Habitat type classifications have been developed for all federal lands in the Pacific Northwest, and plant associations are the basis for identifying specific habitat types with some of the earliest in the central Oregon pumice region

being those of Dyrness and Youngberg (1966) and Volland (1963). Correlations between productivity, plant associations, and environmental variables have been documented (Zobel et al., 1976, Gholz, 1982 and Churchill et al., 2013). Use of plant associations allows for ready communication with a diverse array of potential users and PLX3397 extrapolation of results of studies, such as ours. We used a publicly available map based on documented plant associations to assign inventory plot locations to habitat types (Fig. 1). The map depicts a projected distribution of potential vegetation types (PVTs) generated from existing plant association group (PAG) maps and Random Forest Nearest Neighbor imputation modeling using vegetation plot data (including Forest Inventory and Analysis, USFS Current Vegetation Survey, and USFS Ecoplots) and geophysical variables describing climate, typography, soil, and spectral reflectance as inputs (Henderson et al., In prep.). These PVTs represent a level of vegetation classification developed by the ILAP (Integrated Landscape Assessment Project) team that uses expert opinion to assign plant associations (Federal Geographic Data Committee (FGDC), 2008)

to PVTs based on similarity in growth rate, disturbance regime, and response to management. We focus on three major groups of dry forest sites based upon habitat types: ponderosa pine, dry mixed PD0332991 cell line conifer, and moist mixed

conifer. Detailed information on the plant associations included in each of these groups is found in Hopkins, 1979a, Hopkins, 1979b and Volland, 1985, and Simpson (2007). Ponderosa pine sites are represented by three distinct PVTs: Ponderosa pine – Xeric (hereafter PIPO Xeric sites), Ponderosa pine – Dry (hereafter PIPO Dry sites), and Ponderosa pine – Lodgepole pine (hereafter PIPO-PICO sites). PIPO Xeric sites are found at the lower forest line and largely identified by plant associations Thiamet G dominated by an understory of big sagebrush (Artemisia tridentata) and a significant presence of western juniper (Juniperus occidentalis) in the tree layer (M. Simpson, USDA FS, personal communication). PIPO Dry sites are commonly characterized by understories dominated by bitterbrush (Purshia tridentata). PIPO-PICO sites are similar to the PIPO Dry sites but exhibit higher levels of soil moisture availability as indicated by higher cover of herbs, such as needlegrass (Stipa occidentalis), in the understory. Both dry and moist mixed-conifer sites are distinguished by increased abundance of white fir, which is absent or rare on ponderosa pine sites. The dry and moist mixed-conifer sites are distinguished from each other by the associated shrubs and herbs.