Tuesday, August 5, 2008: 9:00 AM
104 D, Midwest Airlines Center
Background/Question/Methods An assessment of the historic range of variability (HRV) of vegetation in a national forest can provide a guide to achieving sustainable management. If current conditions are beyond the HRV, the system may not be sustainable. Because the HRV decreases with increasing spatial scale, we estimated the HRV for variables at the stand and landscape-scale for three national forests in Wyoming. The historic period was defined as the 400-year period before European-Americans arrived. If the HRV is defined as the absolute range of variables over the historic period, changes in variability may be missed. Thus, we defined HRV as a more useful measure called the “range of means” averaged over 30- to 50-year periods. Tree ring, fire, and stand age databases from the national forests or nearby similar areas such as Yellowstone National Park were used to determine the HRV of disturbance regimes and associated stand/landscape structural characteristics. For some variables, such as coarse woody debris, simulation models were employed.
Results/Conclusions In high-elevation forests of spruce and fir, snag density, coarse woody debris, tree canopy cover, tree age in north facing slopes, fire extent, interior habitat, and late successional forest proportions on the landscape were estimated to be below the HRV whereas landscape patchiness was higher than the HRV. In low elevation forests of ponderosa pine and Douglas-fir, fire frequency, tree size and age were estimated to be below the HRV, whereas tree density, cover, forest floor thickness, white pine blister rust infestations, and proportion of the landscape in forest were estimated to be greater than the HRV. Fire suppression has had its largest effect on low, rather than high-elevation forests, and current timber harvest patterns do not mimic natural disturbance patterns. Additionally, management for widespread stands of fast-growing trees with pathogens in low abundance creates conditions beyond the HRV. As expected, the less harvested national forests had more variables within the HRV.
Results/Conclusions In high-elevation forests of spruce and fir, snag density, coarse woody debris, tree canopy cover, tree age in north facing slopes, fire extent, interior habitat, and late successional forest proportions on the landscape were estimated to be below the HRV whereas landscape patchiness was higher than the HRV. In low elevation forests of ponderosa pine and Douglas-fir, fire frequency, tree size and age were estimated to be below the HRV, whereas tree density, cover, forest floor thickness, white pine blister rust infestations, and proportion of the landscape in forest were estimated to be greater than the HRV. Fire suppression has had its largest effect on low, rather than high-elevation forests, and current timber harvest patterns do not mimic natural disturbance patterns. Additionally, management for widespread stands of fast-growing trees with pathogens in low abundance creates conditions beyond the HRV. As expected, the less harvested national forests had more variables within the HRV.
