Amistad National Recreation Area (AMIS) covers approximately 57,000 acres (23,000 hectares) in south Texas along the United States (U.S.) border with Mexico. Under a joint International Agreement in 1964, the Amistad Dam was constructed at the confluence of the Rio Grande and Devils Rivers impounding the waters and creating the Amistad Reservoir. In 1990, the National Park Service (NPS) was directed to manage the U.S. surface waters and surrounding lands as a national recreation area. The resulting AMIS park unit contains many unique vegetation elements from three converging ecoregions. Together they combine to form various upland and riparian woodland, shrubland, and herbaceous plant communities. Past and present land-use practices such as ranching and development along with natural disturbances from flooding and drought have also influenced the vegetation at AMIS. In 2010 the National Vegetation Inventory Program (NVIP) and the NPS Chihuahuan Desert Inventory and Monitoring Network (CHDN) began a vegetation inventory effort to better understand and document the vegetation diversity at AMIS.
An eight-year, six-phase project was begun in 2010 to complete the inventorying and mapping of the vegetation at AMIS. Phase one, conducted by Cogan Technology, Inc. (CTI), reviewed the existing vegetation data, summarized the previous classification efforts, and created a new sampling plan. In 2012, ecologists affiliated with the Lady Bird Johnson Wildflower Center (LBJWC) used the sampling plan to collect field data at 100 classification plot and two observation point locations. Field data was then entered into the NVIP-specific PLOTS database and reviewed by CHDN staff. In phase three, CTI analyzed the PLOTS data to classify 31 plant associations using the revised U.S. National Vegetation Classification (rUSNVC) standard. During phase four, CTI created 50 map units (37 vegetated and 13 land-use/land-cover types) to produce a detailed digital vegetation map layer. Phase five was the accuracy assessment (AA), where LBJWC field crews collected data at 562 AA points that were stratified by map class and randomly placed throughout the project area. In 2019, CTI completed the project and delivered the final products to the NVIP.
The resulting spatial database and vegetation map layer for AMIS was created from high-resolution 2015 Texas Orthoimagery Program (TOP) imagery and ancillary data. By comparing the signatures on the imagery to the field data, map units were used to delineate the vegetation alliances and associations into homogeneous polygons. The interpreted vegetation polygons were then digitized into a Geographic Information System (GIS) layer that was field-tested, reviewed, and revised. The final AMIS vegetation map was assessed for overall thematic accuracy at 87.0% with a Kappa value of 87.3%.
Products developed for AMIS are described and presented in this report and stored in the accompanying project digital files. Project deliverables include the final AMIS Vegetation Inventory Report, the AMIS Spatial GIS Geodatabase, Digital Field Photos, Metadata, Vegetation Descriptions, and the Field Key to the Vegetation Associations. For a full listing of the AMIS products available to download please visit the National Park Vegetation Inventory Product website.
