Potential Late-Holocene Disjunction ofSequoia sempervirenson the Central Oregon Coast

Abstract

A large (> 200-cm diameter) coast redwood (Sequoia sempervirens) stump occurring upright on an Oregon beach, 257 km from the northern limit of its native distribution, may be a remnant of an extinct disjunct population or it may be the result of vertical emplacement of a drift log. Holocene tree stumps in situ in paleosols commonly emerge on the shore platform as a result of a complex history of dune activity, subsidence, and erosion. An historical account reported organic soils associated with the stump during the late 1800s; such soils are normally removed quickly by wave action after exposure. We used several methods to corroborate this account. The stump’s in situ origin is supported by 1) a radiocarbon age indicating a death date between 1820 and 1720 years ago, coeval with other paleosols and in situ stumps; 2) its height and upright position, which are only matched by other in situ stumps; and 3) a photograph from 1912 showing uneroded wood inconsistent with a sea-drift history. Other evidence failed to support the in situ origin: 1) ground-penetrating radar did not reveal an associated paleosol, 2) the age of a nearby paleosols and stumps within 3 km were younger than the stump, and 3) three paleosols did not yield redwood pollen or wood. The only support for a sea-drift origin is that its age slightly predates a known tsunami that may have emplaced the stump. The balance of evidence suggests that the redwood stump is a remnant of an extinct late-Holocene disjunct population.