Fragrant popcornflower (Plagiobothrys figuratus) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
The natural environments of Greater Victoria and Nanaimo have been substantially altered by land development. In earlier days the agricultural landscape and a less intensive management regime may have supported habitats additional to the strictly natural habitats. However, being flat and convenient, agricultural land was the first to undergo urban and residential development. In the meantime, much of the remaining natural landscape was also altered, resulting in major habitat losses that probably were the leading cause for the near-disappearance of this species from Canada.
Other factors that have possibly contributed to its decline include hydrologic alterations (e.g., wetland fills, draining, construction); roadside maintenance; competition from invasive alien plant species; and encroachment of woody species due to fire suppression.
Currently, the extremely small population size of fragrant popcornflower makes it highly vulnerable to stochastic environmental events such as drought, disease, or animal disturbance. Even under stable environmental conditions, random variation in demographic parameters (demographic stochasticity) could propel this population through fluctuations that include zero reproductive individuals, resulting in local extinction. It is unknown if there is a persistent seed bank present to help buffer such fluctuations. Fragrant popcornflower may also be experiencing local inbreeding depression, another hazard sometimes associated with small isolated populations.
Aside from the inherent demographic and genetic hazards typically associated with small population size, the greatest immediate threat to the survival of fragrant popcornflower at Hornby Island is likely competition from invasive alien plant species, especially non-native grasses found in the areasuch as Lolium perenne (perennial ryegrass), Agrostis capillaries (colonial bentgrass), Poa pratensis (Kentucky bluegrass), Aira praecox (early hairgrass), and Anthoxanthum odoratum (sweet vernalgrass). Ongoing residential development in the area also poses a major potential threat to this species and its habitat. Specific development plans for the site occupied by fragrant popcornflower are unknown at this time.
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