Vegetation Classification and Mapping Project Report, San Antonio Missions National Historical Park

Cogan, Dan; Cogan Technology Inc.

San Antonio Missions National Historical Park (SAAN) encompasses approximately 844 acres in the city of San Antonio and rural Wilson County, Texas. The park preserves and celebrates the largest collection of Spanish colonial resources in the U.S., including four missions, two acequias (irrigation ditches), and one ranch remnant. The four missions are located in the southern portion of San Antonio along the San Antonio River and the ranch site is located approximately 5 miles southwest of Floresville, Texas and 35 miles southeast of San Antonio. SAAN was created to protect and commemorate these historical structures and in addition it also contains rich and varied natural resources including native flora common to the Tamaulipan thornscrub and southern tallgrass prairie ecoregions. To better understand the distribution of these plant assemblages the National Park Service’s (NPS) Southern Plains Inventory and Monitoring Network (SOPN) in conjunction with the NPS’s Gulf Coast Inventory and Monitoring Network (GULN) begun a vegetation mapping and classification effort at SAAN in 2005. A three-year program was initiated to complete the task of mapping and classifying the vegetation at SAAN. Phase one, directed by the Botanical Research Institute of Texas (BRIT) in conjunction with NatureServe developed a vegetation classification using the National Vegetation Classification System (NVCS). Phase two, directed by the U.S. Bureau of Reclamation’s (BOR) Remote Sensing and GIS group in conjunction with Cogan Technology, Inc. (CTI) produced a digital vegetation map. To classify the vegetation, 35 representative plots located throughout the approximately 6,784 acre project area (parks + environs) were sampled during the summer of 2005. Analysis of the plot data by NatureServe in the winter of 2005-2006 identified 10 distinct plant associations and alliances, one of which was newly described in the National Vegetation Classification (NVC). In addition, CTI described an additional alliance and two distinctive stands of vegetation (i.e. Park Specials) that primarily occurred outside of the park boundary in the environs. Descriptions and a field key for all 13 unique plant assemblages for SAAN are included in this report. To produce the digital map, a combination of 1:12,000-scale ortho imagery acquired in 2003, 2004, and 2005 and all of the GPS-referenced ground data were used to interpret the complex patterns of vegetation and land-use. All imagery was acquired from the U.S. Department of Agriculture - Farm Service Agency’s Aerial Photography Field Office and the National Agriculture Imagery Program. In the end, 32 map units (13 vegetated and 19 land-use) were developed and directly cross-walked or matched to corresponding plant associations and land-use classes. All of the interpreted and remotely sensed data were converted to Geographic Information System (GIS) databases using ArcGIS© software. Draft maps were printed, field tested, reviewed, and revised. One hundred-twenty four accuracy assessment (AA) data points were collected in 2006 and used to determine the map’s accuracy. After final revisions, the accuracy assessment revealed an overall thematic accuracy of 89%.

Vegetation Classification and Mapping Project Report, San Antonio Missions National Historical Park

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