Science-based ponderosa pine forest restoration on the Colorado Front Range
A large number of forested acres are scheduled for treatment over the next decade in an effort to restore historical forest structure and function. Implementation of science-based restoration prescriptions will ensure that the treatments Forest Service scientists put on the ground show ecological validity. In addition, stakeholders who are concerned with tree harvesting and other management activities can have greater confidence in our actions. Forest silviculturists are currently utilizing some of the site-specific data collected and analyzed by Forest Service scientists in their prescription development on a restoration treatment located on the Arapaho-Roosevelt national forests and the Pike and San Isabel national forests.
Congress established the Collaborative Forest Landscape Restoration Program in 2009 to promote a collaborative, science-based ecosystem restoration of priority forest landscapes, which includes the ecological restoration in fire-adapted ecosystems across the United States. Based on studies from other regions with ponderosa pine forests, the desired structure conditions identified for ponderosa pine forests suggests forest structure should include the following: grouping of trees (rather than even spacing), multiple age/size cohorts of tree groups, clumpy arrangement within groups, and variable spacing between groups. Differences in historical fire frequency and productivity limit the transportability of historical forest structure data from one region to another when informing restoration prescriptions.
A review of existing publications and interviews with scientific experts for the Colorado Front Range intended to identify quantitative metrics describing historical spatial forest structure and fire history indicated that there were too few localized data to develop general restoration prescriptions. The goal of this study is to characterize a historical range of variability of forest structure using a spatially explicit plot-based approach across gradients of elevation and moisture. Research scientists have established over one hundred fifty 0.5-hectare [1-acre] plots in ponderosa pine/dry mixed conifer forests from the Wyoming border down to Colorado Springs, Colorado. In these plots, the scientists have stem-mapped all pre-settlement trees/remnants, collected fire scars, and quantified current forest structure. The scientists are processing tree cores and fire scar samples, which includes sanding and cross dating. Initial analysis on a few sites indicates that historically, ponderosa pine and dry mixed conifer forests on the Colorado Front Range were less dense than contemporary forests. In contrast to the homogeneity and continuity of current forest structure, the historical forest structure was heterogeneous with a mixture of openings, single trees, and groups of two to five trees growing together.