Saltcedar is an invasive phreatophyte occupying riparian areas throughout the western United States. In New Mexico, saltcedar is a dominate plant along the Rio Grande, Pecos and Canadian Rivers and is particularly troublesome from the middle reaches of these rivers to the Gulf of Mexico. Saltcedar is an aggressive competitor often growing in near monoculture stands and is suspected of lowering water tables thus destroying wetlands and wildlife habitats.
Interspecies competition and shading by dense saltcedar results in reduced biodiversity. Saltcedar communities along the Pecos River have fewer indigenous plants compared to native plant communities where plant diversity and ground cover are greater. Saltcedar often colonizes the same open sites necessary for cottonwood regeneration, preventing cottonwood establishment. Saltcedar is able to exploit suitable sites over a longer period than native plants because of its season-long seed production.
In the Rio Grande River System, cottonwoods are present along the entire length of the river. However, cottonwoods are more numerous from Socorro upstream and below this point are localized among dense saltcedar thickets. Prior to saltcedar establishment, riparian communities downstream from Socorro were dominated by grasses such as alkali sacaton, inland saltgrass, screwbean mesquite, wolfberry, baccharis and coyote willow. The same is true most of the Pecos river system from Santa Rosa downstream. Historically, cottonwoods and willows located along the Pecos were mainly near areas with Artesian springs, near head waters and along some tributaries. Prior to saltcedar invasion, water quality was the limiting factor for cottonwood and willow establishment.
Saltcedar infested areas in New Mexico usually have low vertebrate densities and diversities compared to native plant habitats. Several studies report that saltcedar stands have fewer small mammals and birds compared to native riparian communities. The same is true for reptiles and amphibians. Bird species richness and number is lower in saltcedar areas along the Rio Grande but greater along the middle Pecos River. Apparently saltcedar can act as an ecological equivalent to other plants for some breeding bird species. Birds will apparently use saltcedar differently in various locations, depending on the species and its biological habits.
The banks of the middle and lower portion of the Pecos River were historically dominated by saltgrass and other herbaceous communities rather than by taller woody vegetation. This is in contrast to most other perennial riparian systems throughout the west where trees and shrubs dominate. The increased presence of riparian-dependent birds within the Pecos River Valley can partially be attributed to the spread of saltcedar. Areas without saltcedar along the Pecos River are dominated by birds typical of a short grass prairie and are low in relative abundance and species richness. In areas of dense saltcedar, birds that prefer woodlands and grasslands are common.
Small mammal species richness in the middle Pecos River system is not different among vegetative communities consisting of dense saltcedar, open saltcedar, grasslands or mixed shrub grasslands. However, small mammals have a higher relative abundance in dense saltcedar relative to native areas. Total species richness of herptofauna is greater in native communities than in dense saltcedar along the Pecos River. However, relative abundance of herptofauna species is not different. These results suggest reptiles and amphibians would benefit from saltcedar reduction and management.
Over the last 75-100 years, saltcedar has altered the hydrology and plant succession of many western river systems. Unless restoration practices are implemented to manage saltcedar and to enhance regeneration of native species, diversity of flora and fauna along these rivers will continue to diminish.
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