Ecological Characterization of a Riparian Corridor along the Río Conchos, Chihuahua, Mexico

Restoration of riparian areas is an important step toward improving water flow and water quality of the Rı́o Conchos in northern Mexico. To provide background data for restoration decisions we characterized the ecological integrity of a 40-km-long riparian corridor along the middle Rı́o Conchos. The characterization consisted of determining dominant species of trees and shrubs, structure, and quality of riparian habitat using standard transect sampling and a riparian habitat-quality index (QBR index) along the corridor. Our data indicate that willow (Salix nigra) and mesquite (Prosopis glandulosa) are the dominant trees in the riparian zone, and that although invasive saltcedar (Tamarisk ramosissima) populate nearby agricultural lands and irrigation canals, they have not yet invaded the riparian areas of the middle Rı́o Conchos. Habitat degradation is occurring; the major sources of negative impacts to riparian habitat are, in order, overgrazing, sewage input into the river, and gravel extraction from the river channel. RESUMEN—La restauración de áreas ribereñas es un paso importante para el mejoramiento del gasto y calidad del agua del rı́o Conchos, en el norte de México. Para obtener datos base para planes de restauración, caracterizamos la integridad ecológica de un segmento de 40 km de zona ribereña del medio rı́o Conchos. Esta caracterización consistió en la identificación de especies dominantes de árboles y arbustos, estructura, y calidad de hábitat utilizando métodos estándares de transectos ası́ como un ı́ndice de calidad de hábitat ribereño (QBR) a lo largo del rı́o. Los resultados indican que los árboles dominantes son sauz (Salix nigra) y mesquite (Prosopis grandulosa), y que aunque el árbol invasor cedro de sal (Tamarix ramosissima) está presente a lo largo de canales de irrigación y áreas de cultivo cercanas, no ha invadido todavı́a el área ribereña del medio rı́o Conchos. La zona ribereña presenta signos de degradación de hábitat especialmente por sobrepastoreo, descarga de aguas negras, y extracción de grava del lecho del rı́o, en orden de mayor a menor impacto. Vegetational vitality is essential for function and structure of ecosystems in riparian habitats (Naiman and Decamps, 1997). Although numerous studies on riparian habitats have been conducted for the parts of the Rı́o Grande Basin located within the United States, there are few for the parts of the basin extending into Mexico. In the United States, basins are threatened by various human disturbances such as groundwater decline (Stromberg et al., 1996), urban growth (United States Environmental Protection Agency, http:// www.epa.gov/earth1r6/6wq/usmexicoborder/ index.htm), and invasive species (Weeks et al., 1987; Howe and Knopf, 1991; H. Lujan, www. environmentaldefense.org/documents/4018_ LaInvasionDeTamarisk.pdf). The Rı́o Conchos is a major river in northern Mexico, its middle and lower portions flowing through the Chihuahuan Desert into the Rio Grande at the Mexico-United States border. Little is known about riparian vegetation along the river. However, reduction of water quality, diversion of surface water, overgrazing, depletion of groundwater, and introduction of non-native species in the past few decades have most likely impacted riparian habitat of the Rı́o Conchos (Comisión Nacional para el Conocimiento y Uso de la Biodiversidad, 2000). For example, it is estimated that one-half of native species of fishes within the basin are threatened with extinction (Hubbs, 1990) and aquatic species in general are being negatively affected by human activity (Edwards et al., 2001). The Southwestern Naturalist swna-53-01-13.3d 4/1/08 13:01:13 96 THE SOUTHWESTERN NATURALIST 53(1):96–100 MARCH 2008