Physiognomy and Structure: This vegetation is typically a sparse to dense grassland. Scattered forbs, shrubs, and young trees may be present but are not abundant.

Floristics: This coastal Pacific Northwest grassland alliance is dominated by non-native perennial, invasive species such as Anthoxanthum odoratum and Holcus lanatus, along with a mix of other non-native species.

Dynamics:  Stands of Holcus lanatus and Anthoxanthum odoratum are similar to those of Agrostis stolonifera and Schedonorus arundinaceus; however, the latter species occur in wetter and more brackish sites of managed wetlands (Pickart 2006). Both Holcus lanatus and Anthoxanthum odoratum occur along coastal terraces and moist pastures in central and northern California. Both plants particularly invade stands of the Calamagrostis nutkaensis, Carex obnupta, Danthonia californica, Deschampsia cespitosa, and Hordeum brachyantherum alliances (Heady et al. 1977, Keeler-Wolf et al. 2004, CNPS 2005, Ford and Hayes 2007).

Holcus lanatus is a recent invader, now dominating many coastal prairies of California. It has a high capacity for rapid vegetative growth in open areas, but it has a disadvantage against taller natives that create shaded conditions (Grime 1979). Stands of Calamagrostis nutkaensis and Festuca rubra are less resistant to Holcus lanatus invasion. Their canopy height inhibits light and reduces the ability of Holcus lanatus seedlings and flowering culms to invade dense stands; however, stands of Bromus carinatus are resistant because higher light is available (Thomsen and D''Antonio 2007). In addition, disturbed areas and Nassella pulchra stands are at risk for invasion because Holcus lanatus rapidly invade open sites with greater shoot biomass production (Thomsen et al. 2006).

Holcus lanatus stands contain species of conservation value, especially perennial grasses. Holcus lanatus is able to use summer moisture inputs from fog, which appears to alleviate water stress and thereby extend its growing season, increasing its persistence. Its invasion threatens the remnant patches of coastal prairie, which have been resistant to invasion by non-native annuals (Corbin et al. 2005). Cattle and elk grazing may be effective in reducing the abundance and spread of Holcus lanatus (Elliott and Wehausen 1974, Foin and Hektner 1986, Hayes and Holl 2003, Johnson and Cushman 2007). Without fire, grazing, or other forms of clearing, native shrubs such as Baccharis pilularis, Frangula californica, and Rubus ursinus and trees such as Pinus muricata and Pseudotsuga menziesii establish in these grasslands.