- Erigeron decumbens var. decumbens, known only from the Willamette Valley of western
Oregon, is listed as Endangered by the U.S. Fish and Wildlife Service and by the state of
Oregon. In 1993 a long-term population monitoring program for Erigeron decumbens
var. decumbens was initiated at Baskett Slough National Wildlife Refuge (Polk County).
The objectives were to assess long-term population trends, particularly patterns of
reproduction, recruitment, and mortality.
This report presents the results of the demographic monitoring from 1993-1999.
Considered together the following demographic parameters indicate that the measured
population at Baskett Butte (Baskett Slough National Wildlife Refuge) is declining.
1. The population size decreased every year but one with the 1999 population only
48% of the 1993 population.
2. Increasing mortality rates exceeded recruitment rates every year but one.
3. The percentage of the population that flowered generally decreased every year.
4. The average number of heads per flowering plant decreased each year beginning
in 1995 to 3.4 heads per flowering plant in 1999.
5. The pattern of average basal area per plant varied but the 1999 average basal area
is only 63% of that measured in 1993.
To stabilize the population, adaptive management strategies need to be developed
in conjunction with experimental approaches that will determine the factors responsible
for the population decline. A second approach to aid in the recovery of Erigeron
decumbens var. decumbens is to increase the population by transplanting cuttings or
plants grown from seed under greenhouse conditions or by sowing seeds in the field
under more controlled conditions. It is strongly recommended that future efforts to
stabilize the population at Baskett Slough National Wildlife Refuge be coordinated with
other agencies in the Valley who are also responsible for management of Erigeron
decumbens var. decumbens populations.
- Order No. 1448-13590-9-M047A
- Prepared for U.S. Fish and Wildlife Service Western Oregon NWR Complex.