Historic Range of Variability for Upland Vegetation in the Medicine Bow United States Department of Agriculture National Forest, Wyoming Forest Service Gregory K. Dillon Rocky Mountain Dennis H. Knight Research Station Carolyn B. Meyer General Technical Report RMRS-GTR-139 September 2005 Dillon, Gregory K.; Knight, Dennis H.; Meyer, Carolyn B. 2005. Historic range of variability for upland vegetation in the Medicine Bow National Forest, Wyoming. Gen. Tech. Rep. RMRS-GTR-139. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 85 p. Abstract An approach for synthesizing the results of ecological research pertinent to land management is the analysis of the historic range of variability (HRV) for key ecosystem variables that are affected by management activities. This report provides an HRV analysis for the upland vegetation of the Medicine Bow National Forest in southeastern Wyoming. The variables include live tree density, dead tree (snag) density, canopy cover, abundance of coarse woody debris, species diversity, fire return intervals, the abundance of various diseases, the proportion of the landscape in differ- ent land cover types, and the degree of patchiness in the landscape. The variables were examined at the stand and landscape scales, using information available in the literature and USFS databases. High-elevation landscapes were considered separately from low-elevation landscapes. Much of the report pertains to forests dominated by lodgepole pine, subalpine fir, and Engelmann spruce at high elevations, and by ponderosa pine and aspen at lower elevations. We defined the HRV reference period for the MBNF as approximately 1600 to 1860. Keywords: aspen, bark beetles, canopy gaps, coarse woody debris, comandra blister rust, dwarf mistletoe, Engelmann spruce, fire effects, disease in Rocky Mountain forests, forest fragmentation, insects in forests, inte- rior forest, landscape ecology, lodgepole pine, mistletoe, mountain pine beetle, ponderosa pine, roads, Rocky Mountain forests, snags, spruce beetle, subalpine fir, subalpine forests, timber harvesting effects, white pine blis- ter rust, wind in forests The Authors Gregory K. Dillon is a GIS specialist with the Forest Service at the Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. His current work is focused on predictive mapping of biophysical settings in the United States for the LANDFIRE project. Previously, he did a variety of forest ecology and spatial analysis work at the University of Wyoming and for the Forest Service in the Southern Appalachians and Pacific Northwest. He received a B.S. degree in geography from James Madison University, Harrisonburg, Virginia, in 1995, and an M.A. degree in geography from the University of Wyoming in 1998. Dennis H. Knight is professor emeritus in the Department of Botany at the University of Wyoming, Laramie, WY. He retired in 2001 after 35 years on the faculty, where he taught courses in ecology and forest management. Much of his research focused on the effects of natural and human-caused disturbances on Rocky Mountain coniferous for- ests. In 1999 he contracted with the Rocky Mountain Regional Office of the Forest Service to prepare historic range of variability analyses for the upland vegetation of the Medicine Bow, Bighorn, and Shoshone National Forests in Wyoming. He received a bachelors degree in biology from Augustana College, Sioux Falls, South Dakota in 1959, and the Ph.D. in plant ecology from the University of Wisconsin-Madison in 1964. Carolyn B. Meyer is on the faculty of the Department of Botany at the University of Wyoming, Laramie, WY. Much of her research focuses on the study of spatial and temporal variation of ecological phenomena. She received a B.S. degree in natural resources from Humboldt State University, California in 1983, an M.S. degree in wildlife biology from the University of Wyoming in 1985, and a Ph.D. in ecology from the University of Wyoming in 1999. Prior to joining the faculty at Wyoming, she held research and management positions with the U.S. Fish and Wildlife Service and the National Park Service. Cover photo: Wyoming-Colorado border south of Encampment, photo by Lane Eskew. You may order additional copies of this publication by sending your mailing information in label form through one of the following media. Please specify the publication title and series number. Fort Collins Service Center Telephone (970) 498-1392 FAX (970) 498-1396 E-mail [email protected] Web site http://www.fs.fed.us/rm Mailing address Publications Distribution Rocky Mountain Research Station 240 West Prospect Road Fort Collins, CO 80526 Executive Summary The challenges of sustainable land management have led to an increased emphasis on incorporating the results of science in the decision making process. One approach for accomplishing this objective is through the analysis of the historic range of variability (HRV) for key ecosystem variables that are affected by management activities. The rationale for HRV analyses is that the chances of sustainable forest management are greater if the variation in man- aged ecosystems includes the range of conditions that are expected at various scales in ecosystems relatively unin- fluenced by humans. This report provides an HRV analysis for the upland vegetation of the Medicine Bow National Forest (MBNF). By definition, HRV analyses require the identification of specific variables and an estimation of how those vari- ables fluctuated, at more than one scale, prior to the advent of resource extraction and management by European- Americans. A complete list of the variables that we examined is found in table 7. Examples include live tree densi- ty, dead tree (snag) density, canopy cover, abundance of coarse woody debris, species diversity, fire return intervals, the abundance of various diseases, the proportion of the landscape in different land cover types, and the degree of patchiness in the landscape. We examined variables at two scales—the stand and the landscape—and we separat- ed high-elevation landscapes from low-elevation landscapes. Much of the report pertains to forests dominated by lodgepole pine, Engelmann spruce, and subalpine fir at high elevations, and ponderosa pine and aspen at lower el- evations. Our analysis emphasizes forests rather than grasslands and shrublands because more historical informa- tion is available for the forests. Two significant challenges for HRV analyses are 1) selecting a “reference period” for comparison to present day con- ditions, and 2) making decisions with very little data about range of variability during the reference period. We de- fined the HRV reference period for the MBNF as approximately 1600 to 1850, as some data sets on fire history go back several centuries and the influence of European-Americans in the MBNF was minimal until about 1850. We also compared MBNF ecosystems to comparable ecosystems in natural areas relatively uninfluenced by manage- ment activities, such as Yellowstone National Park. When data were lacking, our approach was to make plausible though qualitative judgments about the conditions that must have existed in the reference period based on current knowledge about plant adaptations and ecosystem structure and function. This approach is an example of deduc- tive science. There will always be some uncertainty in such conclusions, but our conclusions were evaluated and supported by a panel of four anonymous peer reviewers. For each of our conclusions about whether a stand or land- scape variable is within the HRV or trending away from that norm in managed landscapes, and the Forest as a whole, we indicate if our confidence level is low, moderate or high. Our report describes how the forests of the MBNF have evolved with regular disturbances, and how the kinds and frequency of disturbances have changed in some areas due to modern management practices. Over half of the for- ested area has been harvested for timber since the late 1800s (high- and low-elevation landscapes combined), and approximately 75% of the forests have been subjected to both harvesting and burning since that time. With the information available, we have attempted to draw conclusions about whether or not certain ecosystem variables are now beyond their HRV for the period 1600-1850 or trending in that direction (table 7). To summarize, we believe there is evidence to suggest that the following forest variables are within the HRV at high-elevations: • Extensive, stand-replacing fires • Insect population sizes • Abundance of diseases (including dwarf mistletoe in many areas) • Density of trees in all size classes (though the mean density may have been lowered in some areas) • Tree and understory plant cover and diversity (number of species) • Root/shoot ratios • Forest floor depth • Proportion of the landscape in different cover types • Ratio of forest to non-forest land Similarly, the following forest variables appear to be within the HRV at lower elevations: • Aspen stand abundance and stand structure • Abundance of native insects and diseases • Understory plant species diversity (number of species) i In contrast, we believe the following ecosystem variables are either beyond their HRV now or could be in the future if current management practices continue: Within stands at high elevations affected by timber harvest • Tree cover probably is lower and the number and size of canopy gaps probably is higher in harvested stands than the range of means (see text) for these variables during the HRV period in unmanaged forests of com- parable age and site conditions (moderate confidence), due primarily to selective and shelterwood cuts but also due to fewer standing-dead trees. • Where timber harvesting has occurred on the MBNF, snag density and the amount of coarse woody debris is lower than the range of means for these variables during the HRV reference period for unmanaged stands of comparable age and site conditions (high confidence). Whole-tree yarding can accentuate this variation by concentrating coarse woody debris and slash at landings in a way that has not occurred previously.