Biology Reference
In-Depth Information
when temperature is not a factor. High variability in available soil water at lower
elevations may result in lower average native perennial cover and increased win-
dows of opportunity for growth and reproduction of
B. tectorum
when available soil
water is above a certain level (Chambers et al. 2007).
7.3.5 Current Management Approaches
The type of management approach or restoration activity used depends on the stage
of invasion and the environmental characteristics of the affected communities (see
Whisenant 1999; Chambers 2005; D'Antonio and Chambers 2006). Site prioritiza-
tion depends on management goals and the need to maintain or improve habitat for
a growing number of animal species obligate to sagebrush ecosystems, such as sage
grouse (
Centrocerus urophasianus
) (Hemstrom et al. 2002). For the purposes of
discussing management approaches for areas exhibiting
B. tectorum
invasion, we
describe three ecological states (Figs. 7.3 and 7.4). In the first state, resilience is
high for most
Artemisia
community types. The existing vegetation is managed to
maintain or increase resilience to disturbance and resistance to
B. tectorum
inva-
sion. Shrubs or trees may be increasing in abundance, but native herbaceous peren-
nials are still a significant component of the community.
B. tectorum
may be
present, but has relatively low abundance. Preventative management can be used to
increase resistance by reintroducing disturbance in the form of fire or fire surrogate
treatments (Wright and Chambers 2002; Chambers 2005; Miller et al. 2005).
Fire
Woodland or Shrubland
Understory intact
B. tectorum
P/A
Native Grasses &
Forbs
B. tectorum
P/A
State 1
No Fire
Overgrazing
No Fire
Overgrazing
Herbicide
Mechanical
Threshold
Woodland or Shrubland
Depleted understory
B. tectorum
abundant
State 2
Fire
B. tectorum
Dominant
State 3
Fig. 7.3
State and transition model for Great Basin sagebrush steppe in western USA. Boxes
represent ecosystem states. P/A indicates present or absent but not abundant. Arrows represent
processes promoting transitions among states
