Variation in the Initial Success of Seeded Native Bunchgrasses in the Rangeland Foothills of Yolo County, California

Abstract

Investigations into the causes of variation in native bunchgrass distributions in California are constrained by the rarity of extant populations, their highly invaded nature, and their diverse and often unknown historical backgrounds. In addition, the correlates of success in California grassland restoration projects are rarely monitored. While controlling for seeding densities, we investigated correlates of establishment success for a mix of native bunchgrasses seeded into a non-native annual grassland with a history of agriculture and grazing in Yolo County, California. Six native grass species— blue wildrye (Elymus glaucus), big squirreltail (Elymus multisetus), Idaho fescue (Festuca idahoensis), California melicgrass (Melica californica), purple needlegrass (Nassella pulchra), and Sandberg bluegrass (Poa secunda)—were drill seeded in the fall of 1999. In order to minimize recruitment of non-native annual grass seed, the land was prepared with a spring burn and fall application of glyphosate prior to seeding. Through the third growing season, the cover of planted native grasses was significantly greater on north-facing slopes than on slopes with southern aspects. This was likely due to more mesic conditions on such sites rather than reduced competition with non-native plants. In the first growing season, distinct dense patches of filaree (Erodium botrys) became apparent. Native bunchgrasses overall, non-native grasses, and nonnative forbs all had significantly less cover inside these patches of filaree. Purple needlegrass was an exception to both of these trends, being insensitive to both aspect and filaree patches. These results reinforce the reputation of purple needlegrass as a species with wide ecological tolerance and excellent restoration potential.