Ecological restoration of forest ecosystems is a high priority for the U.S. Forest Service, as noted by Forest Service Chief Tom Tidwell. Many of the areas targeted for restoration are within the dry ponderosa pine and mixed-conifer forests of the Colorado Front Range and the South Dakota Black Hills. In fact, Congress awarded the a Collaborative Forest Landscape Restoration (CFLR) project to the Arapaho-Roosevelt and Pike-San Isabel National Forests, where more than 800,000 acres of lower montane forests consisting of ponderosa pine and Douglas-fir were identified as a high restoration priority. Stakeholders in the Black Hills National Forest have also attempted to apply for the CFLR program.
Historical range of variability (HRV) information can serve as a model for sustainable ecosystem conditions, and be useful for guiding the development of restoration treatment prescriptions and evaluating the success of treatments to bring about more resilient forest ecosystems. Based on HRV studies from other regions, such as ponderosa pine forests in the Southwest, the desired structural conditions for these forests suggest that forest structure should include grouping of trees (rather than even spacing), multiple age/size cohorts of tree groups, clumpy arrangement within groups, and variable spacing between groups.
However, for ponderosa pine and mixed-conifer forests of the Colorado Front Range and South Dakota Black Hills, a review of existing publications and interviews with scientific experts--intended to identify quantitative metrics describing historical forest structure and fire history--indicated that there were too few localized data to develop specific, or even general, restoration prescriptions. Although these types of studies have been performed in these forest types in the Southwest, experts agreed that climatic and topographic influences that govern disturbance regimes and their subsequent forest structure differ substantially in the Colorado Front Range and the Black Hills, thus specific regional knowledge is needed to guide restoration treatments.
Metrics for developing restoration treatment prescriptions include:
Tree and stand variables, including species composition, tree densities, basal areas, and tree spatial arrangements (including sizes and distribution of tree clumps) for a suite of topographic conditions (elevation, slope, and aspect).
Fire regime variables, including fire occurrences under various historical climate conditions; fire frequency; fire seasonality; spatial patterning of past fires; and fire behavior based on reconstructed fire effects, as well as relationships with driving forces such as climate and the potential responses to ongoing and future climate change.
Knowledge of science-based historical conditions provides not only the guidance but also the justification for restoration efforts, especially the use of and need for prescribed fires.