Historical and Modern Disturbance Regimes of Piñon-Juniper Vegetation in the Western U.S.

Romme, William; Allen, Craig; Bailey, John; Baker, William; Bestelmeyer, Brandon; Brown, Peter; Eisenhart, Karen; Floyd-Hanna, Lisa; Huffman, David; Jacobs, Brian; Miller, Richard; Muldavin, Esteban; Swetman, Thomas; Tausch, Robin; Weisberg, Peter

Piñon-juniper vegetation covers some 100 million acres in the western U.S., where it provides economic products, ecosystem services, biodiversity, and aesthetic beauty in some of the most scenic landscapes of North America. There are concerns, however, that the ecological dynamics of piñon-juniper woodlands have changed since Euro-American settlement, that trees are growing unnaturally dense, and that woodlands are encroaching into former grasslands and shrublands. Yet surprisingly little research has been conducted on historical conditions and ecological processes in piñon-juniper vegetation, and the research that does exist demonstrates that piñon-juniper structure, composition, and disturbance regimes were very diverse historically as well as today. Uncertainties about historical stand structures and disturbance regimes in piñon-juniper vegetation create a serious conundrum for land managers and policymakers who are charged with overseeing the semi-arid landscapes of the West. Calls for restoration of historical conditions (i.e., those that prevailed before the changes wrought by Euro-American settlers) are being heard with increasing frequency. However, if those historical conditions are poorly understood it is difficult or impossible to set realistic targets for restoration. In the absence of site-specific information about historical disturbance regimes and landscape dynamics, there is danger that well-meaning “restoration” efforts actually may move piñon-juniper ecosystems farther from their historical condition. The purpose of this report is to briefly summarize our current understanding of historical stand structures, disturbance regimes, and landscape dynamics in piñon-juniper vegetation throughout the western U.S. The authors gathered for a workshop in Boulder, CO, on August 22- 24, 2006, to develop the information presented here. All have conducted research in piñon-juniper vegetation, and together they have experience with a wide diversity of piñon-juniper ecosystems, from New Mexico and Colorado to Nevada and Oregon. Our summary of current knowledge is presented as a series of statements, each followed by our level of confidence in the statement and the geographical area to which it applies. High-confidence statements generally are supported by rigorous field studies; statements of moderate confidence are based on anecdotal evidence or logical deductions, but lack the rigorous studies necessary to confirm or refute the idea. We intentionally refrain from making any specific policy or management recommendations in this paper. Instead we provide the consensus among researchers of what we know (and don’t know) about the science of piñon-juniper vegetation. The authors encourage managers and practitioners to give us feedback on the utility and shortcomings of this summary. There is much that we do not know about piñon-juniper vegetation, and new syntheses of this kind will be needed in the future as new knowledge becomes available.

Historical and Modern Disturbance Regimes of Piñon-Juniper Vegetation in the Western U.S.

Collections