Regeneration of Native Trees in the Presence of Invasive Saltcedar in the Colorado River Delta, Mexico

• Published in: Conservation biology Vol. 19; no. 6; pp. 1842 - 1852
• Main Authors: NAGLER, PAMELA L., HINOJOSA-HUERTA, OSVEL, GLENN, EDWARD P., GARCIA-HERNANDEZ, JAQUELINE, ROMO, REGGIE, CURTIS, CHARLES, HUETE, ALFREDO R., NELSON, STEPHEN G.
• Format: Journal Article
• Language: English
• Published: 350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK Blackwell Science Inc 01-12-2005; Blackwell Science; Blackwell; Blackwell Publishing Ltd
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Conservation; Conservation biology; Conservation, protection and management of environment and wildlife; especie invasora; fire; Fire scars; flood flows; Floodplains; Floods; flujo de inundación; Forest regeneration; Freshwater; fuego; Fundamental and applied biological sciences. Psychology; General aspects; Groundwater; humedales; invasive species; Native species; Nonnative species; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Plant populations; Populus; Populus fremontii; ribereño; riparian; River deltas; River water; Rivers; Salix; Salix gooddingii; Shrubs; Tamarix; Tamarix ramosissma; Trees; Vegetation; wetlands; Central America; Mexico; America; Colorado River; Mexico, Sonora; flood flows; Invasion; Salicaceae; Regeneration; wetlands; Tamaricaceae; Invasive species; Salix; Flood; Riparian; Dicotyledones; Angiospermae; Fire; Tree; Spermatophyta; Populus; Wetland; Native species; Environmental protection; Tamarix
• ISSN: 0888-8892; 1523-1739
• DOI: 10.1111/j.1523-1739.2005.00234.x

Many riparian zones in the Sonoran Desert have been altered by elimination of the normal flood regime; such changes to the flow regime have contributed to the spread of saltcedar ('Tamarix ramosissma Ledeb.), an exotic, salt-tolerant shrub. It has been proposed that reestablishment of a natural flow regime on these rivers might permit passive restoration of native trees, without the need for aggressive saltcedar clearing programs. We tested this proposition in the Colorado River delta in Mexico, which has received a series of large-volume water releases from U.S. dams over the past 20 years. We mapped the vegetation of the delta riparian corridor through ground and aerial surveys (1999-2002) and satellite imagery (1992-2002) and related vegetation changes to river flood flows and fire events. Although saltcedar is still the dominant plant in the delta, native cottonwood (Populus fremontii S. Wats.) and willow (Salix gooddingii C. Ball) trees have regenerated multiple times because of frequent flood releases from U.S. dams since 1981. Tree populations are young and dynamic (ages 5-10 years). The primary cause of tree mortality between floods is fire. Biomass in the floodplain, as measured by the normalized difference vegetation index on satellite images, responds positively even to low-volume (but long-duration) flood events. Our results support the hypothesis that restoration of a pulse flood regime will regenerate native riparian vegetation despite the presence of a dominant invasive species, but fire management will be necessary to allow mature tree stands to develop.