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Riparian Ecosystem Creation and Restoration:
A Literature Summary

Case Studies

Lower Colorado River

Three well-documented case studies in the WCR Data Base (Table 3) further demonstrate techniques used for planning, implementing, and monitoring individual riparian ecosystem creation/restoration projects.

Lower Colorado River

One of the most well-documented case studies is Anderson, Ohmart, and associates' riparian revegetation study on the lower Colorado River on the border of Arizona and California (Table 3). A detailed historical account is presented in Ohmart et al. (1977), which documents the continued decline in cottonwood communities along the lower Colorado River. This type of analysis is helpful in providing impetus for management decisions relative to wetland creation/ restoration. Examining past conditions permits an evaluation of changes and a postulation of causes. Knowledge of the past also aids in formulating management plans for the future.

The first phase of the lower Colorado River study involved determination of vegetative parameters associated with large avian densities and diversities prior to restoration (Anderson et al. 1979). Birds were surveyed two or three times each month over a 2-year period. Communities were classified according to predominant vegetation and vertical structure. Differences in bird densities in 23 community types were documented by analysis of variance tests. A revegetation design was developed that maximized vertical and horizontal foliage diversity and included plant species of proven value to wildlife.

Revegetation efforts involved removal of the exotic salt cedar from a site and replanting this site and a nearly devoid dredge spoil site with native vegetation. Holes were angered for trees, and an irrigation system was installed to aid in plant establishment in this arid region. Three communities were superimposed on a single area. An early ephemeral stage was dominated by annuals of high wildlife value. Shrubs, the second stage, were planted to help offset early losses from clearing and to provide habitat diversity. The third stage of~planted trees (e.g., cottonwoods, willows) provided the dominant vegetation. As trees mature their full potential value to wildlife will be achieved and a new balance of shrubs and trees will develop.

During the second phase, monitoring of changes, not only in vegetation but also in birds, mammals, reptiles, and invertebrates began, and statistical comparisons were made with control (native) areas. Changes in vegetation composition, community structure, and vertebrate densities and use have been documented in various reports over the 5 years of monitoring (Anderson and Ohmart 1982, 1985; Anderson et al. 1984).

Growth and survival of planted trees have been well documented (Anderson and Ohmart 1982; Anderson et al. 1984). Soil and salinity data also were collected. Soil analysis included vertical and horizontal variation in soil distribution (Anderson and Ohmart 1982).

The lower Colorado River study exemplifies a well-planned effort to restore riparian habitat for wildlife. A historical evaluation and prerestoration surveys of vertebrates and vegetation provided baseline information to aid in the design of the creation/restoration effort. Changes in habitat and wildlife populations were carefully monitored and statistically tested, and results were published in numerous papers. The authors of these papers have stressed the need for careful site planning, development of diverse habitats, and continued monitoring of revegetation efforts. Anderson and Ohmart (1982) cautioned against using findings from a 2-year study to make predictions about growth and mortality of vegetation after 4 to 10 years. They stated that results should be considered preliminary until the site is at least 15-20 years old. Two years is not enough time from which to draw any conclusions beyond that time or beyond the range of variables studied.

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