Rayless goldfields (Lasthenia glaberrima) COSEWIC assessment and status report 2000: chapter 7

Population Sizes and Trends

Search effort

The range of potential habitats for rayless goldfields was determined by reference to herbarium label information associated with specimens from Oregon and California. Although the species may range inland in Oregon and California it, like many other vernal pool species, is quite unlikely to occur more than a few metres from the ocean’s edge in Canada.

Over the past decade, virtually all intact shoreline areas have been examined, from Whiffen Spit (8 km northwest) to Swartz Bay (45 km northeast). However, the specific area where the population was found had received only limited attention from local botanists prior to 2003. The search effort included most islands and islets offshore of Victoria and the Saanich Peninsula. Within this search area most large complexes of vernal pools and seeps on shoreline sites have been examined several times. Suitable habitat is scarce or absent west of Whiffen Spit because of differences in coastal geomorphology and sharp climatic gradients. Shoreline vernal pool and seepage habitats are also relatively uncommon beyond the northeast limits of the main search area. Most of the vernal pools and seeps northeast of the main search area that have known occurrences of other rare plants have been searched for rayless goldfields, as have most vernal pool complexes large enough to be identified using air photographs. The most northerly sites searched are near Nanoose Bay (a little over 100 km to the north). While it is possible that there are undiscovered Canadian populations of rayless goldfields, almost all suitable sites have been surveyed.

Suitable sites have been surveyed repeatedly since the early 1980s in a series of projects designed to document the distribution of rare plants of seepage sites and vernal pools on southeast Vancouver Island and the Gulf Islands. The principal investigators included Adolf and Oldriska Ceska, Matt Fairbarns, Hans Roemer, Jenifer Penny, Harvey Janszen, Frank Lomer and the late George Douglas.

Although Lasthenia glaberrima is a relatively inconspicuous plant easily overlooked during casual botanical inventories, this status report was only prepared after a directed survey by botanists familiar with the species. This survey effort includes annual searches specifically for it (approximately 6 person-days in 2003, 8 person-days in 2004, 4 person-days in 2005 and 5 person-days in 2006). These efforts included unsuccessful surveys of the many sites that had other rare plants of vernal pools and seeps (Figure 4). Despite the concentrated effort, no new populations were discovered.

Figure 4. Negative search results for Lasthenia glaberrima, 2003-2006.

Figure 4. Negative search results for Lasthenia glaberrima, 2003-2006.

Abundance

The single Canadian population, at East Sooke Regional Park, consisted of 21 mature plants in 2006 (Table 1) as compared to about 200 plants when first discovered in 2003.

Table 1. Trend in the Canadian population
Observation Date Population Extent
(actual area occupied)
Number of Individuals
May 25, 2003 20 m2 180 +/- 20
May 18, 2004 8 m2 75 +/- 10
June 3, 2005 4 m2 20
June 8, 2006 10 m2 21

Fluctuations and trends

There is no long-term monitoring record but short-term data indicate a decline in population size (Table 1). It is uncertain whether this reflects a decline that may continue or if the most recent population size reflects a low point in a fluctuating population. It is known that other annuals may experience significant natural fluctuations in population sizes (Harper 1977). Species of Lasthenia are particularly prone to dramatic fluctuations in response to variations in annual rainfall and duration of ponded water as exemplified by L. conjugens at Ford Ord, where population sizes varied from 500-1500 in 1998; 56,000 in 1999 and 162,500 in 2000 (U.S. Federal Register 2003).

Rescue effect

The nearest reported population is from near the Columbia River in southern Washington. The site is about 300 km from the nearest point in Canada and about the same distance from the only known site in Canada. There is little chance of seed dispersal across such distances since the seeds lack a coma or any other structure to aid in long-distance dispersal.

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