Trillium lancifolium

As with other Trillium species in eastern North America, the overabundance of white-tailed deer (Odocoileus virginianus) is the primary threat faced by Narrow-leaved Trillium (Leege et al. 2010). Loss of natural predators, reduction in hunting pressure, and land use changes causing increased carrying capacity have resulted in an increased white-tailed deer population across much of eastern North America since the mid-20^th century (Russell et al. 2001). Herbivory of early season growth causes recruitment failure in the current year and often the following year in related Trillium species, leading to long-term demographic changes and ultimately population declines (Augustine and Frelich 1998). Observed rates of herbivory for the closely related and similarly distributed T. reliquum (5.6 – 22.5%) demonstrate some subpopulations exceed the 15% threshold which is projected to cause population declines in the related species T. grandiflorum (Knight et al. 2009), and are sufficient to cause demographic shifts toward smaller stage classes indicating that long-term population decline is likely (Leege et al. 2010). Further study is needed to determine the population trajectory for the species and the impact of white-tailed deer overabundance on Narrow-leaved Trillium population. Given the long generation length predicted for the plant (estimated to be 28 years in the related species T. grandiflorum), declines as small as 0.5% may be sufficient to qualify the species for threatened status. Such declines have been observed in several subpopulations of related species under similar browsing intensity (Augustine and Frelich 1998, Knight et al. 2009, Webster et al. 2005) and are likely to be present in Narrow-leaved Trillium subpopulations. All known occurrences in Florida were heavily impacted by Hurricane Michael in 2018. The storm caused significant loss of canopy cover which was exacerbated by Tropical Storm Nestor in 2019 (Jenkins pers. comm. 2020). Though the direct impact of these events has not been studied, the loss of canopy cover is likely to result in reduced habitat suitability and sustained population declines into the foreseeable future.

Introduced species may also constitute a threat to the species. Feral pigs (Sus domesticus) are known to cause habitat degradation leading to declines in related species within the range of Narrow-leaved Trillium and likely cause population declines throughout the species’ range (Bratton 1974). Though direct competition between T. cuneatum and introduced Japanese honeysuckle (Lonicera japonica) does not appear to have negative impacts on growth, indirect impacts related to forest composition may have long-term detrimental impacts (Leege et al. 2010). Other introduced plants are likely to present a greater threat to the species including Chinese privet (Ligustrum sinense), and wintercreeper (Euonymus fortunei).

The species' preferred habitat on floodplains makes subpopulations susceptible to flooding events which could cause population declines.

Logging and silviculture operations occurring within the its range may also threaten the species (NatureServe 2019).

One occurrence of Tennessee Trillium is known to have been destroyed through conversion of habitat to a horse pasture. Following the publication of the species description, collectors have dug plants as horticultural specimens. Collection for horticultural purposes is thought to present a minor threat to the species. All known occurrences of Tennessee Trillium exist on private land and are not protected from land conversion. Deer browse has been observed at several occurrences and overabundance of white-tailed deer (Odocoileus virginianicus). Bush honeysuckle (Lonicera maakii) has been observed in the area and is likely to cause future population declines. Fungal infections which prevent recruitment have also been observed. Additional study is needed to better characterize the threat posed by fungal infection as well as to identify the cause and potential disease vectors.

The species is listed as State Endangered in Florida and Tennessee (USDA, NRCS 2019). Though not specifically protected outside of Florida and Tennessee, the species is likely to incidentally occur in one or more of several protected areas within its range (IUCN and UNEP-WCMC 2019). Subpopulations are known to occur within Talladega National Forest, Torreya State Park, Apalachee Wildlife Management Area, Crockford-Pigeon Mountain Wildlife Management Area, Oaky Woods Wildlife Management Area, and Apalachicola Bluffs and Ravines Preserve (NatureServe 2019). The species also occurs in Angus Gholson Park in Chattahoochee, Florida. Given the nature of the threats to the species (problematic white-tailed deer abundance, and logging), several of these areas offer inadequate protection to prevent further population declines. In addition to population monitoring, conservation measures should focus on control of problematic and invasive species. Some subpopulations have been identified as of particular conservation concern including those along the I-75 corridor in Georgia (NatureServe 2019). The isolated nature of the species is well suited for habitat protection measures which should be pursued in order to protect existing populations from further habitat degradation. Ex situ collections of the species are included at 12 botanic garden sites (BGCI 2019).

No formal agreements are in place protecting Tennessee Trillium’s habitat. Land conversion has already resulted in the loss of a subpopulation. The four subpopulations may face similar threat as they are not protected. Invasive and problematic species control and conservation easements are needed to prevent the extinction of the taxon.