Trillium kurabayashii

Other Trillium species within the region are heavily impacted by logging and significant short-term mortality caused by clearcutting, and long-term reductions in fecundity and recruitment caused by habitat degradation has been observed in related sympatric species (Jules 1998). Cascading impacts from logging have been demonstrated to have negative impacts on T. ovatum subpopulations through significant increases in deer mouse (Peromyscus maniculatus) population and subsequent seed predation (Tallmon et al. 2003). The impact of logging on Trillium populations is likely to be regionally variable as subpopulations of T. ovatum 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 long process and may require centuries. The rate of recovery of Trillium species within the region has been shown to be dependent on the number of remaining individuals which survive the disturbance event (Kahmen and Jules 2005). Additional research is needed to confirm that observations relating to T. ovatum are applicable to Giant Purple Trillium, but given the similarity of the species’ habitat requirements and distribution, it is likely that threats to forests within their distribution impact both species in a similar manner.

It is likely that this species is also adversely impacted by wildfires, elk (Cervus canadensis) predation and competition with invasive plants, such as Himalayan blackberry (Rubus armeniacus). However, there are no studies documenting these threats. More research is needed. 

Additional information is needed on population level and trend, habitat and ecology, and threats to this species. Though it is not specifically protected, it occurs in several protected areas within its range, including Redwood National Park and Redwood State Park (IUCN and UNEP-WCMC 2019). The species is included in ex situ collections at 25 botanic garden sites (BGCI 2019).