Vegetation Classification and Mapping of Valley Forge National Historical Park

Podniesinski, Greg

Final report for the Valley Forge National Historical Park Vegetation Inventory project. The vegetation of Valley Forge National Historical Park was mapped during 2000 and 2001 as part of the U.S. Geological Survey (USGS) / National Park Service (NPS) Vegetation Mapping Program. The goal of the mapping effort was to produce an up-to-date digital geospatial vegetation database for the park. New aerial photography was obtained for the park in spring 1999 by Air Photographics, Inc., and converted to a digital orthophoto mosaic image by the North Carolina State University Center for Earth Observation (CEO) in winter 1999-2000. CEO interpreted the photography and developed a digital formation-level vegetation map. Pennsylvania Science Office of The Nature Conservancy (PSO-TNC) sampled 80 vegetation classification plots during the summer of 2000. Data analysis identified eight natural vegetation types and 13 anthropogenic types (ranging from managed grasslands to hard infrastructure such as transportation corridors). Vegetation analysis information was used by CEO to reclassify formation-level polygons to develop an association-level vegetation map. Accuracy assessment of the association-level map was performed by PSO-TNC using 308 sampling points distributed across all polygon types according to vegetation mapping program guidelines. Overall accuracy was 82.8%, adjusted accuracy (Kappa index, to account for correct classifications occurring by chance), was 81.2% ± 3.8% (90% C.I.). Approximately 50% of the mapping errors were associated with four pairs of associations or cover types: Cropland and Grassland (tall grass), Dry Oak Forest and Tuliptree – Oak Forest, Grassland (mowed) and Grassland (tall grass), and Riverine Floodplain Forest and Silver Maple Floodplain Forest. NatureServe provided crosswalk information between park vegetation types and National Vegetation Classification System (NVCS) association types as well as association descriptions. The resulting vegetation mapping product represents current vegetation types within the park and is consistent with the standards of the USGS/NPS Vegetation Mapping Program.Natural vegetation types that are relatively undisturbed were easily crosswalked to the corresponding NVCS association. Some natural vegetation types characterized by past anthropogenic disturbance or landuse, especially the Northeastern Modified Successional Forest, initially had no NVCS equivalent. An NVCS association has been developed for the Northeastern Modified Successional Forest, as it has been found in all other national parks in Pennsylvania. The Successional Old Field / Shrubland type remains a local type with no NVCS crosswalk. Anthropogenic vegetation types were crosswalked to the NVCS where possible, usually as cultivated or planted vegetation types.The most common natural vegetation types were Northeastern Modified Successional Forest (190 ha, 11.4% of mapped area) and Tuliptree - Oak Forest (110 ha, 6.8% of mapped area). The least common natural vegetation type was the Chestnut Oak – Black Birch Talus Slope (0.39 ha, <0.01% of mapped area). The most common managed or planted vegetation types were Grassland (mowed and tall grass combined) (538 ha, 32.3% of the mapped area) and White Pine Plantation (155 ha, 9.3% of the mapped area). None of the vegetation types described at Valley Forge National Historical Park are rare in Pennsylvania.Natural vegetation quality within the park ranged from poor to fair. In general, heavy deer browse has created a depauperate herb and shrub layer in most vegetation types and reduced or eliminated forest regeneration. Exotic plant species are a significant problem in recently disturbed area, successional forests, and old fields, as well as mesic forest types (e.g., Tuliptree – Oak Forests and floodplain forests).

Vegetation Classification and Mapping of Valley Forge National Historical Park

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