Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Abstract

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m2 experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m2), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m2) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.

Restoring resources for an endangered butterfly

“…presence of non-indigenous species vs. highly polluted soils) and techniques tested at one site for one set of problems may not generalize to other situations, even in attempts to restore the same habitat type. Experiments that investigate processes to recreate habitats are useful in designing restoration projects because they provide a mechanism to generalize techniques to a range of situations (Carlsen, Menke & Pavlik 2000).…”

Environmental Report 2005

“…The native perennial grass Poa secunda is most abundant in plots that are burned annually. Previous research shows that large-flowered fiddleneck is more successful in plots dominated by P. secunda compared to plots dominated by exotic annual grasses (Carlsen et al 2000), but early results from the fire frequency experiment show that large-flowered fiddleneck is more abundant in the unburned control plots dominated by dense annual grasses than in the burned plots. Data from plots burned at an intermediate frequency are not yet available.…”

Rare Plant Restoration and Monitoring at Lawrence Livermore National Laboratory, Site 300, Project Progress Report, Fiscal Year 2005 and 2006.

“…We know that Amsinckia grandiflora has been negatively impacted by the conversion of its habitat from native perennial grasslands to exotic annual grasslands (Pavlik et al, 1993;Carlsen et al, 2000). Controlled burns have been used at the Drop Tower experimental populations in an attempt to control exotic annual grassland and help to maintain a grassland habitat dominated by native perennial grasses, but several limitations to the use of controlled burns to establish native perennial grasslands as habitat for A. grandiflora have been identified.…”

“…Research on the Drop Tower experimental population and the Lougher Ridge experimental population, and data from management of the Drop Tower natural population indicate that competition from exotic annual grasses contributes to the decline of A. grandiflora, and that long term management to reduce exotic annual grass cover and restore and maintain the native perennial bunch grass community is necessary to ensure the persistence of this species (Pavlik et al, 1993;Pavlik, 1994;Carlsen et al, 2000). The USFWS and the U.S. Bureau of Reclamation have provided additional funding.…”

“…• 1999& 2000: On October 22 and 29, 1999, and on seven dates between October 20 and November 8, 2000, all areas of Site 300 were surveyed for flowering B. plumosa populations. Mapping included a combination of handmapping and GPS mapping (using a Trimple GPS unit).…”