- Suitability Maps
- Species Selection Tool
Species tolerance functions were developed for each forage species for three climate variables (30-year average annual precipitation, 30-year average July maximum temperature, and 30-year average annual extreme low temperature) and three soil factors (pH, drainage class, and salinity). For each variable and for each species, the curves were fitted using estimated yield data across the range of values for the given variable. Climate variables were fitted using Logistic curves. For soil factors, pH was fitted with a Gaussian curve, and salinity was fitted with a critical exponential function. Although soil drainage is a categorical characteristic, a function was fitted to a critical exponential function using estimated relative yield values based on suitable ranges of drainage specified in the NRCS Range and Pasture handbook.
The coefficients were developed using R Studio and model equations were compiled into a single table as input to a python script written for ESRI's GIS software, ArcGIS. The script uses spatial data for each of the climate and soil variables as inputs, and together with the table of equation coefficients, produces spatial outputs representing percent yield for each of the forage species and each climate and soil factor. This design ensures that the script can easily be re-run with updated equation coefficients as the relationships between the environmental variables and yield are refined.
The percent yield layers were classified by the script into four suitability classes:
1. 0-25% - Not suitable
2. 25%-50% - Marginally suitable
3. 50%-75% - Moderately suitable
4. 75%-100% - Suitable
The script produces three "hybrid" suitability layers based on combinations of the three climate variables, the three soil variables, and all six climate and soil variables together. These combined suitability layers were created by selecting for every location the lowest suitability value of the included variables, with overall suitability for a species limited by the most restrictive factor. A map atlas was created in ArcGIS to produce Jpeg maps of each species for each soil, climate, and "hybrid" variable, resulting in 9 Oregon and 9 US maps for each species: