Vegetation mapping at Ocmulgee Mounds National Historical Park: Photointerpretation key and final vegetation map

The University of Georgia Department of Geography’s Center for Geospatial Research (CGR), with the support of the National Park Service (NPS) Vegetation Mapping Inventory (VMI) Program, described and mapped vegetation at Ocmulgee Mounds National Historical Park (OCMU). Mapping was accomplished through collaboration with the NPS Southeast Coast Network (SECN), the North Carolina office of NatureServe (Durham, N.C.), and Atkins North America, Inc. A final vegetation map for Ocmulgee Mounds NHP was created to represent the vegetation occurring within the park during 2011. This product represents the final of four steps necessary to produce an accurate vegetation map based upon aerial photographs. This includes the determination of the community element global (CEGL) codes (2008) and acquisition of aerial imagery (2011), using the aerial imagery, with 130 ground truthing points (2014), to create a draft vegetation map, performing an accuracy assessment (2015), and then using all the available information to create a final vegetation map (2017). The total mapping area was 902.1 hectares (2,275.8 acres [ac]), encompassing the entire boundary of the park plus an additional 500-meter (1,640-foot [ft]) buffered area. The area now, including in Ocmulgee Mounds NHP, has been used by humans for over 17,000 years. This region was heavily deforested in the early 1900s but has recovered in recent decades. The current vegetation of Ocmulgee Mounds NHP shows evidence of previous anthropogenic influences, with many early successional forest species such as sweet gum (Liquidambar styraciflua) and box elder (Acer negundo) and the presence of invasive species, especially Chinese privet (Ligustrum sinense) and Chinese tallow (Triadica sebifera). Because of the past land use history, using the National Vegetation Classification System (NVCS) to the association level was challenging. Determining CEGL codes was particularly difficult because the National Vegetation Classification System was designed for relatively undisturbed vegetation communities. Through the use of 16 NatureServe vegetation plots, color-infrared aerial photos, and data collected in the field, vegetation communities were delineated and assigned attributes. Using dominant vegetation classes and secondary vegetation classes, as well as modifiers to describe the diversity of species, detailed vegetation maps were created for Ocmulgee Mounds NHP. Polygons and attributes within the 500-meter (1,640-ft) buffer were created on a broader scale using a system based on the Anderson Level II classification scheme which includes anthropogenic and land use/land cover (LULC) classes. While within the park, the more detailed vegetation classes were used. The most common class found in Ocmulgee Mounds NHP was Loblolly Pine (White Oak, Southern Red Oak, Post Oak) Southeastern Interior Forest (4232), covering approximately 18% of the park. The smallest class was Upper East Gulf Coastal Plain Cherrybark Oak—Sweetgum Terrace Forest (8585) at less than 1%. The overall lack of a dominant class reflects the subtle topography and anthropogenic influences. A rigorous accuracy assessment was conducted on the 13 map classes within the boundary of OCMU representing floristic types within the NVCS. Results showed an 80% map accuracy and a kappa rating of 77% using 97 accuracy assessment points. The products generated from this project include vegetation maps, a photointerpretation key, summary statistics of each vegetation class, and a detailed geodatabase with digital maps.