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Working Ranch April/May 2016

pasture management BY LORETTA SORENSEN “I’ve spent much of my career in the intermountain west,” Thompson says. “Soil types vary here with a range of coarse grain, sandy and clay type soil often found along this area’s streams. Woody species like willow, alder and cottonwood are common in intermountain riparian areas. Woody vegetation creates the ribbons of green commonly seen along streams and rivers in the west’s arid areas. In areas like the Colorado River along I-70, some of the trees are over 100 years old. Even though the stream channel has moved away from where the trees originally sprouted, the roots still go down far enough that they reach the water table.” Where woody species thrive, stream and river gradients are fairly steep, having been eroded and reshaped by major fl ood events over decades. Seeds in this type of area are deposited by high fl ow and often germinate in or near pools of fl oodwater pushed past stream and river banks. The large and expansive tree roots of woody riparian species help stabilize the bank by reaching deeply into the soil for moisture. Over time, repeated fl ood events and the natural movement of streams cause stream channels to migrate so trees once growing adjacent to a river or stream continue to thrive in a radius around the water. New growth of woody species occurs closer to the stream, providing important bank stabilization for stream/river recovery following a major fl ood. “One of the concerns in the intermountain west is the invasion of tamarisk (salt cedar), an aggressive woody species that can degrade the quality of a riparian area,” Thompson continues. “The concern is that this plant doesn’t provide the same degree of bank stabilization as native riparian species. Tamarisk also doesn’t provide the same quality habitat for native birds and insects that willow, alder and cottonwood do.” The genus Tamarix is composed of about 50–60 species of fl owering plants in the family Tamaricaceae, native to drier areas of Eurasia and Africa. With its pinkish-red fl owers and feathery leaves, Tamarisk was fi rst imported to the U.S. as an ornamental. The plant’s fi brous roots do provide some erosion control, but not as much as native riparian species. However, it aggressively takes over areas with an extensive root system which can grow as much as 100 feet long. Cavity nesting birds are especially at risk in areas where tamarisk has displaced native riparian trees. Some 85 American bird species nest in cavities in dead or deteriorating trees or in healthy softer wood trees such as cottonwoods. Loss of trees for nesting has a negative effect on breeding success and many of the cavity nesting birds play an important role in controlling destructive forest insects. “Because tamarisk causes soil in areas where it grows to become more saline, it’s diffi cult for native woody species to compete with tamarisk once it becomes established,” Thompson explains. “Because tamarisk doesn’t provide the same quality of habitat for native birds and insects that thrive around cottonwoods, alder and willow, the riparian ecosystem changes, Evaluating riparian area health can be so complex that Colorado’s Bureau of Land Management (BLM) Fisheries/Riparian Program Lead, Jay Thompson, works with a team of specialists each time he takes part in riparian area assessment. Assessment teams look at hydrology, soil and vegetation as part of their riparian zone evaluation. Features including soil type, stream gradient and elevation infl uence the vegetation fl ourishing there. Editor: A thoughtful continuation of last issue’s Riparian Area article by our Pasture Management columnist Interdisciplinary team prepares to conduct a riparian assessment of Black Sulphur Creek near Meeker, Colorado. JAY THOMPSON 32 I WORKING RANCH I APRIL / MAY 2016


Working Ranch April/May 2016
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