Plants

Historic Landscape
The mission's landscape has changed dramatically over the past 200 years and continues to evolve in response to shifting hydrological and climate conditions. The introduction of grazing, agriculture, and irrigation to the site in the 19th century disrupted original plant communities. Around the mission site and visitor center, the NPS addition of mown lawns, ornamental trees, and other cultivated landscape features continues to impact the historic plant cover.

It is probable that at the time the mission was established, a mixture of three plant communities occupied the site: a narrow plant community consisting of dense tangled thickets of willows, cottonwoods, wild dogwoods, blackberries, elderberries, and other species common to riparian areas probably occurred in the floodplains along the Walla Walla River and nearby Mill Creek; an association of perennial grasses, shrubs, and native forbs occurred on the hillsides where soil depths and drainage were greater; perennial grasses common to the Palouse dominated the rest of the mission site.

Whitman Mission NHS has been engaged in substantial revegetation efforts over the past 30 years to reduce managed turf, noxious weeds, and other introduced species. Threats from invasive plants continue to occur despite efforts to reduce their impact, several species after still highly invasive and detrimental to the pre-white settlers landscape.

Invasive Species

In 1997, an inventory of exotic pest plant species identified the following six species of concern: field bindweed (Convolvulus arvensis), jointed goatgrass (Aegilops cylindrica), poison hemlock, (Conium maculatum), yellow starthistle (Centaurea solstitalis), Canada thistle (Cirsium arvense), and Scotch thistle (Onopordum acanthium). Teasel, is another exotic. Teasel is a non-native plant whose spiky, dried flower heads were used to comb wool before spinning. Each of these plants can dominate native grasses and plants when left unchecked and present significant issues for resource management at Whitman Mission.

Sources:

Whitman Mission National Historic Site: General Management Plan, September 2000. U.S. Department of the Interior, National Park Service.

Marcus and Narcissa Whitman and the Opening of Old Oregon. Clifford M. Drury.1986. Northwest Interpretive Association, Seattle, Washington.