Decline to Near Extinction of the Endangered Scotts Valley Polygonum Polygonum hickmanii (Polygonaceae) in Coastal Central California

Abstract

Scotts Valley polygonum Polygonum hickmanii (Polygonaceae) is a narrow endemic plant restricted to a specialized microhabitat (exposed bedrock in California prairie) in Santa Cruz County, California. The species was named in 1995 and subsequently listed as endangered under the U.S. Endangered Species Act and California Endangered Species Act in 2003 and 2005, respectively. Two occurrences exist on three properties in a recently urbanized area at the northern edge of the city of Scotts Valley, with a geographic range of 0.03 km². As of 2012 the species has declined to 128 plants on 61 m², having decreased from 604 plants in 2003, 1,612 plants in 1998 and 2,388 plants in 1997. In 2013 the primary threats to P. hickmanii are habitat alteration due to adjacent land uses and developments, and invasive plant species and accumulation of thatch. Cessation of grazing and fire suppression have likely contributed to the increasing presence of invasive plant species and accumulation of thatch. Intensive and adaptive management with monitoring will be necessary for P. hickmanii to survive. Unless management is implemented as a matter of urgency, the species will likely disappear within just a few years.