Tall bugbane (Cimicifuga elata) COSEWIC assessment and status report: chapter 5

Habitat

In the Pacific Northwest, C. elata occurs over a large geographic and elevation range. In addition, the herb and shrub layer varies greatly depending on the region. The main habitat type is moist, mixed, lowland forest with a fairly closed canopy of Douglas-fir or cedar-hemlock, however, C. elata also occurs in relatively open Abies grandis forest at mid-elevation in south-western Oregon. Cimicifuga elata never represents a dominant in the vegetation cover, and is usually found in relatively sparse understories. Elevations range from 30 m to 1600 m. This species occurs on gentle to steep slopes, requires some sub-surface moisture, often provided by creeks or rivers, and generally, aspects on northerly slopes.

In the Chilliwack River valley, Cimicifuga elata grows in shady, moist, mixed, mature (70-150 yr. old) western red cedar-hemlock forest, commonly in Thuja plicata-Polystichum munitum-Achlys triphylla communities. Cimicifuga elata also occurs in mixed Douglas-fir-Acer macrophyllum, and predominately deciduous stands. This species is associated with both Acer macrophyllum (big-leaf maple) and Alnus rubra (red alder), the prior being the more common associate. The deciduous component is extremely important, providing the perfect balance of shade and light, and moisture retention. Common associated species include Rubus parviflorus, Oploplopanax horridus, Acer circinatum, Dryopteris expansa, Tolmeia menziesii, Sambucus racemosa, Circea alpina, and Asarum caudatum.  Sites are characterized by 15-35° slopes with north, south-west, and south aspects. Cimicifuga elata also occurs in managed stands. It has been observed on road cuts and in clearcuts where there is increased light availability, and freshly disturbed mineral soil increasing the chances for seedling establishment. Plants growing on road cuts and clearcuts display increased vigor. Road cuts and clearcuts mimic natural canopy openings that are likely important to the flowering, fruiting and establishment of C. elata into new sites. 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 further restrict recruitment. Roadside maintenance activities such as mowing and spraying could reduce seed production of those plants that were initially able to establish or cause the death of seedlings (Kaye and Kirkland, 1999). Another habitat unsuitable for C. elata in managed forests is the dense shrub growth that prevails several years following clearcuts (Kaye and Kirkland, 1994). Individuals will likely not persist in sites that are extensively clearcut for this reason. During field work conducted by the Conservation Data Centre in 1997, C. elata was found to be more common in areas that were not extensively clearcut, but instead, had a balance of mature mixed-forest, deciduous stands, small clearcuts, and road cuts. In Washington, this species is likewise, mainly associated with mature or old-growth coniferous or mixed-forest, but is also observed at forest margins and on road cuts. Originally, it was thought that C. elata was a mature to old-growth dependant, but now Kaye and Kirkland (1999) describe C. elata as “light flexible” (Collins et al., 1985) rather than old-growth dependant and shade restricted.

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