Biology Reference
In-Depth Information
The project seeks to increase seed supplies of native plant species, particularly
forbs. Its components include plant selection (source-identified seed sources, meth-
ods of propagation), seed and seeding technology, and seed production (federal and
state nurseries, NRCS, private growers).
Sagebrush ecosystems are changing at a rapid rate. The 2005, 2006, and 2007
fire seasons had among the largest areas burned on record with 437,060, 542,683,
and 360,170 ha (1,080,000, 1,341,000, and 890,000 acres), respectively, burned in
the state of Nevada alone (http://www.forestry.nv.gov/docs/2007_accomplish-
ment_report.pdf). A high percentage of sagebrush communities that burned will be
invaded by or converted to
B. tectorum
(Hemstrom et al. 2002). It has been sug-
gested that managers use a triage process involving “sorting through the sagebrush
communities to allocate resources to maximize the number, size, type, and distribu-
tion of communities that survive” (Wisdom et al. 2005). The process includes
(1) determining which communities are resilient and which are not, i.e., determin-
ing their ecological state, (2)developing a systematic process of prioritizing sites,
across the entire region, for management activities, (3) utilizing appropriate man-
agement techniques to maintain sagebrush communities with a high degree of
resilience, and (4) restoring some transitional or converted communities to serve
goals of enhancing intact communities that will be resistant to
B. tectorum
invasion.
7.4 ConcludingThoughts
The two examples discussed here provide alternative views on how to promote
native species in the face of grass invasions. In both cases the invaders are wide-
spread and persistent, but managers are exploring ways to promote native species
by focusing on maintaining or restoring resilience to the native assemblage, or
establishing resistant plant assemblages that will reduce the intensity of reinvasion.
The Hawaiian example is unusual in that it advocates promotion of a different type
of plant community than is known to have existed on the invaded sites - a form of
rehabilitation. Such an approach may be the only means for promoting more desir-
able species in the face of persistent, disturbance-promoting invaders where the
new disturbance, fire, is not part of the historical successional framework of the
sites and has resulted in an alternative persistent state. In the Great Basin, by con-
trast, fire was part of the preinvasion (pre-European) disturbance regime and suc-
cessional framework (Fig. 7.3) and if perennial herbaceous species are still present
in the native community, it is often possible to restore resilience and resistance prior
to degradation by the invader. In the Great Basin, native grasses and forbs that
respond favorably to increased resources following disturbance or management
treatments can decrease invasion by
B. tectorum
and, thus, it is also possible to
promote resistance. However, in both case studies the supply of native seed for
enhancing resistance or resilience (or both) is an important factor limiting manage-
ment options. The concepts of resistance and resilience are fundamental ecological
