Vegetation - Napa County Update 2016 [ds2899]

The earlier map used black and white digital orthophoto quadrangles from 1993, with a pixel resolution of 3 meters. This image was delineated using a heads up digitization technique produced by ASI (Aerial Services Incorporated). The resulting polygons provided vegetation and landcover attributes following the classification system used by California State Department of Fish and Wildlife mappers in the Manual of California Vegetation. The 2004 effort included a brief field campaign in which surveyors drove accessible roads and verified or corrected the dominant vegetation of polygons adjacent to roadways or visible using binoculars. There were no field relevé or rapid assessment plots conducted. This updated version uses a 2016 edition of 1 meter color aerial imagery taken by the National Agriculture Imagery Program (NAIP; [https://www.fsa.usda.gov/programs-and-services/aerial-photography/imagery-programs/naip-imagery/index]) as the base imagery. It therefore permits an assessment of the change in the patterns of vegetation over 23 years in the county. In consultation with the county we decided to use similar methods to the previous mapping effort, in order to preserve the capacity to assess change in the county over time. This meant forgoing recent data and innovations in remote sensing such as were used in a concurrent project that mapped Sonoma County including the use of LiDAR and Ecognition’s segmentation of imagery to delineate stands. However, the use of such technologies would have made it more difficult to track land cover change in Napa county, because differences in publication dates would not be definitively attributable to actual land cover change or changes in methodology. The overall cost of updating the map in the way was approximately 20% of the cost of the Sonoma vegetation mapping program. Therefore, we started with the original map, and on-screen inspections of the polygons to determine if change had occurred. If so, the boundaries and attributes were modified in the new edition of the map. We also used the time series of imagery available on Google Earth, and the high resolution imagery available through ArcMap to further inspect many edited polygons. We conducted 3 rounds of quality assessment/quality control exercises. Funding was not available to do field assessments, but we incorporated field expertise for the Angwin Experimental Forest, reviewed vegetation types identified in the Knoxville Wildlife Area from a 2014 map incorporating 29 of them, and used overlap with the Sonoma Vegetation Map to assess some polygons thought to contain redwood trees (Sequoia sempervirens) along the western side of Napa County. The Angwin Experimental Forest was mapped by Peter Lecourt from Pacific Union College. He identified several polygons of redwoods in what are potentially the eastern-most extent of that species. We reviewed those polygons with him and incorporated some of the data from his area into this map. The 2014 Knoxville Vegetation map was developed by California Department of Fish and Wildlife. It was made public in February of 2019, close to the end of this project. We reviewed the map, which covers part of the northeast portion of Napa County. We incorporated polygons and vegetation types for 18 vegetation types including the rare ones, we reviewed and incorporated some data for another 6 types, and we noted in comments the presence of another 5 types. There is a separate report specifically addressing the incorporation of this map to our map. Dr Amber Manfree has been conducting research on fire return intervals for parts of Napa County. In her research she identified that large piles of rocks are created when vineyards are put in. These are mapable features. She shared the locations of rock piles she identified, which we incorporated into the map. The Sonoma Vegetation Map mapped some distance into the western side of Napa County. We reviewed that map’s polygons for coast redwood. We then examined our imagery and the Google imagery to see if we could discern the whorled pattern of tree branches. Where we could, we amended or expanded redwood polygons in our map. The Vegetation classification systems used here follows California’s Manual of California Vegetation and the National Vegetation Classification System (MCV and NVCS). We started with the vegetation types listed in the 2004 map. We predominantly use the same set of species names, with modifications/additions particularly from the Knoxville map. The NVCS uses Alliance and Association as the two most taxonomically detailed levels. This map uses those levels. It also refers to vegetation types that have not been sampled in the field and that has 3-6 species and a site descriptor as Groups, which is the next more general level in the NVCS classification. We conducted 3 rounds of quality assessment/quality control exercises.