Flood disturbance and riparian species diversity on the Colorado River Delta

Abstract

Abstract. We investigated the influence of channel migration and expansion on riparian plant species diversity along the lower Colorado River near the United States-Mexico border. Using repeat aerial photography in a GIS we identified and classed areas of low, moderate, and high disturbance frequency caused by channel expansion and migration. Replicate vegetation plots (12 m  12 m) were sampled in each of the three disturbance classes. One-way ANOVA was used to test for differences in species richness, species diversity (using the Shannon-Weiner Index) and overall percent ground cover of plants between the three disturbance classes. Regardless of disturbance class, plots were dominated by trees or shrubs, especially the non-native Tamarix ramosissima, as well as Pluchea sericea, Baccharis salicifolia and Salix goodingii. Clearly woody species constitute the great bulk of overall species richness, percent ground cover, and species diversity (H 0 ) in each disturbance group. No overall statistically significant differences were revealed among the disturbance groups for values of species richness, percent ground cover, or the Shannon-Wiener Index, though paired contrasts of means revealed that total percent ground cover on low disturbance plots was significantly higher than on moderately disturbed plots. Spatial and temporal variability in riparian diversity in the study area appears to hinge on factors other than disturbance frequency such as salt or drought stress. Alternately, our results could be interpreted as suggesting that in the presence of intensive flow regulation, disturbance plays a secondary role to ecological stresses, similar to that demonstrated by others. Intentional flood pulses are advocated as a restorative management strategy for improving plant productivity, management of exotic species (particularly T. ramosissima), and restoration of overall biodiversity.

Reptiles

“…For example, Cunha et al (1985) mentioned 77 species for the Carajas region, Pará, in the Brazilian Amazonia, and Dsuelmann (1978) registered 91 reptile species in the Ecuadorian Amazonia. This would be explained by the following factors: (1) Riparian ecosystems are between the most diverse, dynamic, and complex biophysical habitats of the world's surface (Tiegs et al 2005). Flood pulses generate a wide spatiotemporal heterogeneity of habitats and resources, which can be used by terrestrial and aquatic species, increasing considerably plant and animal richness in the system (Junk et al 1989).…”

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

“…Nevertheless, quantifying fluid force is very difficult because the relationship between tree height and water depth changes (Tanaka et al 2006). Many researchers have conducted experiments and/or field investigations on the effects of flooding on floodplain trees (Yamamoto and Kozlowski 1987;Terazawa et al 1992;Terazawa and Kikuzawa 1994;Yamamoto et al 1995;Watanabe et al 1996;Friedman and Auble 1999;Azami et al 2004;Capon 2005;Tiegs et al 2005;Asaeda et al 2009a, b;Tanaka and Yagisawa 2009).…”

Spatial and temporal tree colonization in a midstream sediment bar and the mechanisms governing tree mortality during a flood event

“…Azami et al (2004) observed that downstream river channels became forested subsequent to dam construction. Changes in floodplain inundation can lead to an increase in floral diversity (Tiegs et al, 2005;Stromberg et al, 2007) or a decrease (Van Oorschot et al, 1998).…”