Biology Reference
In-Depth Information
than intact native communities (Chambers et al. 2007). The IFAFS project com-
pared the performance of almost 20 native grass and forb species and two
Agropyron
accessions (Nowak et al. 2006). One accession,
A. desertorum
“CD II,” outper-
formed native grasses in 30% of comparisons, while the other (
A. desertorum
“Valvilov”) did not perform better. Several native accessions performed well at
multiple locations, are commercially available, and provide viable alternatives to
introduced species.
An approach for building community resistance is active seeding of functionally
diverse species that will maximize resource uptake by the entire community once
established. Revegetation mixtures that include grasses, forbs, and shrubs with var-
ying life forms and rooting depths should facilitate resource extraction through the
soil profile, while species with different phenologies should maximize use of avail-
able soil resources throughout the growing season. Thus, resistance would be maxi-
mized both in the short and longer terms.
The challenges of integrating these approaches are illustrated by the IFAFS
project. It evaluated the effectiveness of control of
B. tectorum
using glyphosate, a
short-lived herbicide, to reduce population abundance, followed by immobilization
of soil nitrogen through sugar (sucrose) applications (Nowak et al. 2006) simultane-
ous with seeding a diverse mix of native grasses, forbs, and shrubs. Although
sucrose addition decreased available N and initial
B. tectorum
biomass and seed
production, by the second growing season the effect had disappeared (Mazzola
et al. 2008). Sucrose addition also reduced growth of native plants and may have
resulted in increased overwinter mortality of seeded natives (Mazzola 2008).
Competitive effects of the seeded native species on
B. tectorum
reinvasion were
slight although expected to increase as the native species mature. The native species
were seed limited relative to
B. tectorum
. Higher seeding rates (600 vs. 150 or 300
plants m
−2
) resulted in higher establishment of natives as long as
B. tectorum
densi-
ties were relatively low (<300-500 plants m
−2
) (Mazzola 2008).
Recreating sagebrush communities with the functional diversity necessary to
support sagebrush-obligate wildlife species and to resist
B. tectorum
invasion is
therefore a challenging management goal. Although establishment of several native
grass accessions was relatively high in the IFAFS project, establishment of native
forbs and shrubs was low and seed availability was limited. For systems dominated
by
B. tectorum
, it may be possible first to seed with competitive native grass accessions
and then seed with a more diverse species mixture. Although native grasses with broad
amplitudes are commercially available, the volume of seed needed to reseed burned
areas at a reasonable rate is very high. Native species are generally seed limited
relative to
B. tectorum
, and typical seeding rates for native species are probably
inadequate (Mazzola 2008). Also seed increase programs and seed zones for native
forb and shrub species are just beginning to be developed and for most species, seed
supplies are far too limited for large-scale restoration efforts. These limitations are
being addressed, in part, by the Great Basin Native Plant Selection and Increase
Project, a collaborative effort of the BLM, Great Basin Restoration Initiative US
Forest Service, Grasslands, Shrublands and Deserts Project, and other regional agencies
and universities (http://www.fs.fed.us/rm/boise/research/shrub/greatbasin.shtml).
