Vegetation Classification and Mapping Project Report - USGS

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USGS-NPS Vegetation Mapping Program Colonial National Historical Park Tree-of-Heaven Forest (0%), and Tidal Freshwater Marsh (60%). Four accuracy assessment points that fell in areas mapped as Coastal Plain Loblolly Pine – Oak Forest were not classified in agreement with the map. These errors can be attributed to below minimum mapping unit inclusions of other vegetation types within the target polygons and incomplete inspection of polygons. Since the compositional data collected in accuracy assessment support the original mapped class, a misunderstanding of the key or descriptions seems a likely cause of error. Only 25% of the accuracy assessment points that fell into Coastal Plain Calcareous Ravine Forest were in agreement with the map. This is an understandable error since confirmation of this vegetation in the field can depend on the visibility of several indicator species that are only apparent early in the growing season. Modifications were made to the local descriptions noting that, late in the season when some herb species are not evident, Coastal Plain Mesic Calcareous Ravine Forest may be confused with Mesic Mixed Hardwood Forest. The one polygon of Successional Black Walnut Forest that was classified as Successional Mixed Scrub was transitional in composition and structure and could not be confidently reclassified based on accuracy assessment data. The error of omission for Successional Tree-of-Heaven Forest is 0% since it is mapped as only one polygon and the polygon was identified as Successional Tuliptree - Loblolly Pine Forest during accuracy assessment. Examination of accuracy assessment data revealed that only a small portion of the polygon was observed and that tree of heaven (Ailanthus altissima) may have been misidentified as black walnut (Juglans nigra). Four polygons mapped as Tidal Freshwater Marsh were identified as other tidal marsh map classes in accuracy assessment. Vegetation at some of these locations was transitional between concepts and difficult to classify from accuracy assessment data. The error of commission exceeds 80% for all classes in the final vegetation map except Coastal Plain / Piedmont Floodplain Swamp Forest (Green Ash - Red Maple Type) (50%) and Mesic Mixed Hardwood Forest (77%). One area mapped as Coastal Plain / Piedmont Small- Stream Floodplain Forest and one area mapped as Non-Riverine Saturated Forest were incorrectly identified as Coastal Plain / Piedmont Floodplain Swamp Forest (Green Ash – Red Maple Type) in the accuracy assessment. These map classes can be difficult to distinguish in the field, particularly in ecotonal or disturbed areas, and on photography since all are deciduous wetland forests that have similar photosignatures. Three areas mapped as Coastal Plain Mesic Calcareous Ravine Forest and three areas mapped as Successional Tuliptree – Loblolly Pine Forest were identified as Mesic Mixed Hardwood Forest in accuracy assessment. On the ground, Coastal Plain Mesic Calcareous Ravine Forest may be confused with Mesic Mixed Hardwood Forest, particularly late in the growing season when some of the indicator species are not visible. The two map classes are both deciduous upland forests with similar canopy composition and similar landscape positions, and thus could easily be confused in photo interpretation. Confusion between Successional Tuliptree - Loblolly Pine Forest and Mesic Mixed Hardwood Forest both on the ground and in photointerpretation is also understandable since some stands of these map classes can be compositionally similar, and both map classes can have virtually identical photo signatures. The error of commission could not be calculated for Semipermanent Impoundment or Sucessional Mixed Scrub since these classes were not included in the accuracy assessment. Both classes are present in the contingency matrix to indicate when accuracy assessment observations identified sample points as these classes. 66
USGS-NPS Vegetation Mapping Program Colonial National Historical Park Vegetation Map Production The final vegetation map for Colonial National Historical Park is shown in Figures 10, 11, and 12 and a summary of the map class distribution and abundance is provided in Table 14. The mapping boundary was based on park boundary data obtained from Colonial National Historical Park in May 2003. The mapping boundary includes lands under a scenic easement at Swanns Point and it excludes the Cheatham Annex, an area that returned to US Navy ownership in February 2004. The vegetation map was clipped at the park boundary because areas outside the park were not surveyed or included in the accuracy assessment. The original vegetation map was revised based on the accuracy assessment sampling data to correct certain map class errors and create a more accurate map. Specific map edits are listed in the Accuracy Assessment results section of ths report. Polygons that are attributed with Anderson Level II class 14 (Transportation, Communication, and Utilities) are further attributed in the comment field of the vegetation map attribute table to identify what finer feature they represent (transportation or utilities). The map class Cultural Meadow includes mowed roadsides larger than 0.5 ha. Those polygons representing mowed roadsides are indicated as such in the comment field of the map attribute table. Mowed roadsides smaller than 0.5 hectare are included either with the adjacent road (Anderson Level II class 14 - Transportation, Communication, and Utilities) or the adjacent vegetation polygon. Cultural Meadow polygons not representing mowed roadsides are indicated with the term “field” in the map attribute table. Other Urban or Built-up Land polygons are further distinguished in the comment field of the map attribute table if they represent a golf course, riprap, or a spillway. Disturbed examples of Non-Riverine Saturated Forest that do not have the typical species composition are labeled as "disturbed" in the comment field of the vegetation map attribute table. A field was included in the map attribute table to indicate which United States Fish and Wildlife Service (USFWS) wetland system (sensu Cowardin et al. 1979) a map class represents. Polygons representing wetland formations (i.e. those with temporarily flooded, seasonally flooded, saturated, semipermanently flooded, or tidal hydrologic modifiers) are tagged to the appropriate system in the USFWS wetland classification. Polygons representing vegetation that is not classed as a wetland have the value of “upland” in this field. Polygons representing deepwater areas without emergent vegetation are labeled as “open water” in this field. Maps of polygons representing the wetland map classes are shown in Figures 13 and 14. These maps do not show jurisdictional wetlands, but rather the distribution of wetland map classes with USNVC formations containing wetland modifers. The hydrology of the map class may not represent the hydrology on the ground and small areas of wetlands may be included within polygons classed as “upland”. Project Deliverables Final products of the vegetation mapping project are shown in Table 15. All products have been delivered to the National Park Service by the Virginia Department of Conservation and Recreation, Division of Natural Heritage with this report or at an earlier date by NCSU-CEO. 67
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Vegetation Classification and Mapping Project Report - USGS

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