Round-leaved greenbrier (Smilax rotundifolia) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Across its range, round-leaved greenbrier grows in a wide variety of habitats, ranging from moist woods, to heath balds, rhododendron thickets, and old fields (Carey 1994). In Ontario, this species typically occurs in moist to wet wooded habitats, often on sandy soil. In a study of open habitats in Connecticut (Niering and Goodwin 1974), round-leaved greenbrier clones grew significantly faster in moister habitats. The authors attribute the slow growth on xeric sites to both drought stress, and the impacts of lagomorph herbivory. Slightly closer to the Ontario populations, round-leaved greenbrier has been observed as locally abundant in xeric sands with largely open canopy in southwestern Michigan (Brewer et al. 1973).

Round-leaved greenbrier is an understorey component and a pioneering successional species (Smith 1974). Forest openings and surface disturbance may be required for effective seedling establishment, and the species appears to particularly favour more open woodland habitats (for example: Brewer et al. 1973). In a study by Hall and Kuss (1989) in Virginia, round-leaved greenbrier was found to be more important close to trails than in inaccessible areas, supporting the idea that it prefers openings, and suggesting that it is resistant to disturbance (Carey 1994).

The Ontario populations are within the Deciduous Forest Region (Rowe 1972), also known as the Carolinian Floral Zone (Scoggan 1978-1979) and the Moderate Temperate Ecoclimatic Province (Ecoregions Working Group 1989). Following the broad COSEWIC classification of terrestrial habitats, round-leaved greenbrier occurs, in Ontario, in the Great Lakes Plains National Ecological Area (see http://www.cosewic.gc.ca/images/cdn_National_ecological_e.jpg). There is no evidence that it was ever common within this region.

Based on fieldwork for the original report (Ambrose 1994), the frequently associated tree and shrub species in Ontario are:

  • Acer rubrum
  • Quercus rubra
  • Quercus palustris
  • Carpinus caroliniana
  • Fraxinus americana
  • Sassafras albidum
  • Quercus alba
  • Hamamelis virginiana
  • Nyssa sylvatica

Occasional associates:

  • Fraxinus pennsylvanica
  • Ulmus rubra
  • Quercus bicolor
  • Acer saccharum
  • Acer saccharinum
  • Fagus grandifolia
  • Viburnum acerifolium
  • Cornus florida
  • Castanea dentata

Infrequent associates:

  • Populus grandidentata
  • Populus deltoides
  • Betula alleghaniensis
  • Liriodendron tulipifera
  • Prunus serotina
  • Tilia americana
  • Ulmus americana
  • Carya laciniosa
  • Carya glabra
  • Carya ovata
  • Juglans cinerea
  • Vitis riparia
  • Cornus racemosa
  • Lindera benzoin
  • Zanthoxylum americanum
  • Smilax tamnoides

Round-leaved greenbrier has been observed with Cornus florida (COSEWIC Endangered), Eurybia divaricata (COSEWIC Threatened), Juglans cinerea (COSEWIC Endangered) and Castanea dentata (COSEWIC Endangered). Arisaema dracontium (COSEWIC Special Concern) was also present at Site 1, where Smilax was not relocated in 2006, but where it may well still be extant. Other species listed as provincially rare (S1 through S3) by the Natural Heritage Information Centre (Oldham 1999) that have been seen to occur in the vicinity of round-leaved greenbrier in Ontario include: Carya glabra (S3), C. laciniosa (S3), Nyssa sylvatica (S3), Quercus palustris (S3), Carex swanii (S3), Carex squarrosa (S2), and Desmodium rotundifolium (S2). Interestingly, especially given its predilection for successional habitats, round-leaved greenbrier was noted as being associated with old-growth Nyssa sylvatica at Site 8 (Paul O’Hara s.n. specimen data--HAM16237).

According to Nova Scotia Department of Natural Resources biologist M.F. Elderkin, the round-leaved greenbrier population in Nova Scotia is confined mostly to lakeshores in the southwest where it shares a distribution characteristic of many other plants in the Atlantic coastal plain (M.F. Elderkin, pers. comm. 2006).

Habitat trends

In Ontario, with the exception of a portion of the woodlots at Sites 5 and 13, the main habitats present during the preparation of the 1994 report appear to be extant (specific habitat characteristics may have changed).

That fact notwithstanding, this species is under considerable threat from habitat development, especially in Essex County, where it is confined to scattered small isolated woodlots, surrounded by inhospitable agricultural settings. Furthermore, woodlot blocks, while extant, are not necessarily still suitable for this species. For example, Site 4, which fieldworkers were not permitted to access in 2006, is likely highly impacted (from the perspective of round-leaved greenbrier) by the conversion of half of the woodlot into a fenced “deer enclosure.” Regardless of the specifics of the habitat alteration, high densities of deer threaten round-leaved greenbrier survival.

In Niagara, where the pool of potential habitat is larger, the development pressures are probably even greater than they are in Essex. One population there (Site 13) is the site of an active development proposal (an 83-unit development), and another (Site 7) persists in a woodlot remnant adjacent to a major suburb. All sites (with the possible exception of Site 12, which is in a city park) in Niagara are at risk of development pressures including the proposed “Niagara to GTA Corridor.” Site 12 itself was historically at least twice its current size; it was divided for roadway construction and residential development (Garofalo pers. comm. 2006).

Some losses had already been documented during the preparation of Ambrose’s 1994 status assessment. He notes that “although more sites are now known than before, current habitat loss in Niagara Region appears to be causing a pronounced recent decline in the range of this species (G. Meyers, pers. comm.). The loss of one known habitat has also been documented in Essex County (M. Oldham, pers. comm.).”

No specific information was compiled on habitat trends in Nova Scotia in view of the relatively stable populations in the province and the limited threats to the species.

Habitat protection/ownership

In Ontario, the majority of sites are in private ownership, with the exception of:

  • Portions of Site 6, which are owned by the Long Point Region Conservation Authority.
  • Site 12, which is in a city park in Welland; and possibly
  • Portions of Site 1 (listed as property of the Essex Region Conservation Authority in Ambrose 1994, but this statement was contradicted in conversation with ERCA staff in 2006).

No detailed information has been compiled on habitat protection and ownership in Nova Scotia since the species is not tracked by the province or the Atlantic Canada Conservation Data Centre. However, some of the populations are known to occur in protected areas such as Kejimkujik National Park and the Tobeac Wilderness Area.

Page details

Date modified: