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~<.3 A typical riparian site along the river corridor conuins mountain alder, red~sier. several species of willow, sedge and rush, and horsetail. Coyote and Bebb are the most common species of willow. The narrow valley bottom and steep canyon sideslopes restrict riparian vegetation to the area adjacent to the stream channel. The riparian zone is typically three to ten feet wide; see Figure D. Alder, red-osier, and willow occupy a band adjacent to tbe active channel. Individual trees and small stands of narrowleaf cottonwood are scattered along the mainstem of the Piedra and along the tributaries near the mainstem; most are located on low terraces. Scbunatic Diqnm A.cti't'e Ch.aa.Del &.ad Riparia.a Zone -- Zoo< -- Zoo< Ao;In<e 0--1 QU Figure D Riparian species. especially willow. colonize deposition areas behind debris dams and gravel bars. Although the location of these areas will shift over time. the area occupied by riparian species within the wilderness probably remains relatively constant. There are two sites within the proposed wilderness area near the upper boundary where narrowleaf cottonwood is a major component of the plant community. At these sites, the valley bottom is wider and bas both tloodplains and low terraces which are occupied by cottonwood. Little regeneration of cottonwood was observed during a 1991 reconnaissance of the area. Based on the distribution of size classes at the sites near the upper wilderness boundary. regeneration appears to be episodic. Like other ~ottonwood species, successful regeneration of narrowleaf cottonwood requires a closely timed sequence of events. High flows must remove organic material and deposit or ex.pose a fresh layer of gravel sized and tiner sediments just prior to seed drop and the seedbed must remain moist during s~ling establishment Page 6