Different Restoration Thinning Treatments Affect Level of Soil Disturbance in Ponderosa Pine Forests of Northern Arizona, USA

Forest restoration in southwestern ponderosa pine forests often consists of tree thinning and prescribed fire. Understanding the effects of thinning treatments on soil integrity is important due to the potential negative effects on soil properties and plant composition and abundance. We investigated the effects of harvest severity levels (control, low, intermediate, high) and harvest systems (machine, hand, whole-tree) on soil profile disturbance, soil bulk density, and dead woody biomass. There were no significant differences in soil profile disturbance, soil bulk density, or dead woody biomass among harvest severity levels. The whole-tree harvest system produced significantly larger areas with high levels of soil profile disturbance and significantly smaller areas with no soil disturbance than either the machine- or handharvest systems. There were no significant differences in soil bulk density due to insufficient sampling design. Dead woody biomass was significantly lower in the whole-tree harvested areas than the hand- or machine-harvested areas. Dead woody biomass can play an important role in providing microsites for plant reestablishment following disturbance. Our results illustrate that the type of harvest system used in forest restoration treatments is an important factor that needs to be incorporated into forest restoration design to insure compatibility with overall restoration goals. Keywords: harvest severity, harvest system, soil disturbance, forest restoration, ponderosa pine, Pinus ponderosa