THE POPULATION ECOLOGY OF A DUNE THISTLE, CIRSIUM RHOTHOPHILUM (ASTERACEAE)
Abstract
A population study of a thistle, Cirsium rhothophilum, was carried out in the coastal dunes of northern Santa Barbara County, California during 1978 and 1979. Seedling establishment, growth, flowering, and fruiting were observed in permanently marked transects. A total of 1,041 individuals were recorded. Despite 41% mortality during the year of study, the average population features changed remarkably little. Cirsium rhothophilum was found to be monocarpic but relatively long‐lived. Extrapolations from rosette size growth and proportions of rosettes in different size classes giving rise to flowering individuals suggest that the average plant may have a vegetative stage of more than 5 years. Growth analysis of c. rhothophilum is complicated by the subsurface branching of stems, presumed to be the result of insect damage and sand burial. Dissection of fruiting heads showed that sound achenes were only about 22% of the total number of potential achenes. Insect damage was evident on about 20% of the unsound achenes. Considering both the loss of achenes within heads and of entire heads which failed to mature, insects are estimated to destroy at least 25% of the achenes. Achenes germinate readily and do not appear to have more than mild dormancy. A burial experiment showed that emergence declined sharply with depth of burial to zero at 8 cm. Despite the dynamic nature of the dune habitat, C. rhothophilum populations appear stable. The relatively large size and ability to grow rapidly and adapt to burial allow C. rhothophilum to average out environmental vicissitudes.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Nov 01, 1983
- Source ID
- 10.1002/j.1537-2197.1983.tb10855.x
Entities
People
- Carla Scheidlinger
- Clayton R. Gautier
- Kathleen Guehlstorff
- Paul H. Zedler
Organizations
- Air Force Office of Scientific Research
- San Diego State University