Siletz Estuary Plant Community (Vegetation) Mapping - Geospatial Data, 2001

This study mapped twelve wetland plant communities (or “alliances”) and 59 subcommunities (or “community elements”) in 252 ha (623 A) of tidal and formerly tidal wetlands within the Siletz estuary. The target shapefile polygon size for the GIS mapping project was 0.8 to 2 ha (1 to 5 A). Within the study area, plant communities (as generally defined by estuarine ecologists) tended to occupy larger areas (over 2 ha). Therefore, each polygon was assigned both to a plant community, and to a smaller, more closely defined "subcommunity" that was characterized by a particular group of dominant plant species. The average size of a polygon (subcommunity) on the final map was about 1.5 ha (3.7 A), but about a third of the polygons were under 0.8 ha (2 A) in size. When using the plant community maps provided in this report, it is important to remember that the community descriptions are based on plant community composition as viewed from onsite, within the community. The visual impression of a plant community may be quite different from offsite (for example, from a nearby road) (see Visually dominant species below). Onsite investigation of each plant community is recommended when reviewing plant communities described in this report or when conducting more detailed analyses. The mapping provided in this report is intended for two main uses: preliminary planning (for instance, as an aid to restoration project planning); and environmental stratification for detailed quantitative sampling (see Stratification recommendations below). The mapping provided is not appropriate for regulatory purposes or for quantitative analysis of vegetation change