Monitoring Michaux’s Sumac Requires More Systematic Approaches

Restoring a species requires knowledge of its population levels, geographic distribution, and long-term monitoring. This situation is especially true for Michaux’s sumac (Rhus michauxii), a federally-listed endangered shrub and one of the rarest shrubs in the southeastern United States (Fleming and Ludwig 1996). Most of the current geographic range lies in the lower Piedmont and upper Coastal Plain of North Carolina, although the largest concentration of plants is at Fort Pickett, Virginia (Emrick and Jones 2008). Since time of discovery by Andre Michaux in 1794 in Union County, NC, Michaux’s sumac has always been rare (Boynton 1901, USFWS 1993). Habitat loss and degradation from urban development and current policies of fire suppression have exacerbated the situation, allowing other woody plants to establish and making many locations too shady for Michaux’s sumac to compete successfully for resources (USFWS 1993).

Like other sumacs, Michaux’s sumac is maintained by periodic disturbance (USFWS 1993, Emrick and Jones 2008). It is distinguished from other native sumacs of eastern North America by short stature (0.3–0.9 m), coarsely serrated or crenated leaves, and densely pubescent twigs and leaves. At most locations, Michaux’s sumac consists of single-sex clones (USFWS 1993). Reproduction is essentially all asexual from root sprouts (Braham et al. 2006). As an endemic species with a dioecious flowering habit and geographic barriers between populations, sexual reproduction of Michaux’s sumac is rare; a situation that severely limits the natural expansion of the geographic range and confounds restoration efforts.

The U.S. Fish and Wildlife Service (1993) reported that over the last 200 years Michaux’s sumac had been found at 31 locations in North Carolina, but only 20 locations still contained plants in a 1993 survey. Nearly one-half of the locations in North Carolina are found in only one county (Richmond). About one-half of the known locations are along roads or rights-of-way. Because Michaux’s sumac is clonal, few genotypes (one at each location) may exist in North Carolina. These situations suggest that Michaux’s sumac may be vulnerable to chance disturbances and outbreeding depression (Levin et al. 1996).

The objective of this project was to determine how the number of locations with live plants and the number of plants at each location has changed over time. We wanted to determine whether the regional population of Michaux’s sumac is increasing, decreasing, or stable. Because restoration of Michaux’s sumac is most critical in North Carolina, we concentrated our assessment on North Carolina, but also requested information from the Natural Heritage Programs in Virginia, South Carolina, Georgia, and Florida.

To assess the number of locations and plants over time, we examined the records (elemental occurrences) kept by the Natural Heritage Program of North Carolina. With the exception of a few historical notes, record keeping began in 1980. The records indicated that regular visitation of all locations was not the norm. Some locations were visited only once, but others were visited up to eight times since 1980, a situation that made periodic comparisons impossible. We also noted several other confounding issues: the number of plants at 15 locations (almost half) was sometimes only roughly estimated, usually recorded as “over 50” or “over 100”; the records contained references to “subpopulations” within some locations; the meaning of subpopulation was not completely clear, but we suspected it referred to groups of plants somewhat separated at a particular location; the number of sumac plants at five locations had been augmented by planting; the records also included four locations where the plant was actually the hybrid (Rhus × ashei) with smooth sumac. Thus, we concluded that we could not accomplish our original objective, and instead decided to update the records by counting the number of plants at all known locations in a short time period. We hope that our update will provide a benchmark for future studies.

Between May 2005 and September 2006, we visited 36 of the 38 locations that might contain live plants as indicated by the NC Natural Heritage Program records. Two locations were not included; one Moore County...