Swamp rose-mallow (Hibiscus moscheutos) COSEWIC assessment and status report: chapter 5
Habitat
Habitat Requirements
In its prime range, Hibiscus moscheutos occurs as a prevalent species in the oligohaline portions of estuaries, typically in low-salinity and freshwater marshes along the east coast of the United States, but also dominates marshes with highly restricted tidal regimes and often forms monospecific stands (Cahoon & Stevenson, 1986).
In Canada, H. moscheutos is largely restricted to the Carolinian or Deciduous Forest Region. However, recent discoveries in central and eastern Lake Ontario have extended the range of this species into the Great Lakes – St. Lawrence forest region. All populations are confined to early successional wetlands that are associated with or have had a recent association with Lakes Erie, Ontario, or St. Clair. The species is most common in two types of wetlands: in deep-water Typha marsh, where it occurs along the interface with the open water in the cattail mat; and meadow marsh (see Figure 4). These wetland types are dominated, respectively, at the Hibiscus stations, by Typha X glauca and Phragmites australis, unless the meadow marsh is flooded periodically. Hibiscus moscheutos is also found in open wet woods, thickets, spoil banks, and drainage ditches. It never spreads ‘unassisted’ farther than a few hundred metres from the Great Lakes or their associated wetlands, and populations recorded inland at Kingsville, St. Thomas, and Welland, are believed to have been introduced with landfill.
The importance of water-level fluctuations in maintaining marsh habitat has been well documented in the literature (e.g., Harris & Marshall, 1963; Van der Valk & Davis, 1978; Keddy & Reznicek, 1982) with drawdowns used as a standard management technique. The favourable impact of drawdowns on a Lake Erie population of H. moscheutos was described by Farney and Bookout (1982), who found that plants flourished during periods of low water levels. Indeed, the two most prolific populations in Ontario, at site #8 and site # 39 are both thriving in shoreline dyked marshes with frequent drawdowns and little evident competition. Historically, populations of Hibiscus would have been maintained in early successional coastal habitats by natural fire, storms, and beaver activity. For the past 100 years natural fire has been actively suppressed in southern Ontario, and only in the last 25 years has prescribed burning been implemented. This burning has been restricted to a few selected high priority sites, with every attention devoted to coastal marsh habitats. Beaver have been extirpated from Essex County and the Municipality of Chatham-Kent for decades. Various forms of anthropogenic disturbance also serve to maintain or create open conditions, well illustrated by several populations thriving in micro-wetlands along railway verges. Rose-mallow is thus tolerant of both disturbance and unstable substrates. Water-level fluctuations that periodically expose and then re-flood, thus controlling Phragmites, shrubs, and small trees, are probably critical for the long-term suvival of this species in Canada.
Apart from dyked marshes, H. moscheutos seems to prefer coastal marshes that are protected by a barrier beach, e.g. Point Pelee and Rondeau, rather than those exposed to the open water, i.e. the marshes associated with the spit of Long Point. Even at Long Point, the two extant populations are both at the base of the spit, in marshes protected by barrier beach. The species does not seem to thrive in the high levels of natural disturbance experienced in marsh habitats open to the lake. Of interest in this regard, is the fact that Reznicek (pers. comm. 1985) has noted that plants on Long Point appeared to flower poorly and usually later in the season than their counterparts in Essex County.
Stuckey (1968) suggested that Hibiscus laevis may be adversely affected by pollution, and this certainly appears to be the case with H. moscheutos as well. Its prime coastal wetland habitat, nested in the agricultural and industrial fabric of southwestern Ontario, is subjected to high inputs of nutrients, herbicides, pesticides, and heavy metals.
A direct apparent impact of this degrading habitat on Hibiscus, has been the rise of Phragmites, which is exploiting the artificially high nutrients entering the system. Phragmites likely out-competes Hibiscus in this altered environment, unless periodic flooding occurs. A similar situation has likely occurred with Typha X glauca.
Figure 4. Habitat of Hibiscus moscheutos at Willowood East.
The soils associated with H. moscheutos are organic or clay, of medium texture and usually moist throughout the spring and summer. Soils have a circumneutral pH with high levels of exchangeable Ca, K, P, and Mg. In all ten study sites, concentrations of exchangeable cations decreased in the order of Ca> Mg> K> P (see Table 1 in original report). Despite the abundance of H. moscheutos in the coastal marshes of the mid-Atlantic states, this plant is not a halophyte (plants of seashore or of alkaline soils). Its widespread occurrence on the Great Lakes precludes any suggestion of a dependence on salt for growth.
Narrow-leaved emergents are the most common associates of Swamp Rose- Mallow. Other than Typha X glauca and Phragmites australis, the most commonly associated graminoids include: Phalaris arundinacea, Calamagrostis canadensis, Eleocharis erythropoda, Scirpus fluviatilis, Typha latifolia, Sparganium eurycarpum, Carex stricta, and Carex lacustris. Frequently associated herbs are: Polygonum amphibium, Impatiens capensis, Sagittaria latifolia, Calystegia sepium, Scutellaria galericulata, Iris virginica, Eupatorium perfoliatum, Lycopus americanus, Asclepias incarnata, Solidago altissima, Polygonum lapathifolium, Sium suave, Butomus umbellatus, Nuphar advena, and Lythrum salicaria. Cornus racemosa, Salix spp., Vitis riparia, Cephalanthus occidentalis, and seedlings and saplings of Populus deltoides, were often found in and adjacent to stands of rose-mallow, and occasionally Decodon verticillatus.
A few of the species associated with H. moscheutos are considered rare in Ontario (Oldham, 1999). These are Rosa setigera (Ruscom Shores), Agrimonia parviflora (Ruscom Shores), Nelumbo lutea (sites # 3, 4, 37, 39), Platanthera leucophaea (site # 7), and Lythrum alatum (site # 5). Platanthera leucophaea has been accorded official COSEWIC status as Endangered in Canada, while Rosa setigera has been given official status as Special Concern in Canada. Although not directly associated with H. moscheutos, the vulnerable (S3) Vernonia missurica (sites # 7 and 21) and imperiled (S2) Gaura biennis (site # 7) were found nearby.
Trends
The major coastal marshes that support Hibiscus are quite secure, either as protected parks, e.g. sites #26, and 42; private hunt clubs, e.g. site #39; or First Nation Lands which are leased out for waterfowl hunting with substantial financial remuneration. There is thus little chance that these marshes will be converted to other uses, and none of the major marshes have been developed since the original status report. Many are also identified as provincially significant wetland, and are thus protected under the Provincial Policy Statement on Wetlands. There is a trend toward loss of the smaller wetlands, through development of subdivisions and single estate lots, and impacts associated with proximity to such housing (sites #7, 15, 25), the south shore of Lake St. Clair, e.g. at sites # 17, 19, 20; and to a lesser extent incursions by agricultural land, e.g. at site # 20.
The most noticeable trend with Hibiscus, is with the loss of suitable habitat through exclusion by Phragmites, and to a lesser extent, competition by Typha X glauca. These two invasives were not even noted as “Threats to Survival” by Ford when surveying for the original status report in 1985, but were obvious in a number of the sites surveyed by Allen in 2002. Coastal marshes on the southern shore of Lake St. Clair, at sites # 17, 19, 21, 23; on the Lake Erie Shore at Fox Creek Conservation Area (where Hibiscus is now seemingly absent); along the shores of the Detroit River and the Canard River; and in the Big Creek system; are virtually solid seas of Phragmites, with little else other than some Lythrum salicaria, Typha X glauca, and young cottonwood growing there. Typha X glauca was noted as co-dominant with Phragmites in the Big Creek system. It is dominant along the banks of Cedar Creek; at site # 27; the stations in the St. Clair Marshes; and has been out-competing the Hibiscus at site # 39 over the last few years (Haggeman, pers. comm. 2002).
Protection/Ownership
Of the 51 extant stations for Hibiscus moscheutos, the ownership breakdown is as follows:
- 23 are privately owned by single or multiple landowners;
- 14 are publicly owned by government conservation organizations, either as 6 provincial parks (sites # 1, 51, 31, 33, and 42); 5 Conservation Authority properties (sites # 4, 7, 21, 23, and 28); 2 National Park (sites 26 and 32); or 2 National Wildlife Area managed by the Canadian Wildlife Service (sites 37 and 49).
- 5 are publicly owned by municipalities, one of which is managed as an urban park, with the other five on right-of-ways.
- 4 are owned by Canadian National Railways, and exist along the right-of-ways.
- 2 are owned by First Nations, both by Walpole First Nation.
- 1 is owned by the provincial Ministry of Transportation (site # 46).
- 1 is split between public and private ownership (site # 10).
- 1 is unknown ownership (Duck Island).
Most populations of Hibiscus moscheutos occur on private land and in ditches on railway rights-of-way. These include the largest populations in the province (sites # 8 and 39), and substantial ones, such as at sites #20 and 12. However, large populations also occur on land owned by the federal government (sites # 26, 37, and 49), the provincial government (sites # 31 and 42) and the Essex Region Conservation Authority (site # 4, and portions of sites # 12 and 49). A total of eleven stations are known to occur in dyked marshes, four of which are publicly owned (sites # 4, 37, 49, and 50). Active protection or management specifically directed towards H. moscheutos is not known to occur on any private land.
A number of the stations are recognized as provincially significant wetlands, including several of the private sites (sites # 3, 8, 12, 15, 38, 39), and all of the Big Creek populations (sites # 27, 30, 41). As such, these stations are to be afforded protection as Category 1 within the Provincial Policy Statement for Ontario (PPS). The PPS states that, “Development and site alteration will not be permitted in significant wetlands south and east of the Canadian Shield.” (Ontario Government, 1997). As required by the Planning Act, local planning authorities “shall have regard to” policy statements issued under the Act. Providing that the private lands supporting the Hibiscus populations do not have planning approvals prior to 1993, these sites should not be developed. The populations along the railway rights-of-way would likely not be classified as provincially significant wetland.
Of the 20 stations believed to be extirpated, 11 are private, 7 are public, 1 is First Nation, and 1 of unknown ownership. Of the seven public sites, one is a provincial park (Lighthouse Point Nature Reserve on Pelee Island), one is a National Wildlife Area (Long Point), one is a conservation authority property (Fox Creek), one is an urban park (Mitchell’s Bay), and three are municipally owned (Kingsville Sewage Lagoon, West Dock at Pelee Island, and the right-of-way 5.3 km east of Oxley in the Town of Essex).