Riparian Vegetation of the Lower Rio Grande

The riparian vegetation of the lower reach of the Rio Grande was studied at 7 locations using 3 line intercepts at each location. There were no trees at the mouth of the river and the vegetation was similar to that found along the Laguna Madre shore of barrier islands. Mesquite (Prosopis glandulosa) was the dominant tree near the coast and in the western section of the river near Falcon Dam. Sugar hackberry (Celtis laevigata) was the dominant tree species at all other sites except at Santa Ana National Wildlife Refuge, where cedar elm (Ulmus crassifolia) and anacua (Ehretia anacua) were the dominant trees. Granjeno (Celtis pallida) was a dominant shrub throughout the riparian corridor. The dominant trees and shrubs appeared to be replacing themselves. Species similarity in the tree, shrub, and ground layers was greater among transects at a given site than between sites. The introduced Guinea grass (Panicum maximum) and buffel grass (Pennisetum ciliare) were the dominant species in the ground cover, displacing native species. - La vegetación riparia de la sección baja del Río Bravo fue estudiada en siete localidades utilizando tres líneas de intercepción en cada localidad. No hay árboles en la desembocadura del río y la vegetación es semejante a la de la orilla de las islas barrera de la Laguna Madre. Mesquite (Prosopis glandulosa) es el árbol dominante cerca de la costa y en la sección occidental del río cerca de la Presa Falcón. El palo blanco (Celtis laevigata) es la especie de árbol dominante en todos los demás sitios excepto en el Refugio Silvestre Nacional de Santa Ana donde el olmo (Ulmus crassifolia) y la anacua (Ehretia anacua) son los árboles dominantes. Granjeno (Celtis pallida) es el arbusto dominante en todo el corredor ripario. Parece que los árboles y arbustos dominantes se están reemplazando. La semejanza de especies entre árboles, arbustos y cobertura de tierra es más alta entre transectos en un sitio que entre sitios. Las hierbas exóticas, Panicum maximum y Pennisetum ciliare, son las especies dominantes de la superficie terrestre, desplazando a las especies nativas

Phytogeography of South Padre Island, Texas

The phytogeographic affinities of the native flora of South Padre Island, Texas, are analyzed and the probable dispersal agent(s) for each species identified. The native flora consists of 99 species and 44% of the species also occur on the adjacent Texas mainland; 28% of the native species have tropical affinities. Only three species have probably dispersed from the island to the mainland. Two species may be endemic to Padre Island and the Tamaulipan barrier islands. Most of the tropical species have reached the island by oceanic drift, but birds are the most important dispersal agent for the native species. Man is responsible for the introduction of 117 species

Effects of a Severe Freeze on Native Woody Plants in the Lower Rio Grande Valley, Texas

The effects of a severe freeze in December, 1983 on the native plants of the lower Rio Grande Valley, Texas were determined for 75 species. Damage was initially assessed by examining leaves, apical meristems, and cambial tissues of stems. Initial assessments were confirmed by surveys in the spring when new leaves were present. Forty-three species were either undamaged or had only minor leaf damage. Twenty-two species with damaged leaves had intact apical meristems or showed evidence of damage for less than 10 cm below the apical meristem. Three species, Leucaena pulverulenta, Cordia boissieri, and Karwinskia humboldtiana, had more extensive damage, i.e., 10 cm - 40 cm below the apex, but showed evidence of recovery by the presence of undamaged cambial and phloem tissues below the apex. Eight species, Avicennia germinans, Capsicum annuum var. glabriusculum, Cereus pentagonus, Chiococca alba, Citharexylum berlandieri, Erythrina herbacea, Iresine palmeri (male plants), and Petiveria alliacea, were seriously damaged. Temperatures lower than those occurring in December, 1983, or similar temperatures for much longer periods of time, would be necessary to kill most of the native species in the lower Rio Grande Valley, Texas

Comparison of the Effects of the Severe Freezes of 1983 and 1989 on Native Woody Plants in the Lower Rio Grande Valley, Texas

Freeze damage to native woody plants was assessed at the same four sites in the lower Rio Grande Valley, Texas, in 1983 and 1989. The number of severely damaged species was greater in 1989 possibly because temperatures in 1989 were lower and longer in duration below freezing versus 1983. Thirty0five species (48.6%) had the same damage index value for the two freezes, and 24 (33.3%) species showed no damage in either year. More than half of the 72 species analyzed (55.5% in 1983 and 51.3% in 1989) showed no damage or only leaf damage, indicating most of the native woody species are well adapted to survive periodic freezes. In 1989, Avicennia germinans, Cordia boissieri, Leucaena pulverulenta, Karwinskia humboldtiana, and Pithecellobium pallens included individuals killed to their bases. Heights of some of the L. pulverulenta exceeded 10 m. All species showed evidence of recovery by spring 1990

Annotated Checklist of the Flowering Plants of South Padre Island, Texas

This study catalogues the flowering plants of South Padre Island, Texas. A total of 207 species in 47 families is listed. The abundance and ecological distribution of each taxon are noted. Comparisons are made with the flora of Mustang Island, Texas. Ninety-three species, 96 genera and 36 families are common to both islands. Three families, Compositae, Gramineae and Leguminosae, contain large shares of the total number of species on both islands. Apparently, much of the floral diversity is due to the presence of a large number of species that are represented by small populations