Wood-poppy (Stylophorum diphyllum) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Stylophorum diphyllum is typically a plant of rich forests. Habitat information on herbarium specimens collected throughout its range includes species-rich woods, forested ravines and slopes, woodland streams, ravine bottoms and bases of bluffs. Most collections appear to be from ravines and slopes, but this may be an artefact of the distribution patterns of remnant woodlots on land unsuitable for agriculture. More specific habitat annotations providing information on edaphic conditions includes "rich damp beech woods", "rich limestone woods", "limestone slopes and terraces", "moist rich woods", "mesic slopes" and "loamy sand beech-maple woods". Additional descriptions provided by Kiger (1997) include thickets, cedar barrens, shaded dunes and occasionally in fields, often on slopes, in loam or sand.

In Ontario all three sites are in rich, mesic, mixed deciduous woodland on calcareous glacial till deposits of loamy clay. Two sites (London and Fanshawe) are on the slopes of the Thames River, while the third (Ilderton) is on a level till plain well away from any water-course. At London and Ilderton outlying plants are present on disturbed areas (fill and drainage spoils respectively) adjacent to the main population. In natural settings Stylophorum diphyllum usually grows in full shade, but cultivated plants flourish in partial sun (personal observation). Habitat that appears suitable for Stylophorum diphyllum appears to be much more widespread and extensive, even locally, than the species itself.

The canopy trees at the Ontario populations of Stylophorum diphyllum include sugar maple (Acer saccharum), white ash (Fraxinus americana), American beech (Fagus grandifolia), black cherry (Prunus serotina) and hackberry (Celtis occidentalis). The largest trees are about 40 cm diameter at breast height. The shrub layer is open to closed, predominantly choke cherry (Prunus virginiana) and saplings of the canopy trees. Where it exists, Stylophorum diphyllum often forms the dominant groundcover species, the closest neighbour to it tending to be other Stylophorum diphyllum individuals. Otherwise, associated ground layer species include many of the normal suite of rich woodland species such as blue cohosh (Caulophyllum thalictroides), Virginia waterleaf (Hydrophyllum virginianum), Canada waterleaf (H. canadense), yellow trout-lily (Erythronium americanum), wild ginger (Asarum canadense), zigzag goldenrod (Solidago flexicaulis), bottle-brush grass (Elymus hystrix), spotted jewel-weed (Impatiens capensis), false Solomon’s seal (Maianthemum racemosum) and Jack-in-the-pulpit (Arisaema triphyllum). The exotic invasive species garlic mustard (Alliaria petiolata) is also present at two sites (Bowles, unpublished data).

Habitat trends 

Heavy logging followed by burial by fill at the London site reduced a large section of the known habitat of Stylophorum diphyllum in 1993. Since then the remnant population has expanded slightly. Erosion and deposition in the creek valley and at the edge of the fill affects local outlying individuals during some storm events. Opening of the canopy by logging and the death of trees affected by fill operations has been followed by dense growth of saplings. It is unclear what the overall effects of these changes in canopy cover have been.

At Fanshawe, many of the trees around the Stylophorum diphyllum site have died in the last 5 years. This has created both openings in the canopy and a considerable amount of coarse woody debris. Understorey shrub growth (mainly Prunus virginiana) has increased and may be shading out the original stand. Alliaria petiolata is abundant at this site, but it appears to have diminished slightly in the immediate area of the Stylophorum diphyllumpossibly due to mitigating actions to remove rosettes of the invasive near the wood-poppy plants. These changes in the habitat may also have affected seed predator (mice) and disperser (ant) populations, shade, competition, soil processes and mycorrhizae. In the last two years recruitment has suddenly increased at this site.

At Ilderton the population is at the edge of an active sugar bush. Apart from construction of an adjacent municipal drain the site management has changed very little over the last 30 years. The drain spoil has created recruitment sites for Stylophorum diphyllum.

Habitat protection/ownership 

The London and Ilderton sites are privately owned. The London site is within the 30-year growth boundary for the City of London and development is occurring in the neighbourhood. A Community Plan is being prepared for the area that must provide some degree of setback to protect the population. However, the presence of residential development in the area is likely to lead to increased disturbance and recreation pressure at this site as well as to a potential increase in exotic competitors.

The Ilderton site is part of a large, well established commercial sugar bush operation. The landowners are aware that Stylophorum diphyllum is present and have no plans at present for any land use change that might affect the population. Management and construction operations on the drain could affect some plants.

The Fanshawe population is in a Conservation Area owned and managed by Upper Thames River Conservation Authority (UTRCA). The Conservation Authority is aware of the presence of Stylophorum diphyllum on the property and has managed the site to help protect the plants by re-routing a trail and installing signage.

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