Preliminary results from the mineral ecosystem management area (EMA) experimental block study: One-year post-treatment. Special report to the Apache-Sitgreaves National Forests, USDA Forest Service, Region 3.

Southwestern ponderosa pine (Pinus ponderosa) forest ecosystems have become uncharacteristically dense as a result of livestock grazing, logging, and fire exclusion, which has led to an increase in vulnerability to high-severity, landscape-scale crown fires. In 2002, the Ecological Restoration Institute (ERI) at Northern Arizona University (NAU) and the Apache-Sitgreaves (A-S) National Forests cooperatively implemented a replicated ecological restoration experiment to (1) determine site-specific reference conditions, (2) measure and evaluate contemporary (pre-treatment) forest structure variables, and (3) test responses to three treatments: control, full restoration, and burn only. The site is located in a ponderosa pine forest and spans an elevation gradient from the pinyon-juniper ecotone to the dry mixed conifer ecotone. Reconstructed total basal area (BA) averaged 40 ft²/acre and total tree density averaged 35 trees/acre across all treatments indicating that a relatively open forest structure existed at the Mineral site in 1880. By 2002, prior to treatment, total BA had increased by more than 300% to an average of 125 ft²/acre and total tree density increased by more than 1000% to an average of 376 trees/acre. In 2009, following treatment, the full restoration treatment reduced total BA by 53% from 135 ft²/acre to 64 ft²/acre and total tree density by 83% from 404 trees/acre to 67 trees/acre. In the burn only treatment, total BA increased by 3% from 120 ft²/acre to 123 ft²/acre and tree density was reduced by 18% from 339 trees/acre to 279 trees/acre between 2002 and 2009. In the control, little change in total BA and tree density occurred between 2002 and 2009. Post-treatment diameter distributions in the full restoration treatment closely matched the historical distribution. In contrast, the burn only treatment had only small reductions in the lower diameter classes. Following treatment, about 15% of the presettlement trees died or were cut in the full restoration treatment compared to 23% mortality of presettlement trees in the burn only treatment. Ten percent of presettlement trees died in the control during the same time without active treatment. One year after application, the full restoration treatment shifted forest structure and diameter distributions within the range of variability historically present at the Mineral site. In contrast, the burn only treatment did not shift forest structure and diameter distributions within the historical range of variability in the short term. The ERI will conduct a five-year remeasurement at the Mineral site in the summer of 2013 and will build upon the information provided in this report to evaluate five-year post-treatment responses on forest structure, regeneration, surface fuels, canopy cover, herbaceous understory, and potential fire behavior