Channel Islands Vegetation (2017)

The base for georeference and photo interpretation of the vegetation mapping was the natural color 6-inch resolution digital orthophoto imagery flown in October 2012 for the Channel Islands Regional GIS Collaborative. The minimum mapping unit (MMU) resolution for the project is .5 hectare. 

The National Vegetation Classification Standard floristic vegetation classification was the basis of criteria for the mapping classification and map class descriptions of vegetation types; and was derived from vegetation classification alliance and association characteristics gleaned from the Channel Islands National Park floristic Vegetation Descriptions, the floristic Vegetation Key, and the corresponding classification field sampled data. Environmental factors such as elevation, slope, and aspect also played an important part in the photo interpretation decision-making process.

The mapping was conducted through photo interpretation of the aerial imagery and field reconnaissance. In the ”photo interpretation process”, the photo interpreter applies his or her understanding of photo signature and knowledge of the geographic characteristics of ground features to formulate a reasoned decision about how to represent a feature and what to call it. The “mapping process” involves the creation of the digital geodatabase through the use of computer hardware and software using an on-screen heads-up digitizing method. Each polygon was assigned the appropriate attribute code string: Vegetation Type (MapCode) and Percent Cover types (ConiferCover, HardwoodCover, ShrubCover, and HerbaceousCover). A Comment field was also used to add any pertinent information, such as significant species present not accounted for in the alliance or association name.

The final mapping classification for Santa Rosa, San Miguel, and Anacapa Islands contains 48 alliances and 10 Mapping Units types.  A total of 35 alliances were mapped on Santa Rosa Island, in addition to 3 Group level and 10 Mapping Unit types; San Miguel Island has 20 alliances, 2 Group level, and 7 Mapping Unit types; and Anacapa Island has 19 alliances, 1 Group level, and 5 Mapping Unit types.  Mapping to the association was a Park Special task.  There were 88 associations included in the mapping classification for the three islands.  However, only San Miguel and Anacapa Islands were mapped to the association level where possible. A total of 35 associations were mapped on San Miguel Island, and 26 were mapped on Anacapa Island.  For Park Special purposes only 3 specific association level types were mapped for Santa Rosa Island.

For Santa Rosa and San Miguel Islands the resulting vegetation map database was then assessed for accuracy by the Park through a formal Accuracy Assessment (AA) step. Anacapa Island, however, being very small in size and of limited accessibility, did not require a formal AA as the mapping used a Census approach, by which the Park field crew visited each polygon and recorded the vegetation information, which was used to revise the polygon attributes as needed. The final AA result of Overall Accuracy was 88.0% for Santa Rosa Island and 84.9% for San Miguel Island.