Ecology and management of crested wheatgrass invasion

Crested wheatgrass (Agropyron cristatum Gaertn. [L.] sensu amplo), a perennial bunchgrass from the temperate steppes of Asia, was introduced to North America for livestock forage and land reclamation. Invasion by crested wheatgrass into adjacent native grasslands may impact biodiversity and ecosystem functioning, but documentation is lacking. Further, many land managers desire means to prevent invasion from economically valuable agricultural plantings and to restore invaded areas on lands set aside for biodiversity conservation.; A research program was designed to describe multiple scales of crested wheatgrass invasion patterns and impacts in mixed-grass prairie of Alberta and Saskatchewan, and to determine effective means for preventing invasion and restoring invaded grassland. Within the mixed-grass prairie region, crested wheatgrass invasion most commonly occurred on excellent condition rangeland and rarely on saline soils or poor condition rangelands. Among and within plant communities, invasion was associated with greater aboveground biomass and crested wheatgrass dominance, but lower species richness and vegetation diversity. Seedbank diversity was not different, but crested wheatgrass appeared to replace fringed sage (Artemisia frigida Willd.) as the most abundant species (40% of germinable seed), suggesting substantial seed inputs or seedbank persistence.; In field experiments, >90% of crested wheatgrass seed buried in the soil germinated or decomposed within 5 months. Conversely, >75% of seed elevated above the soil survived at least 26 months, suggesting seedbanks persist where sward management permits aerial seedbanks to form above the soil. Four years of repeated grazing, haying and glyphosate applications reduced or maintained low crested wheatgrass seedbank densities, but only glyphosate reduced adult plant cover. With the exception of glyphosate, no treatment significantly increased community diversity or similarity towards a native reference community. Selective glyphosate application allowed native species survival, and the flush of resource availability promoted native species germination from the seedbank and colonization from off-site. Restoration efficiency and effectiveness may be increased with a carefully sequenced combination of grazing to reduce crested wheatgrass seedbanks, then glyphosate to remove adult plants, then native grass seed additions to overcome dispersal barriers; particularly of those species competitively excluded by crested wheatgrass.