Occurrences CommentsAbout 60 known occurrences with additional populations expected with further survey.
Virginia: The number of Virginia documented occurrences has been revised downward to 17 by using a 1 km separation distance between occurrences (J. Townsend, VA Dept. of Conservation and Recreation, 2006 pers. comm.) These 17 occurrences had previously been recognized as 30 occurrences, with an occurrence at that time being equal to the plants within a discrete pond or wet meadow. It is expected that additional survey work will find more occurrences within the 21-80 range; some of these may be within the more disturbed farm pond type of habitat. As most of the sites in Virginia have not been visited since 1995, it is not known how many are currently extant. Based on what was known at the time the draft Recovery Plan was written in 2000 there were 4 sites where plants had not been seen over several years of surveys (U.S. Fish and Wildlife Service 2000). The Virginia occurrences were located during extensive survey work from 1985 to 1995 in over 100 limestone sinkhole ponds along the western edge of the Blue Ridge Mountains in the Shenandoah Valley of Virginia (FWS 1998).
Missouri: In 2000, a population of a Helenium sp. in a sinkhole pond near Pomona, Missouri , was determined to be H. virginicum, based on genetic work conducted by Simurda and Knox (2000). By early 2006, 44 native occurrences had been found within 6 counties: Howell (23), Oregon (1), Shannon (15), Texas (3), Webster (1), and Wright (1). All are within the Ozark Highlands in southern Missouri. The 1 km separation distance was used to define occurrences (Tim Smith, Missouri Dept.of Conservation, pers. comm. 2005). In addition, plants have been introduced at 9 sites, 3 on state lands and the remainder private. Probably 50% of the potential habitat remains to be surveyed.
Threat Impact CommentsIn Virginia the long-term viability of existing populations is primarily threatened by human-induced disruptions of hydrologic regimes, particularly by encroaching agriculture, residential land development, and logging (Van Alstine 1991; J. Knox, C. Williams pers. obs.). In addition, a private site and adjacent sites on the George Washington National Forest are sporadically impacted by off road vehicles (e.g., during summer 1991 on the private land; J. Knox, C. Williams, pers. obs.).
Exotic organisms may pose threats to H. VIRGINICUM populations in the near future. Purple loosestrife, LYTHRUM SALICARIA, is slowly spreading through Virginia and may eventually invade some H. VIRGINICUM sites, especially following disturbances to hydrologic regime and/or substrate. The introduced Spongy Moth (Lymantria dispar), is currently defoliating large areas of the George Washington National Forest and adjacent lands but it is unclear whether the Spongy Moth will negatively impact H. VIRGINICUM populations. For example, as H. VIRGINICUM is shade-intolerant, defoliation of trees and shrubs that grow on the periphery of sinkholes may increase light availability and allow H. VIRGINICUM to expand into areas from which it was formerly excluded.
The following paragraphs are taken, with modifications, from U.S. Fish and Wildlife Service (2000):
The most serious threat to H. virginicum appears to be habitat loss, most often arising from changes in the natural hydrological regime of the sinkhole pond habitat. Four of the sites, three of which are grazed by cattle, have had a portion of the wetland deepened to create a permanent pond; prior to being excavated, much of this section once undoubtedly supported H. virginicum and so loss of some habitat has occurred. In contrast, actions have been taken at some of the Virginia sites to stop or lessen the periodic inundation. Significant ditches have been dug at two sites, with smaller ditching at three sites. Ditching and plowing occurred at one site in the past, and some evidence of the ditch remains, but does not significantly affect the hydrologic regime. Portions of the sites at 2 sites have been filled in. It is safe to assume that the pressure to control seasonal flooding will only increase, as the area of the Shenandoah Valley where the Virginia populations of H. virginicum are found is experiencing rapid growth, particularly in the building and expansion of residential subdivisions.
In addition to obvious hydrological alterations made directly to the sinkhole ponds, off-site actions may affect the hydrology of the ponds. Input from groundwater sources may be decreased by withdrawals for wells for adjacent developments such as subdivisions. Overland surface water flow may be altered by activities such as timber harvesting or road building in upslope areas. Little is known about the relative importance of groundwater vs. surface flow to the hydrological regime of the sinkhole ponds, but preliminary research suggests that the relative importance of these water sources is unique for each pond (E. Knapp, Washington and Lee University, pers. comm.).
A variety of site-specific threats to H. virginicum from habitat loss have appeared over the last ten years. The Virginia Department of Transportation (VDOT) has proposed to widen to four lanes Route 340, a currently two lane north-south corridor on the east side of the Shenandoah Valley. A portion of one site in Augusta County is immediately east of Route 340. The Virginia Department of Conservation and Recreation's Division of Natural Heritage reviewed the proposal for this project in 1991 and recommended against any road widening to the east in the area of the pond and further recommended that VDOT consult with the U.S. Fish and Wildlife Service before any construction began. While the long range plans still include widening Rt. 340 to 4 lanes in this section, this project is not active; VDOT will coordinate with USFWS whenever the project becomes active (S. Stannard, VDOT, pers. comm.)
Another H. virginicum population is near the site of silos built in the early 1990's that are used to store septic waste. This waste is eventually dumped on the ground elsewhere on this landowners' ridge-top property and not near the H. virginicum site. However, in a 1995 site visit by DCR-DNH a large pile of soil was present on the north side of the shallow basin that supports the H. virginicum population. The landowner was considering pushing the soil into the seasonally wet basin to level it out, but was agreeable to not do that. In a 1997 site visit the pile was still present and was larger than in 1995. In 1995 and 1997, it was noted that sediment from the pile had washed into the edge of the pond site, creating different soil conditions in that area and making it more favorable for weedy species (DCR-DNH database).
Mowing occurs in at least 3 of the Virginia sites. Continued mowing may provide beneficial effects to the species; a site that is one of the largest if not the largest and densest population, has been periodically mowed and bush-hogged by the landowner for an extended period of time. Repeated mowing before seed is set and the seed bank is replenished, may lead to local extinction as vegetative plants die out and the seed bank ultimately becomes depleted.
Herbivory does not appear to be a problem; however, the threat to H. virginicum from cattle grazing needs evaluation. Large populations of H. virginicum co-exist in three sites with cattle grazing. This suggests that the species may respond favorably to limited amounts of disturbance. Knox et al. (1999) tested the hypothesis that H. virginicum is unpalatable to generalist herbivores in a common garden study; none of the H. virginicum plants were grazed by either vertebrate or invertebrate herbivores. Knox notes that this is consistent with reports of toxicity in other Helenium species associated with the presence of sesquiterpene lactones (Hesker 1982, Anderson et al. 1983, Anderson et al. 1986, Arnason et al 1987). Helenium virginicum has been shown to contain a sesquiterpene lactone, virginolide (Herz and Santhanam 1967). According to J.S. Knox (pers. comm.), the leaves of H. virginicum are bitter-tasting; selective grazing by cattle of more palatable associated species therefore may eliminate plant competitors. However, other effects on H. virginicum from cattle grazing such as the increased nutrient loads, soil compaction, and trampling of plants are unknown. As the soils of the H. virginicum sites have been found to be nutrient-limiting (Knox 1997), long-term nutrient enrichment from cattle could ultimately create more favorable habitat for other plant species.
With federally listed wetland species, the federal permitting process carried out by the US Army Corps of Engineers (USACOE) under authority of the Clean Water Act of 1977, is often the point at which proposed actions can be reviewed in light of their effect on a federally listed species and protection actions can be recommended. The isolated and often small seasonally wet habitat of Helenium virginicum, however, does not currently have direct federal protection. United States vs. Wilson 133 F. 3d 251(4th Cir. 1997) ruled that the USACOE has no jurisdiction over isolated water bodies that have no surface connection with any tributary stream that flows into traditional navigable waters or interstate waters. Nationwide Permit 26, under federal wetlands regulations (56 CFR 59134-59147, Part 330-Nationwide Permit Program), which has applied to headwater areas and isolated wetlands, is currently being revised including a lower minimum acreage (1/10 acre); the Norfolk District of the USACOE is proposing a regional minimum threshold of 1/4 acre (E. Gilinsky, DEQ, pers. comm.). These lower minimum acreages, however, will not apply to the Helenium virginicum habitat if the ruling in U.S. vs. Wilson stands.
Currently, so-called Tulloch ditching, draining by ditching in which excavation occurs by mechanical means that do not require placing excavated material into a wetland and in which the material is lifted and hauled to an upland disposal site, does not require that USACOE be notified or a permit obtained. Major ditching has been used at three of the H. virginicum sites to control the seasonal flooding with more minor ditching used at another three sites.
As most of the populations of H. virginicum are on private lands, the current legal protections in place for this species will not be adequate to insure the long-term survival of H. virginicum. The effects of future regulation changes are not known.
Extremes in the fluctuating hydroperiod of the sinkhole ponds could, when preceded by low investment in the seed bank, result in the local extinction of populations. Extended drought at a site could make a site more favorable for colonization by other plants previously hampered by the periodic inundation of the site. This would include tree species, which could result in increased shading within the site and so reduce the areas favorable for H. virginicum. An extended period of inundation, coupled with development of a floating vegetation mat, such as occurred at one site (Knox 1997), could lead to local extinction if an insufficient seed bank existed to recover from the death of the vegetative plants. Either of these extremes in hydroperiod could result from normal variability in weather patterns or from larger scale climate changes, of either natural or human origin.
If found to hold true for other populations of H. virginicum, the self-incompatible breeding system of H. virginicum found in one of the populations may eventually lead to local extinction at sites with low population numbers as the chance of successful pollination decreases (Messmore and Knox 1997).
In Missouri threats include grazing and/or trampling of plants in the pasture sites and haying of the plants during the growing season. Herbicide or plant growth hormones used on roadside pose a threat to the roadside populations.