104
ERDC TR-04-1
4.5
POPULATION PATTERNS OF PIONEER TREES
The presence of cohorts of adult pioneer riparian trees is almost always
evidence of past flooding on undammed rivers, since physical disturbance and
adequate moisture are requirements for initial seedling recruitment. However,
because such cohorts may have established in association with very large but
infrequent flood events (Friedman et al. 1996, Katz 2001, Friedman and Lee
2002), they may not be good indicators of the ordinary high water mark. For
example, on the Arikaree and South Fork Republican Rivers in eastern Colorado,
riparian forests are dominated by Populus deltoides and Salix amygdaloides
adults that established following the flood of record in 1935 but that occur on
geomorphic surfaces that have almost never been inundated since that year (Fig.
23) (Katz 2001). Similarly, large mature P. fremontii individuals occur on high
flood terraces on the Escalante River in Utah, even though such surfaces are
rarely inundated (Irvine and West 1979). Further, even if adult trees did become
established in association with an ordinary high flow that occurred several
decades previously, their locations may not accurately delineate the present
ordinary high water level. That is, channel migration, incision, floodplain aggra-
dation, or other geomorphic processes may change the spatial patterns of the
Figure 23. Mature Populus deltoides stand with a xeric understory on the
Arikaree River, Colorado.
Previous Page
