Trille à feuilles ovées

Logging is the primary threat to Pacific Trillium with significant short-term mortality caused by clearcutting, and long-term reductions in fecundity and recruitment caused by habitat degradation (Jules 1998). Short-term declines are significant in all studied plots. In clearcut forests in the Siskiyou Mountains of Oregon, 75% of observed plots contained no individuals younger than the most recent clearcut date suggesting such a practice is likely to result in complete extirpation of adults within a given locality (Jules 1998). Demographic data suggest that 2.4% of adult Pacific Trillium plants survive clearcutting and replanting of a given plot.

Cascading impacts from logging have been demonstrated to have negative impacts on remaining Pacific Trillium subpopulations through significant increases in Deer Mouse (Peromyscus maniculatus) population and subsequent seed predation (Tallmon et al. 2003). Pollen limitation among plants occurring in edge habitats is also evident and results in reduced seed set relative to the increased availability of resources in these edge environments. These impacts are caused less by the fragmentation of habitat than by the increase in forest edge habitat within which the species has lower levels of recruitment (Jules 1998). Pacific Trillium is intolerant of silviculture operations and is absent from observed tree plantations in the Siskiyou Mountains of Oregon (Jules 1998).

The impact of logging on Trillium populations is likely to be regionally variable as subpopulations have been observed to survive clearcutting episodes in the Oregon Coast Range and the western slope of the Cascade Mountains. This variation may be attributable to levels of summer precipitation (Jules 1998). Impacts caused by logging may be more severe in the southern portions of the species’ range where conditions are relatively arid. In addition, the impacts of climate change, which are predicted to exacerbate interannual variation in precipitation and reduce soil moisture during drought (Diffenbaugh et al. 2015), may increase the portion of the range within which logging has a severe impact. Population recovery following disturbance events is a very long process and may require centuries. The rate of recovery has been shown to be dependent on the number of remaining individuals that survive the disturbance event (Kahmen and Jules 2005).

However, Pacific Trillium subpopulations in California are currently robust and there is no indication of widespread decline.

In addition to threats posed by logging in adjacent areas, Hibberson's Trillium is threatened by the possibility that climate change (Diffenbaugh et al. 2015) might affect the hydrology of the seep habitats where it occurs.

Throughout its distribution the species occurs in protected areas including several wilderness areas (Siskiyou, Kalmiopsis, Sky Lakes, Mount Hood, Mount Washington, Mount Jefferson, Mount Adams, Wild Sky, Henry M. Jackson, Glacier Peak, and Mount Baker) and national parks (Glacier, Olympic, Mount Rainier, Crater Lake, Redwood, and Yellowstone) within which the species is protected from logging (IUCN and UNEP-WCMC 2018). Protection of forest habitat which has never been logged and forest management strategies that limit the amount of forest edge habitat are necessary to promote the recovery of Pacific Trillium in portions of its range (Jules 1998). Current stand rotation rates within the Pacific Northwest (60 to 120 years) are inadequate for population recovery following clearcutting events (Kahmen and Jules 2005). Since survivorship of Pacific Trillium is very low following clear-cut logging, and population recovery is dependent on surviving subpopulations, changes to management strategies should focus on retaining reservoir subpopulations in sufficiently large undisturbed patches, which may allow for recruitment within adjacent disturbed habitats (Kahmen and Jules 2005).

Hibberson's Trillium is protected by the Dogwood, Rhododendron and Trillium Protection Act for all of Canada. At least one of its subpopulations occurs within the protected Hesquiat Provincial Park, which was established specifically to help to protect this species (Anonymous 2003).