Sagebrush - Mountains and Plains: The Ecology of Wyoming Landscapes - page 123

a winter annual that begins growth in the fall or early
spring and gains a competitive edge over many native
species that are slower to initiate growth. Generally,
fire and heavy livestock grazing hasten the spread of
cheatgrass, though some research suggests that proper
management of native perennial species can slow this
invasion. 72 native species are more likely to become
established if actions are taken to favor such species
within a year or two of a fire, for example, by seeding
desired native species and protecting the rangeland
from excessive grazing. the maintenance of biological
soil crusts seems to be important as well (as discussed
later).
With cheatgrass as a component of the flora (or even
just in the seed bank), land managers are confronted
with the conundrum of increasing desired native
grasses by burning big sagebrush without increasing the
abundance of an undesired, introduced weed. 73 More-
over, cheatgrass can become so abundant that it greatly
increases the flammability of the vegetation. Fires then
occur more frequently, diminishing the chances of sage-
brush re-establishment and causing a decline in some
perennial grass species—favoring cheatgrass expansion
still further (fig. 7.13). 74 the economic impact of cheat-
grass is moderated to some degree by the fact that it can
be good forage before it flowers, but converting semi-
arid steppes to vegetation dominated by an introduced
annual is a significant change that has undesirable
consequences. in addition to increasing flammability,
cheatgrass is associated with an increase in soil temper-
ature and erosion, along with reductions in soil organic
matter and small mammal abundance and diversity. 75
the cheatgrass problem is not restricted to land man-
aged for livestock. For example, a fire burned a large stand
of big sagebrush in Little Bighorn Battlefield national
Monument in southern Montana, where livestock have
not grazed for many years. Much of the sagebrush was
killed, and bluebunch wheatgrass, a co-dominant before
the burn, became less abundant. cheatgrass became
more common on the burned area, as did yellow sal-
sify. Managing the vegetation of a national monu-
ment so that it reflects conditions prior to the arrival of
euroAmericans is a goal that sometimes seems impos-
sible once invasive species become established. Further
research is necessary to resolve perplexing ecological
problems such as this one.

300

Grasses

Thickspike
wheatgrass and
Plains reedgrass

200

Bluebunch
wheatgrass

Bluegrass

100

Idaho fescue Needle-and-thread

300

Shrubs

Horsebrush

Rabbitbrush

200

100

Sagebrush

1936 1942 1948 1954 1960 1966

YEAR

Fig. 7.12. changes in the canopy cover of several grasses and
shrubs after the burning of big sagebrush steppe in eastern
idaho. the burn occurred in 1937. An increase (or decrease)
in plant cover is indicated when the line for a species is above
(or below) the dashed line. the two shrubs that increased, rab-
bitbrush and horsebrush, are capable of sprouting from their
roots; big sagebrush declined, because it does not sprout, but
it eventually became re-established from seed. Adapted from
Harniss and Murray (1973).

efit, some becoming so abundant that they reduce the
growth of native species and the potential for restor-
ing wildlife habitat. cheatgrass ( Bromus tectorum ), also
known as downy brome, is the most notorious example.
this annual plant has greatly complicated the practice
of prescribed burning as a management tool. For many
years managers thought that cheatgrass would not grow
well at higher elevations, but it is now commonly found
throughout Wyoming, even at elevations above 7,000
feet. 68 With climate warming, it very likely will become
more common in some parts of the state. 69 other prob-
lematic species in shrublands include broad-leaved
pepperweed, canada thistle, Dyer's woad, halogeton,
leafy spurge, Russian knapweed, spotted knapweed,
Russian thistle, western salsify, and yellow and Dalma-
tian toadflax.70 70
cheatgrass was introduced to western north Amer-
ica in the late 1800s from the steppes of europe. 71 it has
become common in many areas, because the species is