Biology Reference
In-Depth Information
Fig. 7.4
Examples of sites in different stages of
B
.
tectorum
invasion in Great Basin sagebrush
steppe. Left panel = first state where A.
tridentata
shrubland has understory of native perennial
grasses and minimal invasion. Center panel = transitional site with A.
tridentata
canopy but under-
story of
B
.
tectorum
. Right panel = state where shrubland has been fully converted to B.
tectorum
dominance (photographs: courtesy of Bob Blank, USDA-ARS, Reno Nevada)
Management objectives include increasing native grasses and forbs through com-
petitive release from shrubs and trees, and reducing woody fuel loads to minimize
the risk of high-severity fires. Treatments target
A. tridentata
or pinyon and juniper
trees and may include prescribed fire or application of the herbicide tebuthiuron
(Monson et al. 2004). A separate objective may be to rejuvenate shrub stands char-
acterized by old age individuals and a lack of seedling recruitment. In this case,
treatment often involves brush beating or mowing of
A. tridentata
to decrease shrub
density, promote shrub seedling recruitment, and increase native herbaceous spe-
cies through competitive release (Monson et al. 2004). Ideally, areas selected for
these treatments have sufficient native perennial herbaceous species that reseeding
is not required.
In the next state which we refer to as
transitional
, the community has low resil-
ience and is at risk of crossing a biotic threshold following fire or other disturbance
that could result in a new ecological state dominated by
B. tectorum
. Herbaceous
perennials may be distributed throughout the community, but are present in rela-
tively low percentages. Native shrubs are a significant part of the community, but
B. tectorum
is present and moderately abundant (Fig. 7.4, center). Management
objectives are to decrease woody fuel loads, rejuvenate
A. tridentata
stands, and
