Sampling time influences detectability and demographic estimates of the rare herbaceous geophyte Silene spaldingii Wats. (Caryophyllaceae)

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1. Most surveys and demography studies for the Threatened plant Silene spaldingii have been done at flowering time. We conducted two separate demography studies that followed a total of 728 plants for nine to ten years and included two complete sampling periods each growing season: one soon after emergence in early June and one at flowering time in late July/early August. 2. It is generally accepted that this species has high levels, 30-50%, of annual prolonged dormancy (survival of plants belowground one or more years) and that all rosettes are recruits. In contrast, our results showed much lower incidence of prolonged dormancy, 9-11% annually, and rosettes were not only recruits but also a major, vegetative, adult stage class for this species. 3. Nearly all (>99.8%) aboveground plants were present and detected at early sampling. Approximately one-third of them were rosettes, the large majority of which, 85-95%, were established adult plants that had been present as stemmed, rosette or dormant plants in previous years. 4. Large numbers of plants present early in the season, 43%-45%, completely disappeared or became undetectable by flowering time; this value increases to 54-58% if all senescent plants are included. Detectability of all aboveground stage classes declined considerably by flowering time (time-dependent) and affected the small, ephemeral, rosette stage disproportionately (stage-dependent). 5. If we had sampled only at flowering time as most studies do, many aboveground plants present earlier in the growing season would not have been detected resulting in biased demographic estimates, including overestimates of dormancy by two to three times. 6. Synthesis: The inclusion of an early sampling period in demography studies for S. spaldingii was essential for discovering new life history information, revealing detection problems associated with aboveground plant stages, and obtaining unbiased demographic estimates. Not detecting inconspicuous stage classes and decreases in detectability of aboveground plants during one growing season are likely common events, yet few studies have examined these issues and their effect on demographic estimates.

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Reference Code: U13HIL01IDUS <br>

Full Citation: Hill, J.L. and E. O. Garton. 2013. Sampling time influences detectability and demographic estimates of the rare herbaceous geophyte Silene spaldingii Wats. (Caryophyllaceae. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise, Idaho and Department of Fish and Wildlife Sciences, University of Idaho, Moscow, Idaho. 39 pp. <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: {Silene spaldingii}