Riparian Landscapes - Mountains and Plains: The Ecology of Wyoming Landscapes - page 64

seedlings, enabling it to reproduce more rapidly than
cottonwood on the many streams in western states
where streamflow is regulated and floods are suppressed.
the fruits are commonly eaten and dispersed by birds.
Most reproduction is from seedling establishment,
though root sprouts do occur. invasion is hastened in
some areas because beaver preferentially cut and eat
cottonwood sprouts, thereby creating a more favorable
environment for Russian olive. And once established,
Russian olive better tolerates the aridity that develops
with drawdown of the water table. As is typical for
invasive plants, part of the exotic tree's success may
be attributable to the frequent preference of most
herbivores for native species. 43
the alluvial soils of riparian zones generally have
sufficient nitrogen for plant growth. nevertheless,
Russian olive has a symbiotic association with a
group of fungi known as Actinobacteria, which form
actinorhizae (analogous to mycorrhizae) that are capable
of nitrogen fixation. this adaptation may facilitate the
exotic tree's survival on the uplands, even though it
may not be critical on the floodplains. Various studies
have shown that the soil under Russian olives has
higher nitrogen levels than under cottonwood trees. 44
Some have wondered whether nitrogen enrichment of
the streamwater is higher because of the Russian olive,

and also whether such nutrient enrichment favors
the invasion of other exotic plants. Unusually high
proportions of the herbaceous plants in many riparian
zones consist of introduced species.
the other invasive plant, saltcedar, was introduced
to the region in the 1930s fig. 4.17; see also fig. 4.11). 45
it grows mostly at low elevations, such as in the Bighorn
Basin; the Wind River Basin; the lower parts of the
Green River, Powder River, and north Platte basins; and
northward into Montana. it has also been found above
7,000 feet in the Laramie Basin. With warming of the
climate, saltcedar could become more widespread, as it
tends be more drought tolerant than some native shrubs
and trees. 46 Both saltcedar and Russian olive grow
together on floodplains where the groundwater level is
dropping and upland plants are invading.
the seedlings of saltcedar tolerate saline soils better
than some native riparian species do. 47 this tolerance
can be attributed partially to salt-secreting glands on
the leaves. Salts released by the glands are deposited on
the soil from time to time by rainwater and also when
the leaves are shed. consequently, established plants
can elevate surface soil salinity through litterfall. 48
Saltcedar often grows so densely and uniformly over
large areas that few native species survive, and it does
not support wildlife as well as the native vegetation. Like

Fig. 4.17. Saltcedar is an introduced
invasive shrub in riparian landscapes
that is becoming more common at low
elevations in Wyoming and southern
Montana. Another invasive plant, hoary
cress, is visible in the foreground. Photo
by Brian Mealor.