Dick D. Heller, Jr.

RIO GRANDE-FALCON THORN WOODLAND. The Rio Grande-Falcon Thorn Woodland, also called Chihuahuan Thorn Forest or Falcon Woodland, extends from Falcon Dam southeast along the Rio Grande nineteen miles past Roma to Rosita in Starr County. It is one of eleven biotic communities in the Matamoran District, Tamaulipan biota, southern Texas. The 24,000-acre area is the largest undisturbed remnant of tropical-thorn woodland in the United States and is ranked fifth of the top 100 nationally significant fish and wildlife areas. The unique feature of this community is the riparian zone, the river on one side and desert scrub on the other. Habitat types are black willow-Berlandier ash (Rio Grande Riparian), 20 percent; thornscrub association, 30 percent; and mesquite-granjeno association, 50 percent. The riparian zone varies in width from a steep bank to a quarter-mile-wide flood terrace. The riparian zone includes black willow (Salix nigra), Montezuma bald cypress (Taxodium mucronatum), Berlandier ash (Fraxinus berlandieri), Texas ebony (Pithecellobium flexicaule) and mesquite (Prosopis gladulosa). The only known grove of Montezuma bald cypresses in the United States occurs here. Three rare plants are known: Gregg wild buckwheat (Eriogonum greggi), slashleaf heartseed (Cardiospermum dissectum), and Amoreuxia wriqhtii. Falcon Thorn Woodland provides habitat for than 300 bird species, 50 mammal species, 50 reptile species, and 20 species of amphibians. Many of these species are either peripheral to the United States or listed as threatened or endangered by the Texas Organization for Endangered Species. Notable birds in the area include the brown jay (Psilorhinus morio), the only breeding populations in the United States of the hook-billed kite (Chondrohierax uncinatus), the plain chachalaca (Ortalis vertula), the gray hawk (Buteo nitidus), the Altamira oriole (Icterus gularis), Audubon's oriole (Icterus graduacauda), the green kingfisher (Chloroceryle americana), the ringed kingfisher (Ceryle torquata), ferruginous owl (Glacidium brazilianum), and the elf owl (Micrathene whitneyi). Other uncommon wildlife found in Falcon Woodland includes the Mexican burrowing toad (Rhinophrynus dorsalis), giant toad (Bufo marinus), and Texas horned lizard (Phyrnosoma cornutum). Endangered species include the peregrine falcon (Falco peregrinus), ocelot (Felis pardalis), and jaguarundi (Felis yagouaroundi). The Lower Rio Grande Valley National Wildlife Refuge, established in 1979, hopes to acquire the entire area but had managed to obtain only three small tracts, totaling 100 acres, by 1990. The state has an additional eighty acres at Prieta Bend, and the International Boundary and Water Commission holds a large tract below the dam.


W. Frank Blair, "The Biotic Provinces of Texas," Texas Journal of Science 2 (March 1950). U.S. Fish and Wildlife Service, Concept Plan: Unique Wildlife Ecosystems, Texas (Albuquerque, New Mexico, 1979). Rio Grande-Falcon Thorn Woodland (Natural Area Survey 13, LBJ School of Public Affairs, University of Texas at Austin, 1976).

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The following, adapted from the Chicago Manual of Style, 15th edition, is the preferred citation for this article.

Handbook of Texas Online, Dick D. Heller, Jr., "RIO GRANDE-FALCON THORN WOODLAND," accessed December 14, 2019,

Uploaded on June 15, 2010. Modified on January 25, 2019. Published by the Texas State Historical Association.
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