Trillium pusillum

Predation of subaerial structures by White-tailed Deer (Odocoileus virginianus) has been shown to depress population and reduce fecundity in Trillium grandiflorum and Trillium erectum (Augustine and Frelich 1998, Goetsch et al. 2011, Kalisz et al. 2014, Knight 2004, Rooney and Gross 2003, Webster et al. 2015), but herbivory may also provide a critical means of seed dispersal (Vellend et al. 2003). In some regions, Trillium fecundity is reduced through non-consumptive interactions with deer (Knight et al. 2009). Increasing deer populations in much of the species complex’s range are expected to result in net declines in fecundity for the taxon (Dávalos et al. 2014). In some areas with particularly high deer population, declines in Trillium population may be sufficient to trigger Threatened status under Criterion A. The specific impact of deer predation on the Trillium pusillum complex is not well studied. However, several taxa are expected to be negatively impacted by deer herbivory.

Within the range of Trillium monticola, White-tailed Deer density in Augusta and Rockingham Counties, Virginia was greater than 30 individuals per square mile in 1988. As of 2004, the population index of White-tailed Deer in Rockingham and Augusta Counties was listed as Low and Medium, respectively, on both privately held and public land. Augusta County is only slightly below the threshold for qualification as Medium in both cases. More recent data (reported from 2012-2014) suggests relative deer population abundance is moderate in Augusta County and High in Rockingham County (VDGIF 2015). Deer predation in this area is likely to result in continuing habitat quality declines for Trillium monticola which, given its restricted distribution and small total population, may be especially sensitive to herbivory. White-tailed Deer are also present in large numbers at the Savannah River Site (Johns and Kilgo 2005) and predation is likely to pose a threat to T. telmacola in this area.

Feral pigs (Sus domesticus) are likely to impact several taxa within the T. pusillum complex. Mortality and habitat quality declines caused by feral pigs have been documented among several Trillium species (Howe and Bratton 1976, Plants for a Future 2018). Feral pig populations are relatively large in much of the southern United States (McClure et al. 2015) and could present a potential threat to Trillium species anywhere within this range. The impact of feral pigs is likely to be much more severe for species which occur in wetland habitats including T. alabamicum, T. pusillum, T. telmacola, and T. virginianum. In particular, large numbers of feral pigs are present on the Savannah River Site posing a major threat to Trillium telmacola (Mayer and Brisbin 2009).

Threats which may have paradoxical impacts on individual subtaxa include forestry practices and the opening of forest canopy. Several members of the species complex are relatively tolerant of disturbance (NatureServe 2019, Swick 2019) and can occur along the margins of artificially cleared areas (utility rights-of-way, clearcut margins, etc.). Disturbance caused by large-scale forest clearance has been shown to negatively impact some taxa (including T. pusillum, and T. virginianum) (NatureServe 2019), but limited clearance of small areas may increase habitat suitability for a number of subtaxa. Silvicultural practices which promote monotypic coniferous stands may also negatively impact the some members of the species complex.

Habitat loss resulting from residential and industrial development is thought to present a threat to T. virginianum and T. pusillum (NatureServe 2019). Within T. pusillum’s range, Brunswick and Pender Counties, North Carolina have among the highest rates of urban expansion in North Carolina and predicted population increases between 2010 to 2030 are 58% and 45%, respectively (Claggett et al. 2015). Subpopulations in South Carolina may face variable impacts due to urban expansion as Dorchester County is rapidly expanding in population while Calhoun and Sumter Counties have recently experienced population declines (United States Census Bureau 2019).

Trillium virginianum is threatened by grazing (NatureServe 2019). Hydrologic changes which could alter critical wetland habitats may pose a threat for those taxa relying on these areas (NatureServe 2019). Though Trillium ozarkanum’s population is relatively stable, development and associated hydrological changes has extirpated several subpopulations in northwest Arkansas and these processes threaten additional subpopulations in southwestern Missouri (NatureServe 2019).

Competing invasive plant species may have negative impacts on some subpopulations of T. alabamicum and T. carolinianum. Chinese Privet (Ligustrum sinense) may cause population declines due to habitat modification and has been implicated in the extirpation of at least one subpopulation of T. carolinainum (NatureServe 2019).

Additional taxonomic research is required to clarify the status of several . Population monitoring is needed to inform future conservation efforts. Surveys should be conducted for subpopulations which have not been visited in many years and which may have been extirpated to better prioritize efforts. Due to the ephemeral nature of some subpopulations, particularly in the case of T. telmacola which may bloom for very brief periods prior to prostrating and becoming very difficult to observe, additional studies of the life-history of the species complex are needed. Without this information, surveys may inaccurately portray the conservation status of some subpopulations. Additional surveys are needed, including in subpopulations that have not been relocated, to better document the species complex’s range, population, threats, and population trend.

Protected status of each member of the species complex varies considerably. Inadequate protection exists for those taxa which do not occur in any protected areas (NatureServe 2019). Trillium pusillum var. virginianum is listed as Threatened in Maryland and Endangered in North Carolina (USDA, NRCS 2019). Additional long-term protection may be warranted for all members of the T. pusillum complex in Maryland, North Carolina, and eastern Virginia. Both T. p. var. ozarkanum and T. p. var. pusillum are listed as Endangered in Kentucky, North Carolina, and Tennessee (USDA, NRCS 2019).

Trillium telmacola occurs entirely within the Savannah River Site, a nuclear research facility with extremely limited public access. Though the area is protected from most forms of land conversion, control of white-tailed deer and feral pig population may be inadequate in the area (Johns and Kilgo 2005, Mayer and Brisbin 2009).

Six of the nine documented occurrences of T. palustris are in protected areas (NatureServe 2019). Trillium carolinianum occurs in protected areas in Nash County, North Carolina (three sites), and Grayson County, Virginia, though the status of the latter is unknown and it may have been extirpated (NatureServe 2019).

Systematic population monitoring should be conducted for taxa with small distributions, particularly in cases where population declines may be occurring (as with T. carolinianum) and for taxa with increasing threat levels.

Ex situ collections of the species are held at 30 botanic garden sites (BGCI 2019).