Round-leaved greenbrier (Smilax rotundifolia) COSEWIC assessment and status report: chapter 7

• Previous page
• Table of contents
• Next page

Population Sizes and Trends

Search effort

The authors spent five days in the field in Ontario during June and July 2006, but a considerable portion of this time was spent attempting to secure access to the properties. In only two cases were we unable to locate the species at sites we accessed, and Smilax is quite possibly still extant at both. No exploratory searches of areas of suitable habitat where this species had not been previously reported were undertaken. Specific data on the 2006 field surveys (including search effort per site) are on file with COSEWIC and the Ontario Natural Heritage Information Centre (NHIC), as are the data from the surveys undertaken by the OMNR in 2004 and 2005.

The Niagara Peninsula Conservation Authority (NPCA) has completed extensive surveys during 2006 and 2007 as part of a Natural Areas Inventory. In 2006, field crews visited 76 properties in the municipality of Port Colborne covering 439 ha. In 2007 they surveyed four regions in the Niagara Peninsula covering 179 sites and 868 ha. This represents a total of 255 sites and 1307 ha. Although not every hectare of habitat has been searched in the Peninsula, the field crews are familiar with the species and have looked specifically for it together with other rarities in the region. New populations of some COSEWIC-listed species have been found but none for round-leaved greenbrier, a conspicuous climbing vine (Albert Garofalo, pers. comm. to M.J. Oldham 2007). Few additional populations are likely to be discovered in the Niagara peninsula.

No fieldwork was conducted in Nova Scotia for this report. The species is not tracked by the Atlantic Canada Conservation Data Centre nor the province due to its seemingly secure (S4) ranking in Nova Scotia.

Abundance

The species is locally common in Nova Scotia.  It occurs at >50 sites spread throughout four counties. Some of the populations are in protected areas, including Kejimkujik National Park and Tobeatic Wilderness Area (Nova Scotia Museum of Natural History and Nova Scotia Department of Natural Resources’ significant habitat database, as cited in COSEWIC 2001. The populations appear to be stable, at between 3,000 and 10,000 individuals (Elderkin, pers. comm. 2006). These values do not represent actual counts but merely rough estimates of the number of plants/root crowns that may reflect the frequency of plants observed in Nova Scotia. It is highly likely that the actual total number of discrete genetic units (distinct plants) of this clonal species is much smaller than the estimates given. The degree of underground connectivity between crowns, consisting of one or more aggregated stems arising from a given rootstock, cannot be readily determined in the field.

Within Ontario, there are 14 sites at which round-leaved greenbrier has been conclusively recorded (see Table 3; and Figure 4). Of those, one is known to be extirpated, and eight have been verified as extant within the past three years (Table 3), leaving five populations possibly extant but not recently confirmed. The “recently verified” ratio is conservative, as several landowners denied fieldworkers access to their properties in 2006. Based on earlier reports (e.g. Ambrose 1994), at least some of these unconfirmed populations are likely still extant.

There are four additional sites described as “not recently verified” in Soper and Heimburger (1982--two from Chatham-Kent, and two from Middlesex), but without supporting documentation. Plants at these sites may be extirpated or the reports may be based on misidentifications. There is no population, extant or otherwise, known from Rondeau Provincial Park, despite a dot there in Soper and Heimburger (Dobbyn pers. comm. 2006).

Herbarium acronyms follow Holmgren and Holmgren (1998).

It is difficult to determine the number of individuals within a given population due to the clonal nature of this species. At least one population (Site 10), supports hundreds to thousands of crowns and at least three others (Sites 5, 6, and 12) support dozens of crowns. The provincial total is between approximately 1000 and 5000 crowns (each of which may or may not be clonally connected to other such crowns). A more realistic measure of numbers of distinct “individual” plants for Ontario is likely in the order of several hundreds of clones (distinct plants) rather than thousands. This is surmised from the fact that plants at 6 of the13 extant Ontario sites are all of single sex and conceivably represent one or only a few genetically distinct colonies having developed from separate propagules originally introduced at the sites. The fact that the colonies tend to be in concentrated patches and not widely scattered throughout the woodlands also argues for localized introduction and vegetative spread forming discrete localized colonies comprised of crowns whose numbers have increased through vegetative spread. Such clonal species reproducing vigorously through vegetative means can persist and spread in an area likely over many decades and perhaps even centuries to form colonies of substantial size.

Fluctuations and trends

Although the populations in Nova Scotia appear to be stable, the data for Ontario are too sparse to allow the determination of concrete trends in the province. In general, the populations appear roughly comparable between the two assessments (Ambrose 1994 and this report). The discovery of four new populations and several new subpopulations at known sites between the two assessments suggest a positive trend for this species in Canada; however, these new populations most likely represent the discovery of previously undocumented populations rather than recent colonizations.

This trend is also weakened by the degradation of known sites and by the inability of fieldworkers to secure permission to confirm several key Essex region populations.

Rescue effect

No specific data are available on this topic, but one could speculate that rescue is possible for the Ontario populations. Although the frequency and distance of bird dispersal of round-leaved greenbrier has not been documented, it is assumed that potentially long-distance dispersal may be possible, especially since large populations of this species occur in the United States south of Ontario very close to the Canadian border. The species occurs along the edges of Interstate 90 West in New York State, just across the lake from Fort Erie (Garofalo pers. comm. 2006). However, round-leaved greenbrier is dioecious and the establishment of a new sexually reproducing population would require two seeds of different sexes to germinate and survive at the same site. It is conceivable that bird droppings could consist of mixed gender seeds originating in the northern US from populations not too distant from some of the Canadian sites. The deposit of such seeds representing a rescue event would likely occur extremely infrequently.

The populations in Nova Scotia are considerably disjunct from those in the northeastern United States with little chance for rescue.