Effects of Restoration of Ponderosa Pine on Soil Chemical and Biological Properties in Northern Arizona.

Ecological restoration of ponderosa pine (Pinus ponderosa Dougl ex Laws) forest ecosystems to pre-settlement conditions in northern Arizona will have direct and indirect effects on soil chemical, physical, and biological properties.  The pre-settlement ponderosa pine ecosystem had widely spaced, uneven-aged pine stands with diverse native plant understories.  The human exclusion of wildfires and overgrazing by livestock since settlement have caused dramatic changes in this forest ecosystem that includes significantly increased numbers of tree stems, reduced understory cover and diversity, and the unintentional introduction of invasive, non-native understory species.  Ecological restoration treatments used in this ecosystem include tree stand thinning, prescribed burning, and changes in grazing practices.  This study reports on changes in select soil properties, including organic matter and soil respiration, twelve years after tree thinning and grazing exclosure treatments were applied in ponderosa pine forests, on three different soil/geologic parent material types near Flagstaff, Arizona.  Preliminary results are presented.