Tall bugbane (Cimicifuga elata) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Cimicifuga elata has both intrinsic biological limitations, and an uncertain future under current logging regimes in the Pacific Northwest. This combination of limiting factors raises ample concern for its conservation.
Populations of C. elata are small, and sporadically distributed over the landscape. Small populations are susceptible to low genetic diversity and imminent extirpation. In addition, C. elata is relatively much less attractive to pollinators than other flowering plants, and therefore, receives fewer visits, and has less reproductive success. Further limiting this species is the lack of a specialized seed dispersal mechanism.
In addition to these biological concerns, the increasingly fragmented landscapes of the forests of the Pacific Northwest threaten the continued persistence of C. elata. All of the sites in which C. elata occurs are managed stands. Natural processes, such as fire and tree disease, that create small canopy gaps and that likely allow C. elata to flower and get established in new sites are less frequent events in managed forests (Anonymous, 1996). Instead, managed forests contain small to large clearcuts and roads, which may or may not adequately mimic the natural gaps. On road cuts and in clearcuts there is increased light availability and freshly disturbed mineral soil increasing the chances for flowering, fruiting, and seedling establishment. Plants growing on road cuts and in clearcuts benefit from the high light levels and display increased vigor. However, road cut habitats may be initially favorable for C. elata establishment, but unlike small natural openings in the canopy, may have numerous disruptions that may restrict further recruitment. Roadside maintenance activities such as mowing and spraying could reduce seed production or cause the death of new seedlings (Kaye and Kirkland, 1999).
In addition, short-term survival of adult plants in clearcuts is questionable as forest succession takes place. Kaye and Kirkland (1994) found that populations of C. elata were notably absent from young 15-30 year-old managed stands, which was corroborated by field work done by the Conservation Data Centre in British Columbia. In one site where C. elata had previously been sighted, the forests have been extensively clearcut several years ago and the current structure was apparently unsuitable. Furthermore, re-colonization back into these sites may be unlikely due to the low reproductive success and poor dispersal ability of this species. In addition, populations on steep slopes may not respond well to clearcutting initially as it disturbs the forest floor and upper soil horizons (Kaye and Kirkland, 1999). Herbivory also increased on plants in clearcuts, along edges and in selectively thinned stands in United States populations.
Cimicifuga elata responds well to the increased light levels of managed forest activities, but may also be threatened by those activities and is definitely threatened by conditions of early forest succession. Therefore, it is likely to be more common in areas that are not extensively clearcut, but instead, have a balance of mature mixed-forest, deciduous stands, small clearcuts, and road cuts, representing a high diversity of different habitats, one of which may suitable for it during various stages of its life cycle. However, the long-term viability of this species even under the best management regime possible has not been studied and therefore, is an unknown.