These maps are tied to the tree diagram for the 38 model variables, which drive the distribution of a species. The 38 variable are divided into five categories including Climate (7), Soil Properties (12), Soil Types (9), Elevation (5), and Landscape (5). Due to the nature of the non-climatic variables, the seven climate variables were only mapped for each scenario to compare the differences in the models. Within the Climate tab, two maps have been provided so that a comparison can be made by selecting two models. Maps are based on a 20 x 20km grid of cells that make up the extent of the United States east of the 100th Meridian. The scale is 1:33,000,000 and is projected in Clarke 1866 Albers.
Climate
The climate will be affected by the emission levels of each scenario, and the results of nine models have been included for each variable. The legend contains the temperature in degrees Celsius; the scale for the current climate differs slightly from the other scenarios which all have the same temperature scale.
Mean Annual Temperature (°C) - average annual temperature for the counties occupied by the species. Data from USEPA (1993).
Mean January Temperature (°C) - average January temperature for the counties occupied by the species. Data from USEPA (1993).
Mean July Temperature (°C) - average July temperature for the counties occupied by the species. Data from USEPA (1993).
Mean May-September Temperature (°C) -
Annual Precipitation (mm) - average annual precipitation for the counties occupied by the species. Data from USEPA (1993).
Mean May-September Precipitation (mm) -
Mean Difference between July and January Temperature (°C) -
Soil Properties
Soil Bulk Density (g/cm3) - the weight of soil (oven dry) per unit volume. It indicates the pore space available for water and roots and is influenced by texture, kind of clay, content of organic matter, and soil structure.
Soil PropertiesPercent Clay (< 0.002 mm size) - the percentage of clay in the soil column to a depth of 60 inches (152 cm) or the depth to bedrock. Data from STATSGO, and calculated as for pH.
Soil Erodibility Factor, rock fragment free (susceptibility of soil erosion to water movement) - the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The values range from 0.02 to 0.69.
Percent Soil Passing Sieve No. 10 (coarse) - the percentage of the soil fraction less than 3 inches in diameter based on an oven dry weight. Has an opening of 2.00 millimeters.
Percent Soil Passing Sieve No. 200 (fine) - the percentage of the soil fraction less than 3 inches in diameter based on an oven dry weight. Has an opening of 0.074 millimeters.
Organic Matter Content (% by weight) - the percentage of organic matter in the surface layer of the soil. Data from STATSGO, and calculated as for slope.
Potential Soil Productivity (m3 of timber/ha) - The capability of a soil for producing a specified plant or sequence of plants under specific management.
Soil Permeability Rate (cm/hr) - the property of the soil that permits transmission of water through the soil, and is related to hydraulic conductivity of the soil. The finer the material (less porous), the slower the permeability. Reported for the counties occupied by the species, the data are processed from STATSGO, as discussed above for pH.
Soil pH - average pH for soils in the counties occupied by the species. Data are from STATSGO (Soil Conservation Service 1991), and because tabular data are reported by layer and soil series, three weighted averages were needed to calculate a county average (Iverson et al. 1996). First, a weighted average, based on the thickness of each layer to a depth of 60 inches (152 cm) or the depth to bedrock, was calculated for each soil series. Then, area-weighted averages were calculated for map unit and county as described for slope.
Depth to bedrock (cm) - the depth of all soil horizons to the bedrock.
Soil slope (%) of a soil component - average percent slope for the counties occupied by the species. Data from the State Soil Geographic Data Base (STATSGO), developed by the US Natural Resource Conservation Service on 1:250,00 scale maps (Soil Conservation Service 1991); processing included calculating an area-weighted average for each map unit based on the percent composition for each soil series in the map unit, and then calculating another area-weighted average for all map units within each county (Iverson et al. 1996).
Total Available Water Capacity (cm, to 152 cm) - average available water-holding capacity in the soil to bedrock or 152 cm (60 inches), whichever comes first. Data were calculated by summing the available water-holding capacity for each layer in the soil horizon, as described for pH.
Soil Types
Alfisol (%) - associated with semiarid to moist environments, mainly under forest or mixed vegetative cover. Data are from STATSGO (Soil Conservation Service 1991)
Aridisol (%) - common in desert environments which are too dry for the growth of mesophytic plants. Data are from STATSGO (Soil Conservation Service 1991)
Entisol (%) - associated with dunes, steep slopes, and flood plains where newly deposited parent material or erosion/deposition rates are faster than soil development. Data are from STATSGO (Soil Conservation Service 1991)
Histosol (%) - contain high organic matter content and no permafrost. Saturated year round. Data are from STATSGO (Soil Conservation Service 1991)
Inceptisol (%) - associated with semiarid to humid environments which undergo moderate degrees of soil weathering and development. Data are from STATSGO (Soil Conservation Service 1991)
Mollisol (%) - contain high organic matter content, associated with grass in climates of moderate to pronounced seasonal moisture. Data are from STATSGO (Soil Conservation Service 1991)
Spodosol (%) - associated with areas of coarse-textured deposits under coniferous forests in humid environments. Data are from STATSGO (Soil Conservation Service 1991)
Ultisol (%) - associated with humid environments where weathering and leaching produce a clay enriched subsoil. Data are from STATSGO (Soil Conservation Service 1991)
Vertisol (%) - contain high content of expanding clay minerals that changes in volume as moisture changes. Data are from STATSGO (Soil Conservation Service 1991)
Elevation
Elevation Coefficient of Variation
Maximum Elevation (m) - average maximum elevation for the counties occupied by the species. Data from USGS 1:250,000 Digital Elevation Model (DEM) files obtained from the USGS internet site (US Geological Survey 1990; available at http://edcwww/cr/usgs.gov/glis/hyper/guide/1_dgr_demfig/states.html
Average Elevation (m) -
Minimum Elevation (m) - average minimum elevation for the counties occupied by the species. Data from USGS 1:250,000 Digital Elevation Model (DEM) files obtained from the USGS internet site (US Geological Survey 1990; available at http://edcwww/cr/usgs.gov/glis/hyper/guide/1_dgr_demfig/states.html
Range of Elevation (m) -
Landscape
Fragmentation Index (Riitters et al. 2002) -
Cropland (%) -
Forest land (%) - a grouping of four classes defined by NLCD consisting of coniferous, deciduous, mixed and wetland forest. (Riitters et al. 2002)
Nonforest land (%) -
Water (%) - all water bodies including ice and snow. (Riitters et al. 2002)
The gray shaded portions of the maps (No Data on legends) had no forest information available, due to one or more of the following: (1) there were no data recorded for any tree species for those counties (e.g., prairie states in the western part of the region), (2) one or more of the four FIA regions (northeastern, north central, southeast, southern) did not report the species in their data base because it was not present in the region (e.g., distinctly northern or southern species), and (3) one or more of the FIA regions do not recognize a particular species name as present in the unit, even though it undoubtedly is present but called something else (e.g. taxonomic confusion like in the hickories (Carya sp.)).