Spalding's Catchfly: A Monitoring Challenge

Publication Type:

Journal Article

Authors:

Janice Hill

Source:

Sage Notes, Volume 39, Issue 3, p.6 pp. (2017)

Call Number:

A17HIL02IDUS

Keywords:

demographic, detectability, dormancy, monitoring, Silene spaldingii, Spalding’s catchfly, timing

Abstract:

It is a common belief that plants are easier to monitor than animals; they can’t run away. Most plant demography studies assume all plants will be detected, i.e., their detection probability = 1; however, values <1 are widespread in demography studies and can lead to biased results (Kéry and Gregg 2003). Some plants exhibit prolonged dormancy in which a plant remains alive but invisible belowground for one or more growing seasons. This presents an obvious detection problem. Tracking marked plants in permanent plots for consecutive years is needed to distinguish dormant from dead plants. Additionally, for plants with an unobservable dormant stage, all plants emerging aboveground for a growing season need to be detected with certainty or dormancy will be overestimated (Kéry et al. 2005). Aboveground plants, however, often go undetected as well due to such factors as stage class size, surrounding vegetation, herbivory, and observer ability.

The Threatened plant Spalding’s catchfly (Silene spaldingii) is a long-lived perennial forb with whitish flowers and glandular stems that occurs in Palouse and canyon grasslands, sagebrush steppe, and open-canopy pine stands of the inland Pacific Northwest. Aboveground portions of the plant die back completely over winter and emerge in late May/early June as either rosette plants, single-stemmed plants, or multi-stemmed plants from an underground stem, the caudex. Flowering occurs from mid-July into October. This species is known to exhibit prolonged dormancy (Lesica 1997).

Most surveys and monitoring have been conducted at flowering time. A Montana demographic study conducted at flowering time reported high levels of prolonged dormancy, up to 50% annually, and considered all rosettes to be recruits (Lesica 1997). Other researchers also reported high levels of prolonged dormancy and considered rosettes to be recruits or questioned whether rosettes can be adults (Taylor et al. 2012, Luke 2013). Studies of this species in Idaho canyon grasslands, however, documented: 1) several stemmed plants flagged early in the season had disappeared completely by flowering (Hill and Gray 2000), and 2) several rosette plants were connected to mature caudices and/or occurred at sites that supported reproductive stemmed plants in previous years (Hill and Fuchs 2003, Hill and Weddell 2003). This indicated that all aboveground plants may not be detected at flowering and that rosette plants may be adult plants.