The effects of climate change, including warming temperatures and increasing droughts, are already evident in pinyon-juniper woodlands across the American Southwest.
Climate Change and Drought
The Intergovernmental Panel on Climate Change (IPPC) reports with “very high confidence” that terrestrial biological systems on all continents are now being affected by temperature increases, resulting in earlier spring events, shifts in the ranges of plant and animal species, and longer thermal growing seasons, among other impacts (IPPC 2007). Warming temperatures and increases in severe drought events in some regions are likely to lead to increased tree mortality and forest dieback, which in turn affect other disturbance processes, such as fire, erosion, and insect outbreaks (Allen 2007).
These effects have been observed over the past decade in pinyon-juniper woodlands across the American Southwest. Millions of hectares of woodlands in the southwestern United States have been altered by severe drought conditions since the late 1990s (Allen 2007). Extreme heat and lack of moisture have resulted in widespread mortality of many species of grasses, shrubs, trees, and cacti. During 2002 and 2003, greater than 95% mortality of non-seedling pinyon pine trees was observed in study plots at Bandelier National Monument in northern New Mexico (Allen 2007).
On a landscape level, pinyon pines weakened by drought stress have become an easy target for mortality-causing insects like the pinyon Ips bark beetle (Ips confusus). Endemic bark beetle populations can increase dramatically when moisture-stress weakens large numbers of trees, over large areas. Without adequate precipitation or snowmelt, trees are not able to repel attacking bark beetles with increased flows of pitch. Once insect populations are large enough, they are able to successfully attack healthy trees, as well as those affected by drought.
The severe drought conditions of the past decade have also set the stage for wildfires like the aforementioned large-scale stand-replacing fires in Mesa Verde National Park, where old growth pinyon-juniper woodland is being replaced by post-fire shrubland (Floyd et al. 2004). Drought and warming temperatures can increase the flammability of live and dead forest fuels, cause snowmelt to happen earlier in the spring, and lengthen fire seasons (Westerling et al. 2006).
Projections from multiple climate models predict that surface temperatures in the American Southwest will continue to rise, and that annual precipitation in this region is likely to decrease (Christensen et al. 2007). Less is known about how regional precipitation patterns may be affected in the future by climate change-driven fluctuations in sea surface temperatures and atmospheric circulation patterns (Miller 2005).
Allen, C. D. 2007. Interactions across spatial scales among forest dieback, fire, and erosion in northern New Mexico landscapes. Ecosystems 10:797-808.
Allen, C. D., and D. D. Breshears. 1998. Drought-induced shift of a forest-woodland ecotone: Rapid landscape response to climate variation. Proceedings of the National Academy of Sciences of the United States of America. 95(25):14839-14842.
Baker, W. L., and D. J. Shinneman. 2004. Fire and restoration of piñon-juniper woodlands in the western United States: a review. Forest Ecology and Management 189:1- 21.
Barth, R. C. 1980. Influence of Pinyon Pine Trees on Soil Chemical and Physical Properties. Soil Science Society of America Journal 44:112-114.
Belnap, J., and D. Eldridge. 2001. Disturbance and Recovery of Biological Soil Crusts. Pages 363-383 in Belnap, J., and O. L. Lange, editors. Biological Soil Crusts: Structure, Function, and Management. Ecological Studies, Vol. 150. Springer-Verlag Berlin Heidelberg New York. 503 pp.
Betancourt, J. L., E. A. Pierson, K. A. Rylander, J. A. Fairchild- Parks, and J. S. Dean. 1993. Influence of history and climate on New Mexico pinyon-juniper woodlands. Pages 42-62 in E. F. Aldon and D. W. Shaw, editors. Managing P-J Ecosystems for Sustainabililty and Social Needs: Symposium Proceedings. General Technical Report RM-236, USDA Forest Service, Rocky Mountain and Range Experiment Station.
Breshears, D. D., N. S. Cobb, P. M. Rich, K. P. Price, C. D. Allen, R. G. Balice, W. H. Romme, J. H. Kastens, M. L. Floyd, J. Belnap, J. J. Anderson, O. B. Myers, and C. W. Meyer. 2005. Regional vegetation die-off in response to global-change-type drought. PNAS 102(42):15144-15148.
Cartledge, T. R. and J. G. Propper. 1993. Piñon-juniper ecosystems through time: Information and insights from the past. From Aldon, E. C. and D. W. Shaw (Tech. Coords.). Managing piñon-juniper ecosystems for sustainability and social needs. USDA Forest Service General Technical Report RM-236.
Christensen, J. H., B. Hewitson, A. Busuioc, A. Chen, X. Gao, I. Held, R. Jones, R. K. Kolli, W.-T. Kwon, R. Laprise, V. Magaña Rueda, L. Mearns, C. G. Menéndez, J. Räisänen, A. Rinke, A. Sarr and P. Whetton. 2007. Chapter 11, Regional Climate Projections. Pages 847- 940 in Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller, editors. Climate Change 2007: The Physical Science Basis. Contribution of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. URL: http:// www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1- chapter11.pdf. Accessed December 2008.
Davenport, D.W., D. D. Breshears, B. P. Wilcox, and C. D. Allen. 1998. Viewpoint: Sustainability of piñon-juniper ecosystems- a unifying perspective of soil erosion thresholds. Journal of Range Management 51:231-240.
Daubenmire, R. F. 1943. Vegetational zonation in the Rocky Mountains. Botanical Review 9(6):325-393.
Flint-Lacey, P. R. 2003. The Ancestral Puebloans and their piñon-juniper woodlands. Pages 309-319 in L. M. Floyd, D. D. Hanna, W. H. Romme, M. Colyer, editors. Ancient Piñon-Juniper Woodlands: A Natural History of Mesa Verde Country. University Press of Colorado. 389 pp.
Floyd, M. L., W. H. Romme, and D. D. Hanna. 2000. Fire history and vegetation pattern in Mesa Verde National Park, Colorado, USA. Ecological Applications 10(6):1666-1680.
Floyd, M. L., D. D. Hanna, and W. H. Romme. 2004. Historical and recent fire regimes in piñon-juniper woodlands on Mesa Verde, Colorado, USA. Forest Ecology and Management 198:269-289.
Gori, D., and J. Bate. 2007. Historical range of variation and state and transition modeling of historical and current landscape conditions for montane grassland for the southwestern U.S. Prepared for the USDA Forest Service, Southwestern Region by The Nature Conservancy, Tuscon, AZ. 21pp. URL: http://azconservation.org/projects/ southwest_forest_assessment. Accessed September 2008.
Gottfried, G. J., T. J. Swetnam, C. D. Allen, J. L. Betancourt, and A. L. Chung-MacCoubrey. 1995. Pinyon-juniper woodlands. Pages 95-132 in D. M. Finch and J. A. Tainter, editors. Ecology, diversity, and sustainability of the middle Rio Grande basin. General Technical Report RM-268. USDA Forest Service, Fort Collins, Colorado, USA.
IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II, and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Pachauri, R.K. and A. Reisinger, editors. IPCC, Geneva, Switzerland. 104 pp. URL: http:// www.ipcc.ch/ipccreports/ar4-syr.htm. Accessed: November 2008.
Johnsen, T. N. 1962. One-seed juniper invasion of Northern Arizona Grasslands. Ecological Monographs. The Ecological Society of America 32(3):187-207.
Litzinger, W. J. 2003. A personal perspective on the ethnobotany of old-growth piñon-juniper woodlands. Pages 287-293 in L. M. Floyd, D. D. Hanna, W. H. Romme, M. Colyer, editors. Ancient Piñon-Juniper Woodlands: A Natural History of Mesa Verde Country. University Press of Colorado. 389 pp.
Miller, M. E. 2005. The structure and functioning of dryland ecosystems- Conceptual models to inform long-term ecological monitoring: U. S. Geological Survey Scientific Investigations Report 2005-5197. 74 pp.
Pavek, D. S. 1994. Pinus cembroides. In Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. URL: https://www.fs.fed.us/database/ feis. Accessed: October 2008.
Romme, W. H., C. D. Allen, J .D. Bailey, W. L. Baker, B. T. Bestelmeyer, P. M. Brown, K. S. Eisenhart, L. Floyd-Hanna, D. W. Huffman, B. Jacobs, R. F. Miller, E. Muldavin, T. W. Swetnam, R. J. Tausch, P. J. Weisberg. 2008. Historical and modern disturbance regimes, stand structures, and landscape dynamics in piñon-juniper vegetation of the western U.S. Colorado Forest Restoration Institute, Colorado State University, Fort Collins, CO. 35 pp.
Ronco, F. P. Jr. 1990. Pinus edulis. Silvics of North America, Vol. 1: Conifers. USDA Forest Service Agricultural Handbook 654:327-337.
Shaw, J. D., B. E. Steed, and L. T. DeBlander. 2005. Forest Inventory and Analysis (FIA) Annual Inventory answers the question: what is happening to pinyon-juniper woodlands? Journal of Forestry 103(6):280-285.
Tirmenstein, D. 1999. Juniperus deppeana. In Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. URL: https://www.fs.fed.us/database/ feis. Accessed: October 2008.
Westerling, A. L., H. G. Hidalgo, D. R. Cayan, and T. W. Swetnam. 2006. Warming and earlier spring increase western U.S. forest wildfire activity. Science 313:940- 943.
Wilcox, B. P., D. D. Breshears, and C. D. Allen. 2003. Ecohydrology of a resource-conserving semiarid woodland: Effects of scale and disturbance. Ecological Monographs 73(2):223-239.
For Further Information
National Park Service Inventory & Monitoring Program, Southern Colorado Plateau Network.
USDA Forest Service Fire Effects Information System.
IPCC (Intergovernmental Panel on Climate Change).
Prepared by Jamie Nielsen, Southern Colorado Plateau Network Inventory and Monitoring Program, 2009.
Series: Pinyon-Juniper Woodlands
Last updated: August 14, 2017