Invasion by Non‐Native Annual Grasses: The Importance of Species Biomass, Composition, and Time Among California Native Grasses of the Central Valley

Abstract

The Central Valley of California is noted for its dearth of remnant native grass populations and for low native grass seedling establishment within grasslands now dominated by non-native annual species. In contrast, remnant populations are common along the coast, and studies have shown an ability for seedlings and adults to compete with nonnative annual grasses. The invasibility of well-established populations of native grasses in the Central Valley remains unclear. The objectives of this study were to compare the invasibility of native grasses differing in density and species composition and, given the species in this study, to assess the ability of mixes with greater species richness to resist invasion relative to their abilities in monoculture. In the Sacramento Valley of California, six species of native grasses were planted at three densities in monospecific and mixed-species plots. Percent cover of native perennial and non-native annual grasses was measured in years 2 and 3, and biomass was sampled in year 5. Native grass biomass and, to a lesser extent, species composition were important in explaining variation in non-native grass invasibility in the fifth year. Species-rich treatments did not experience less invasion than would be expected by the proportional invasibility of each species in monoculture. However, invasibility of plots consisting of slower growing, shorter statured species decreased over time, suggesting a successional benefit to diverse communities. This study demonstrates that established stands of native grasses in the Sacramento Valley can resist invasion by non-native annual grasses and that stand biomass is a particularly important factor in determining invasibility.

Plant functional group identity and diversity determine biotic resistance to invasion by an exotic grass

“…; Mwangi et al . ), suggesting limiting similarity, whereas in other cases, different functional groups resist better (Lulow ; Sheley & James ), suggesting fitness inequality as one of the key resistance mechanism. MacDougall, Gilbert & Levine () propose that invasion success may depend on both fitness advantage and niche difference from resident species.…”

Short‐term priority over exotic annuals increases the initial density and longer‐term cover of native perennial grasses

“…While several California grassland studies have shown that established mature native perennial grasses can successfully compete with exotic annuals (e.g., Seabloom et al 2003, Corbin and D'Antonio 2004, Lulow 2006, recruitment of native perennial seedlings is rarely observed (Hamilton et al 1999, but see Seabloom et al 2003, Corbin and D'Antonio 2004). Indeed, the ability of a seedling to establish may be poorly correlated to the ability of an adult of the same species to survive and compete with neighbors in that same site (Peart 1989, Young et al 2005.…”

“…The continued dominance of exotic annual grasses in California's interior grasslands has commonly been attributed to their early germination and rapid growth relative to native perennial grasses (Bartolome and Gemmill 1981, Jackson and Roy 1986, Dyer et al 2000, Freckleton and Watkinson 2001, Rice and Dyer 2001, Harmon and Stamp 2002, Verdu and Traveset 2005, Lulow 2006, Lulow et al 2007; but see Clary 2008). Exotic annual grasses can emerge up to several days earlier than California native perennials (Reynolds et al 2001, Deering and Young 2006, Wainwright and Cleland 2013.…”

Using Remote Sensing to Evaluate the Influence of Grassland Restoration Activities on Ecosystem Forage Provisioning Services

“…However, without management intervention, mid-project gains were generally not maintained. Noxious weeds reestablished in all native seeded pastures in part because bunchgrass establishment and cover were lower than anticipated (Russell & Hartman 2005;Lulow et al 2007); higher density or higher biomass bunchgrass stands might be less prone to invasion (Lulow 2006;Thomsen & D'Antonio 2007 (Marty et al 2005). On the sheep ranch, where soils were generally shallower, native grass establishment was less successful and bunchgrasses were much smaller than those on deeper soils (Lulow et al 2007).…”