Western PNW Grasslands

West of the Cascades, Pacific Northwest grasslands provide both a continuation of our work in California grasslands as well as a counterpoint to the rapid historic transition of southern grasslands to annual dominance in the 1800s. This transition, “one of the best known examples of large-scale community change occurring in North America over the past two centuries”, was precipitated by the novel agricultural disturbance imposed by colonial settlers. California’s hot, dry summers created an ideal home for Mediterranean annual grasses pre-adapted to such conditions. While nonnative perennial pasture grasses have invaded western Oregon and Washington’s grassland, this region has so far resisted the more fundamental and dramatic state-change to annual dominance.

The PNW mean annual temperature is expected to increase by 2.7 to 6°C by 2100 due to anthropogenically induced climate change. As the PNW’s climate becomes more similar to California’s, there is potential for a widespread change from perennial to annual grass dominance. For example, researchers at the University of Oregon demonstrated widespread perennial die-off and annual grass invasion in a warming experiment across a latitudinal gradient in the PNW. A “Californication” of PNW grasslands would bring a number potential changes, including increased fire frequency, soil carbon loss, an increase in noxious weeds, increased erosion, a shortened forage season, and reduced biodiversity.