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40 I I I I I I I I I I I I I I I I I I I Historically the prairie grasses grew to the riverbank and cottonwoods were sparsely scattered along the Arkansas River except for the approximately 30-mile reach downstream of John Martin Dam that was known as the "Big Timbers," a rather dense grove of gigantic cottonwoods (7 to 8 feet in diameter) that grew on islands in the river and along the banks, and lacked a shrub understory (Vestal 1939; Grinnell 1923). Zebulon Pike first noted this stand on his journey up the Arkansas River in 1806. The Big Timbers was the only cottonwood stand of any appreciable size between Council Grove, Kansas, and the Rocky Mountains. The last of the large trees were gone by 1863, and the Arkansas Valley was virtually treeless for some period thereafter. Smaller, less spectacular cottonwood stands re-colonized the area such that, by the 1940s, they occupied about 40 acres per river-mile (Snyder and Miller 1991). Salt-cedar, a deciduous, needle-leaved tree, was introduced into the United States from Eurasia in the early 1800s (Robinson 1965). This species was first noted in the Arkansas Valley near Lamar in 1913 and had spread substantially by 1923 (Niedrach, cited in Lindauer and Ward 1968; Lindauer 1970). Local residents noted that salt-cedar spread extensively throughout the valley after the large floods of 1921 and 1937 (Lindauer and Ward 1968). Bittinger and Stringham (1963) found that woody phreatophyte sta~ds (primarily salt-cedar) increased by about 43% (or approximately 52 acres/year) from 1936 to 1957 in the floodplain between La Junta and Las Animas. By 1967, woody riparian cover in Bent and Prowers Counties occupied an average of 143 acres per river-mile, 93% of which was monotypic or mixed stands of salt- cedar (Lindauer and Ward 1968). Salt-cedar has become established in the understory of existing cottonwood galleries, however, more extensively, has replaced broad expanses of riparian grassland communities. Salt-cedar is a fast-growing species and is tolerant of saline soils, shallow groundwater, and poor water quality. It exudes a salty secretion which, when accumulated on the soil surface, suppresses other seeds from germinating. These properties give salt-cedar a competitive advantage over native riparian plants and enable it to form dense stands with low plant species diversity. While it provides wildlife with shrub cover, its food value is low. Salt-cedar provides lower quality wildlife habitat than native cottonwood-willow communities (Anderson et al. 1977, Engel-Wilson and Ohmart 1978, Hink and Ohmart 1984). Additionally, salt-cedar root systems are extensive and can reach a depth of 25 feet or more, contributing to relatively high transpiration rates. Conservative estimates indicate that dense stands can utilize 42 to 60 inches of water per year (Robinson 1952, Fletcher and Elmendorf 1955, Bittinger and Stringham 1963). The width of historic riparian communities along the Arkansas River is not well documented in accounts from the 1800s. George Bent noted that what remained of the "Big Timbers" stand in 1853 was only about two miles wide and five miles long (cited in Grinnell 1923). Currently within the three problem areas studied, the band of riparian vegetation varies from 250 to 3,000 feet wide. Although salt-cedar cQverage has increased dramatically, the overall areal extent of riparian vegetation has decre*sed over the past 100 years due to urban and agricultural development within the floodplain and the reduced effective discharge associated with irrigation diversion, off-river storage, and flood control storage in Pueblo Reservoir. Additionally, flood control operation has significantly reduced large flood events that formerly scoured extensi ve areas, creating suitable substrates for cottonwood and willow seed germination.