An Inventory of the Vascular Plants of Amistad National Recreation Area, Val Verde Co., Texas

Amistad National Recreation Area is a 23,186 ha property in Val Verde County, Texas. A floral inventory was conducted in 2003–2004, producing a checklist of 699 taxa with 99 infraspecific taxa, 686 species, 402 genera, and 106 families. There are 651 native taxa and 48 introduced. No federally or state listed plants were documented. Seventeen species of conservation concern were verified within the park. Thirteen taxa endemic to Texas were recorded. Plant communities were also noted and compared to those previously reported for the site. Amistad National Recreation Area (Amistad NRA) is located in southwest Texas along the U.S.-Mexico border near the town of Del Rio, Texas. The recreation area extends along the Rio Grande from above Langtry to just above Del Rio, and up two tributaries of the Rio Grande, the Pecos, and Devils Rivers, for dozens of miles. The recreation area was created after the construction of Amistad Dam that was built in 1969 below the confluence of the Rio Grande and the Devils River. Lake Amistad International Reservoir has approximately 1,432 km (890 mi) of shoreline with numerous coves and inlets, 869 km (540 mi) in the United States and 563 km (350 mi) in Mexico. The park’s boundary is mostly unfenced. Amistad NRA is located in Val Verde County, Texas (Figure 1) and consists of 23,186 ha (57,294 ac), including areas covered by the reservoir (NPS 2006). Except for some upland areas beyond the main body of the reservoir (including five Hunt Areas), the actual land area of the NRA fluctuates with changing reservoir levels. The national recreation area’s boundary is generally defined as the reservoir surface and shore area up to the 348.8-meter (1,144.3-foot) elevation contour above mean sea level, with a pool conservation level contour of 340.5 meter (1,117 feet) above mean sea level. Water in the reservoir is used for municipal and irrigation purposes for communities downstream along the Rio Grande (NPS 2004). The climate of Amistad NRA is semiarid, with hot summers and mild dry winters (Golden et al., 1982; Natural Fibers Information Center 1987). Rainfall occurs primarily in two time periods: April through June and September through October, with .80% of the annual precipitation occurring from April to October. Average annual precipitation in Del Rio is 469 mm (18.5 in). However, precipitation tends to fall erratically, with monthly and yearly totals often straying far from the average. During the August 1998 flood, 432 mm (17.02 in) of rain, almost the average annual rainfall, fell during one day, in contrast to the average annual precipitation in 1956 that was only 110.2 mm (4.34 in). During the field sessions of this study (April 2002 to October 2003), a year long drought was broken, and precipitation was above average most months. Average monthly temperatures vary from 10uC (50u F) in winter to 27uC (81u F) in summer. Temperatures can be quite hot, especially in the summer, with an average of 124 days over 32uC (90uF). Freezing temperatures occur on average only 19 days a year (National Weather Service 2003). Geologically Amistad NRA is fairly homogeneous (Bureau of Economic Geology 1977). Most of the outcropping and underlying rock is Cretaceous limestone. The Salmon Peak and Buda limestones are the most common, while the Del Rio clay (calcareous and gypsiferous clay), is locally 8 LUNDELLIA DECEMBER, 2013 LUNDELLIA 16:8–82. 2013 common at some sites. Along the narrow Rio Grande corridor of the park, upstream from the confluence with the Pecos River, the Devils River limestone replaces the others as the most common rock type. Some minor outcrops of the Eagle Ford formation (shales, siltstones, and limestone) and the Pliocene or Pleistocene Uvalde gravel formation also occur within Amistad NRA boundaries. Most of the soils within Amistad NRA are shallow, rocky and alkaline (Golden et al. 1982). The rivers and drainages that have not been permanently flooded contain primarily riparian type soils. Along the Rio Grande, the soils (Rio Grande Series) are deep, loamy and silty. Near the end of the Amistad NRA boundary along the Devils River, the soils are unstabilized, nearly barren, sandy, gravelly, rocky sediments (Riverwash soil map unit) that wash in from the surrounding limestone hills. Areas of exposed limestone bedrock also occur. The rest of the Devils River within the recreation area as well as the drainages of San Pedro Creek are in the Dev Series (very gravelly clay loams). The Pecos River (within the recreation area boundary) has little soil development, and is mapped as LangtryRock outcrop association. Although the association is mostly composed of limestone rock outcrops, Langtry soils are rocky clay loams. The upland soils of Amistad NRA also vary by location. From the park’s uppermost reaches on the Rio Grande to Langtry, the soils are primarily the Mariscal-Lozier association (shallow, rocky loams) and the Lozier-Shumla association (shallow loamy to gravelly loamy soils). From Langtry to Seminole Canyon, the soils are the same as those along the Pecos, the Langtry-Rock outcrop association. Below Seminole Canyon to Evans Creek, the Langtry-Rock FIG. 1. Amistad National Recreation Area with plot locations. NUMBER 16 POOLE: PLANTS OF AMISTAD NATIONAL RECREATION AREA 9