Establishing Native Forbs within Existing Stands of Native Perennial Grasses from Transplants and Seed on Rural Roadsides in the Sacramento Valley of California

Robert L. Bugg and Cynthia S. Brown

Presentation at 49th Annual Meeting of the American Institute of Biological Sciences, August 2-6, 1998, Baltimore, Maryland. 1998

Conventional management of county roads in California includes regular disturbance by herbicides, mowing, and blading. These practices promote ruderal, usually non-native, species. Previous experiments have evaluated establishment and persistence of seeded native perennial grasses in rural rights-of-way (see: Bugg, R.L., C.S. Brown, and J.H. Anderson. 1997. Restoring native perennial grasses to rural roadsides in the Sacramento Valley of California: establishment and evaluation. Restoration Ecology 5:214-228.). In the present two experiments, we tested establishment efficiency for native forbs (non-grass herbaceous plants) amid pre-existing stands of native perennial bunchgrasses or tilled, bare ground controls.

In the first experiment, a mixture of forbs was seeded into two levels of background vegetation: established perennial native bunchgrasses vs. tilled, bare ground. Arroyo lupin (Lupinus succulentus), California poppy (Eschscholzia californica), chick lupin (Lupinus microcarpus), and Spanish clover (Lotus purshianus) established well when seeded into tilled, bare ground, but the annual tansy phacelia (Phacelia tanacetifolia) and the perennials narrow-leaf milkweed (Asclepias fascicularis) and blue-eyed grass (Sisyrinchium bellum) did not. None of the forbs tested established well by direct seeding into pre-existing stands of native perennial bunchgrasses: canopy cover by forbs was significantly less in plots under the latter regime than in those with tilled, bare ground.

In the second experiment, two perennial forbs, warm-season active narrow-leaf milkweed and cool-season active blue-eyed-grass were grown in the greenhouse and outdoors in containers and later transplanted to the field. Container size, excavation method, and background vegetational regimes were varied. Small containers had volume 36 ml, depth 7.5 cm, and interior diameter at top 3 cm. Large containers had volume 105 ml, depth 13.6 cm, and interior diameter at top 3.6 cm. Excavation was by either dibble (impression) or corer (which removed soil from the hole). Transplants were inserted amid either tilled, bare soil or established perennial native bunchgrass stands.

Transplants inserted within plots of established native perennial bunchgrasses did not show significantly reduced vigor compared to those placed in tilled plots, but there was limited replication for this factor and thus little statistical power to detect such an effect.

Narrow-leaf milkweed performed better when grown in larger containers: its rapid growth phase begins late in the spring when rainfall is minimal and continues into the hot, dry summer, so transplants with deeper roots at the time of planting may have a resource acquisition advantage. By contrast, blue-eyed-grass did equally well when grown in either small or large containers: since its growing season is during the moist winter and spring, there probably was no advantage in having deeper roots at the time of transplanting.

Excavation technique did not affect narrow-leaf milkweed vigor, but blue-eyed-grass was more vigorous when excavation was by corer than when a dibble was used. We speculate that this may be due to the montmorillonitic clay soils, which swell and shrink in wetting and drying cycles, relieving compaction. The dibble method causes soil compaction, which may have interfered with growth of the cool-season perennial blue-eyed-grass, but compaction may have been reversed by the time narrow-leaf milkweed began rapid root growth in mid-spring.

Small containers and the dibble method present greater efficiencies of space and time for production and transplanting, so more detailed data and economic comparisons will be needed to assess trade-offs for establishing various forb species.

For more information: Cynthia Brown, Department of Agronomy and Range Science, University of California, Davis, CA 95616; csbrown@ucdavis.edu

DEC.596 Contributed by Robert Bugg