The following variables have been assessed from the FIA data:
Number of counties: the total number of counties for which the species has been recorded with FIA data.
Diameter, cm: the average diameter for the species across each plot, assessed on a per plot basis. The number of plots are also given, which occur in the number of counties given in the above field.
Growth rate, cm2 basal area/yr: based on remeasurement plots only (a subset of the total number of plots), this variable is calculated as the difference between basal areas for each species measured on plots at two sampling intervals. Usually, the time between measurements is about 10 years. To remove plots that show a negative growth (e.g., the plot was harvested), only plots with positive growth were included in the distributional curve.
Annual Temperature, C: average annual temperature for the counties occupied by the species. Data from USEPA (1993).
January Temperature, C: average January temperature for the counties occupied by the species. Data from USEPA (1993).
Precipitation, mm: average annual precipitation for the counties occupied by the species. Data from USEPA (1993).
Potential evapotranspiration, mm/month: average monthly potential evapotranspiration for the counties occupied by the species. Data from ESEPA (1993).
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
Slope, percent: 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).
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.
Permeability, 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.
Organic matter, percent: the percentage of organic matter in the surface layer of the soil. Data are from STATSGO, and calculated as for slope.
Clay, percent: the percentage clay in the soil column to a depth of 60 inches (152 cm) or the depth to bedrock. Data are from STATSGO, and calculated as for pH.
Water-Holding Capacity, cm/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.
Iverson, L.R.; Prasad, A.; Scott, C.T. 1996. Preparation of forest inventory and analysis (FIA) and state soil geographic data base (STATSGO) data for global change research in the eastern United States. In: Hom, J.; Birdsey, R.; O'Brian, K. Proceedings, 1995 meeting of the Northern Global Change Program; 1995 March 14-16; Pittsburgh, PA. Gen. Tech. Rep. NE-214, Radnor, PA:, U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station: 209-214.
Soil Conservation Service. 1991. State soil geographic data base (STATSGO) data users guide. Misc. Publ. 1492. Washington, DC.: U.S. Department of Agriculture, Soil Conservation Service. 88 p.
U.S. Environmental Protection Agency. 1993. EPA-Corvallis model-derived
climate database and 2xCO2 predictions for long-term mean monthly temperature,
vapor pressure, wind velocity and potential evapotranspiration from the
Regional Water Balance Model and precipitation from the PRISM model, for
the conterminous United States. Digital raster data on a 10 x 10 km, 470
x 295 Albers Equal Area grid, in "Image Processing Workbench" format. Corvallis,
OR: U.S. Environmental Protection Agency, Environmental Research Laboratory.