The Feather River was mapped using 2018 National Agricalutural Inventory Program (NAIP) imagery, and using a classification developed by the California Native Plant Society (CNPS) based in the National Vegetation Classification System (NVCS). A report describing mapping methodology for a similar project can be found here: https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=184992.For more information about California's classification, see https://vegetation.cnps.org/.Changes in a remap effort can occur due to several factors, some due to physical change and some due to non-physical change. Examples of factors that represent physical change are: stand maturation or decadence, fire, erosion, deposition, anthropogenic disturbances such as scraping/clearing, urban development, agricultural development, and restoration. Non-physical changes include: improvement in imagery quality, incorrect original mapping, imagery shifts, improvement of older linework, and change in level mapped (classification). Imagery quality continues to improve with time, which allows the photointerpreter to better determine which species are present and in what amounts to determine its best classification. A photointerpreter could also disagree with the previous mapper’s decisions and may change the classification in the remapping effort. A more subtle map change, which does not affect the acreages significantly, is when the photointerpreter improves old linework to make it better fit the classification type visually. Also, when the NAIP imagery is ortho-rectified, in some years it does not perfectly align with the year it is being compared to and linework needs to be shifted/redrawn. Lastly, a photointerpreter may have remapped an Alliance at the Group level due to lack of confidence at the Alliance level, and vice versa the interpreter may have mapped an Alliance that was previously mapped at Group level due to better confidence at that level. All of these factors should be taken into consideration when using and comparing these data to previous efforts.
