mountains. Ecological Rocky Mountain Forest and Range Experiment Studies: Analysis and Synthesis. Vol. 134. New Station: p. 50-64. York: Springer-Verlag: p. 44-80.

Campbell, Steve. University of Arizona Pavek, D. 1993. Quercus oblongifolia. In: Fire Cooperative Extension, Navajo County. Effects Information System, [Online]. U.S. Personal communication with author. 5 Department of Agriculture, Forest Service, January 2006. Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Heyerdahl, E. and E. Alvarado. 2003. Influence of Available: http://www.fs.fed.us/database/feis. climate and land use on historical surface fires in pine-oak forests, Sierra Madre Occidental, Pavek, D. 1994. Quercus emoryi. In: Fire Effects Mexico. In: Veblen, T; Montenegro, G.; Baker, Information System, [Online]. W.; and Swetnam, T., eds. Fire and Climatic U.S. Department of Agriculture, Forest Service, Change in Temperate Ecosystems of the Rocky Mountain Research Station, Fire Sciences Western Americas. Ecological Studies: Analysis Laboratory (Producer). Available: http://www. and Synthesis. Vol. 160. New York: Springer- fs.fed.us/database/feis. Verlag: p. 196-217. Scher, J. 2002. Juniperus scopulorum. In: Fire Krausman, P., W. Shaw, R. Etchberger, and L. Effects Information System, [Online]. U.S. Harris. 1994. The Decline of Bighorn Sheep Department of Agriculture, Forest Service, in the Santa Catalina Mountains, Arizona. Rocky Mountain Research Station, Fire Sciences In: Ffolliot, P., A. Ortego-Rubio, G. Gottfried, Laboratory (Producer). Available: http://www. R. Hamre, and C. Edminster, technical fs.fed.us/database/feis. coordinators. Biodiversity and management of the Madrean Archipelago: the Sky Islands of Snyder, S. 1991. Odocoileus virginianus. In: Fire southwestern United States and northwestern Effects Information System, [Online]. U.S.

Chapter 3 44 Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www. fs.fed.us/database/feis.

Swetnam, T. 1988. Fire History and Climate in the Southwestern United States. In: Krammes, J., technical coordinator. Effects of Fire Management of Southwestern Natural Resources. A Symposium, 15-17 November 1988, Tucson, AZ. USDA-FS. RM-GTR-191. p. 6-17.

Swetnam, T., C. Baisan, A. Caprio, and P. Brown. 1992. Fire history in a Mexican oak-pine woodland and adjacent montane conifer gallery forest in southeastern Arizona. In: Ffolliott, P., G. Gottfried, D. Bennett, V. Hernandez, A. Ortega-Rubio, and R. Hamre, technical coordinators. Ecology and Management of Oak and Associated Woodlands: Perspectives in the Southwestern United States and Northern Mexico, April 27-30, 1992, Sierra Vista, Arizona. USDA Forest Service General Technical Report RM-218. p.165-173.

USGS National Gap Analysis Program. 2004. Provisional Digital Land Cover Map for the Southwestern United States. Version 1.0. RS/ GIS Laboratory, College of Natural Resources, Utah State University.

Zouhar, K. 2001. Pinus monophylla. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www. fs.fed.us/database/feis.

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