Dr. Susan E. Meyer
Population Biology and Seed Bank Dynamics of Rare Plants
Dana Quinney, Idaho Army National Guard, Boise ID
Teri Knight, The Nature Conservancy, Las Vegas NV
Two long-term population and seed bank dynamics studies of rare plants have developed out of a career-long interest in the ecology of rare and edaphically restricted plants.
The first species, Arctomecon californica (Golden Bearclaw Poppy) is a perennial herb of gypsum badlands in the eastern Mojave Desert. It is relatively short-lived but has high seed production and forms a persistent seed bank. Our retrieval studies at two sites near Las Vegas, Nevada show that the seeds can survive long-term exposure to soil temperatures as high as 60C. After seven years in the soil, most of the seeds are still viable, and a large fraction remain dormant and still not responsive to environmental cues like chilling. This persistent seed bank explains how populations thought to have become extinct can re-establish during years of high winter precipitation.
The second species, Lepidium papilliferu (Slickspot Peppergrass) is a facultative summer annual/biennial of the sagebrush steppe country of the southwestern Snake River Plains, Idaho. It too is edaphically restricted, found only on and near 'miniplayas', which are areas where water collects in winter, and where clays and salts tend to accumulate. These 'miniplayas' are usually devoid of perennial vegetation because of winter flooding, but they hold water into the summer, making it possible for this summer annual to survive in a climate of minimal and unreliable summer rainfall.
In occasional years, there is sufficient summer rainfall for the potentially biennial cohort to survive--these biennial plants overwinter and flower the following spring, usually setting far more seeds than the annual cohort. But at least as often, the summer is so dry that not even the annual cohort survives to set seed. In this precarious environment the need for a persistent seed bank to buffer against year to year variation in reproductive success is absolutely essential to survival.
Our research focuses on modelling the effects of environmental variation on population dynamics of slickspot peppergrass, and using the model to distinguish natural variation in population levels from declines due to human-related causes.