Swamp rose-mallow (Hibiscus moscheutos) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

For this report, the term population is used to refer to the basic unit, and is defined as, “A group of individuals that reproduce with one another and produce offspring” (Primack 1993). This term, when applied to Hibiscus moscheutos, does not imply any genetic isolation between populations, as the species likely experiences few barriers to genetic exchange between proximal populations in southern Ontario, other than of course, the fragmentation of its prime habitat. The term station, site, or population, is thus used interchangeably to refer to one or more subpopulations of H. moscheutos that are separated from other populations by at least 1 km of unoccupied or unsuitable habitat. This is the definition used by the Natural Heritage Information Centre (NHIC) for an Element Occurrence (EO), thereby facilitating comparisons with, and additions to, that dataset. All populations were plotted on topographical maps in NAD 27, using the information collected by the first author, e.g. pers. comm., and referencing these against the NHIC Element Occurrence Summaries for each population. The criteria regarding ‘lumping’ or ‘splitting’ to define a population was then applied, with those records within one km proximity treated as subpopulations.

There are 51 extant stations for Hibiscus moscheutos in Canada, compared with 40 documented for the original status report. Hibiscus moscheutos varied from an infrequent component at a station, with only a few ramets (vegetative stems with the potential for independent existence), to the dominant species, with hundreds of genets (a plant that originates from a seed) and thousands of flowering ramets present. A common root system in a dense clump of 1-2 metres in diameter can support up to 70 flowering stems, and these clumps are usually randomly distributed throughout a given habitat, and appear to persist for some time. The problem in population estimates with the species lies in the fact that it is impossible to distinguish between old fragmented clumps and young plants. As a result, most of the population estimates by various observers have focussed on the number of flowering stems, while some have noted the number of individual clumps. Crude estimates of population sizes, using stem counts, were obtained during the 2002 field surveys, and these are cited in Table 1, along with any prior quantitative observations, including in particular, Ford’s 1985 surveys. Those populations believed to be extirpated are also listed with their respective population estimates, for comparative purposes.

A total of 71 stations has been recorded for Hibiscus moscheutos; 20 of which are now believed to be extirpated; two are considered as historical populations of unknown status. Of the 51 extant stations, 47 have been recorded with some level of quantification (Table 1). Of these 47 stations, 19 of these are believed to support moderate to large populations of 100 clumps or stems. The majority of sites (28 localities), consist of small populations, many with only single or few plants. Of the 19 moderate to large stations, only four (#8, 39, 26, 42) can be said to be common over an extensive area, and only at the former two does Hibiscus form a continuous cover. Population #8 has the largest number of plants, estimated at 10,000 flowering stems over approximately 30 hectares of dyked meadow marsh. The actual number of plants represented by this count of stems is unknown but likely represents >1000 plants. Population #39 has the next highest number of stems and also consists of >1000 plants scattered over approximately 18 hectares of dyked meadow marsh. At population #26, Hibiscus is locally common in the open marsh with hundreds of clumps along the margin of the cattail mat (Oldham pers. comm. 2002). The species is also common at population #42, with perhaps 100 clumps scattered for several kms along the open edge of the marsh (pers. comm. Dobbyn, Oldham, & Woodliffe, 2002). Although some of the stations support high numbers of plants, the actual area of occupancy is very small. Both population #20 and #7 boast 1,000 stems each; the former exists in ditches wedged between railway tracks and roadways, while the thousands of flowering stems at #7 are packed into a section of meadow-marsh of less than one hectare.

Table 1. Hibiscus moscheutos Population Information for Ontario Stations.
[updated with Aug/Sept. 2003 field observations for several sites by A. Woodliffe and M. Austen].
 Pop#/
Site
Name
Number of
Plants/
Flowering
Stems
<1980s
Number of
Plants/
Flowering
Stems
1980s
Number of
Plants/
Flowering
Stems
1990s
Number of
Plants/
Flowering
Stems
2000s
Observer(s)
or Rationale
#1 1 plant 2 plants 1 plant 0
  • Stewart 1964 & 68
  • Oldham 1989
  • Oldham 1999
  • Allen & Jean 2002 –
  • not located
#2       1 plant
  • Woodliffe 2001
#3   Few plants Many plants 0
  • Ford 1985
  • Reume 1999
  • Allen 2002
  • Different sub-pops
#4   70 stems   Local & occas.
  • Ford 1985
  • Allen & Waldron 2002
#5   No est.    
  • Ford 1985
#6   >400 stems; scattered plants   Few plants; 30 stems
  • Ford 1985
  • Oldham 1987
  • Allen 2002
  • Different sub-pops
#7   2,000-3,000 stems   1000s of stems
  • Ford 1985
  • Allen 2002
#8   2,000-3,000 stems   10,000 stems (>1000 plants)
  • Ford 1985
  • Allen 2002
#9   7 stems    
  • Allen 2002
#10       scattered
  • Allen & Waldron 2002
#11       scattered
  • Allen 2002
#12   300 stems   20 stems
  • Ford 1985
  • Allen 2002 –
  • not a full survey
#13   3 stems    
  • Ford 1985
#14   1 clump    
  • Oldham 1987
  • Could not access Allen 2002
#15   5-10 clumps   225 plants
  • Oldham 1987
  • Larson 2000
#16   1 clump   1 clump
  • Oldham 1985
  • Allen 2002
#17   Large colony   150 stems
  • Oldham 1985
  • Allen 2002
  • Different sub-pops
#18   1,000 stems    
  • Ford 1985
#19   800 stems   100 stems
  • Ford 1985
  • Allen 2002
#20   Few stems   1,000 stems
  • Ford 1985
  • Allen 2002
#21   200 stems    
  • Ford 1985
#22       No est.
  • Haggeman 2002
#23   1 clump    
  • Oldham 1985
#24   1 clump    
  • Oldham et al. 1988
#25   Local Few plants 30 stems
  • Oldham 1988
  • Oldham 1990
  • Allen 2002
#26   Scattered   100s of clumps
  • Ford 1985
  • Oldham 2002
#27   300 stems   200-300 stems
  • Ford 1985
  • Allen 2002
#28   10 stems    
  • Ford 2002
#29   Few; 5-10
clumps;
uncommon
  none
  • Oldham 1982
  • Oldham 1985
  • Oldham 1988
  • Woodliffe, Aug.. 2003
#30   1clump; 10-20
clumps
  none
  • Oldham 1982
  • Oldham 1985
  • Woodliffe, Aug. 2003
#31 1 colony Few; rare 1 clump 29 clumps
  • Stuckey 1967
  • Oldham 1982
  • Oldham 1988
  • Oldham 1999
  • Woodliffe Aug. 2003
#32        
  • No estimates of #s
#33   7-8 clumps    
  • Oldham 1988
#34   10 stems    
  • Ford & Allen 1985
#35   1 clump   1 clump
  • Oldham et al. 1985
  • Woodliffe, Aug. 2003
#36   5 stems    
  • Ford 1985
#37   150 stems;
30 stems
  140+ stems
  • Ford 1985
  • Oldham 1987
  • Allen et al. 2002
#38   300 stems   Scattered clumps
  • Ford 1985
  • Allen et al. 2002
  • different sub-pops
#39       1000s of stems
(>> 1000 plants)
  • Allen et al. 2002
#40       Dozens of plants
  • Haggeman 2002
#41   Few stems   Scattered clumps;
340 clumps
  • Ford 1985
  • Woodliffe 2000
  • Woodliffe, Sept. 2003
#42       Common;
50-100 clumps;
75 clumps
Likely >500 clumps
  • Dobbyn 2002
  • Oldham 2002
  • Woodliffe, Sept. 2003
#43       1 clump
  • Woodliffe 2002
#44   Several small pops    
  • Allen et al. 1985/86
#45       1 patch running for 100 metres
  • Austen 2003
#46   20 clumps    
  • Meyers early 1990s
#47   6 plants    
  • Meyers early 1990s
#48       Large group of plants
  • Thompson & Smith
#49   2 plants, many stems 171 stems 500 stems
  • Reznicek & Catling 1981
  • Sutherland 1992
  • Allen & Jean 2002
#50   50 stems; 1 clump   3 clumps
  • Ford 1985
  • Oldham 1987
  • Bowles & Gorniak 2002
#51     4 plants with 14 stems 8-9 plants with 46 stems
  • Brownell 1998
  • Bree 2002
#52        
  • No estimates of #s
#53 Few plants Scarce   1 clump
  • Stuckey 1969
  • Oldham 1983
  • Woodliffe, Aug. 2003
Fighting Island   100 stems   0
  • Ford 1985
  • Believed extirpated – Allen 2002
LaSalle Marina   40 stems   0
  • Ford 1985
  • Believed extirpated – Allen 2002
Kingsville Sewage Lagoon   Few clumps; extirpated   Extirpated
  • Oldham 1983
  • Ford 1985
  • Allen 2002
Fox Creek Cons. Area   1 clump   0
  • Believed extirpated – Allen 2002
1.5 kms S of Arner   50 stems   0
  • Believed extirpated – Allen 2002. A subpop of Cedar Creek station.
4.5 km E of Oxley   50 stems   0
  • Believed extirpated – Allen 2002
5.3 km E of Oxley   1 plant   0
  • Believed extirpated – Allen 2002
S of West Pump Few plants Scarce    
  • Stuckey 1969
  • Oldham 1983
Turkey Point Marsh No estimate   0  
  • Norris 1943
  • Bowles 198?
  • Believed extirpated
Bluff Point, Long Point   No estimate    
  • Catling 1981
  • Believed extirpated
Thames River Mouth No estimate      
  • Stock 1956
  • Believed extirpated
Mitchell’s Bay   1 plant    
  • Oldham 1987
  • Believed extirpated
Sarnia No estimate 0    
  • Dearness 1894
  • Ford 1985
  • Believed extirpated
Grassy Bend Island, Walpole No estimate      
  • Shields 1950
  • Believed extirpated
Welland Canal Few plants 0    
  • Anderson 1952
  • Ford 1985
  • Believed extirpated
Niagara-on-the-Lake No estimate 0    
  • Scott 1910
  • Ford 1985
  • Believed extirpated
Queenston No estimate 0    
  • Scott 1899
  • Ford 1985
  • Believed extirpated
Miller Creek Large patch      
  • Sherk 1968
  • Believed extirpated

Although many stations have been known for over 50 years, it is difficult to determine whether populations have been declining or fluctuating in numbers over this time period. This is largely due to the fact that prior to 1985, quantitative data was gathered at only three stations. Compounding this situation is the lack of confidence that population estimates are applicable to the same sub-populations within a given station. In the 17 years between Ford’s field surveys in 1985 and Allen’s in 2002, stations seem to have remained relatively stable in their numbers. One of the main differences is that seven populations and four subpopulations documented by Ford are now believed extirpated, however all but two of these (Fighting Island and Puce) are small populations. Although not verified at this time, the senior author, based on his 2002 field observations, believes that some of the stations are in decline as a result of competition with Phragmites, and to a lesser extent Typha X glauca, e.g., the populations on the Detroit River, those at #3, #9, #12, #50, as well as those populations along the south shore of Lake St. Clair at #17, #18, #19, #16, #21.

A total of 19 stations listed in the present report as extant were either not listed at all in the original report, or were cited as Historical Populations of Unknown Status. The majority of these were not discovered until after the original report was completed, mostly in the late 1980s, but some very recently, e.g. site #51 (1998), site # 2 (2001), site # 22 (2002), and site # 40 (2002). While site # 51 almost certainly represents a new population, those at sites 22, 39, and 40 are in privately held marshes with regulated access, and could have thus escaped detection for some time. Similarly, sites # 32 and 33 are quite remote, and the populations here may have existed for several years prior to the first recorded observations in the late 1980s.

Ford listed 17 stations as “Historical populations of unknown status”. Although some of these were noted as possibly extirpated, none were officially cited as such. The present report serves to clear up the uncertainly with these stations, retaining only two stations as “Historical” (Mitchell’s Bay and Long Point Spit); with ten stations being moved to “Extirpated”, three to “Extant”, and the Pelee Island Fox Pond station being combined with Fish Point. Of the 20 stations now listed as extirpated, most are small populations, the rest were never recorded with abundance information.

About 51 extant stations have been documented comprising a total of about 25,000 flowering stems. The total number of actual plants represented by such an estimate is uncertain but likely represents thousands of plants (but < 10,000). The total area of occupancy is estimated at about 9.5 km², and the total extent of occurrence for the 51 stations is about 22,000 km².

All populations visited during 1985 and 2002 appeared vigorous and flowered successfully. However, Reznicek (pers. comm. 1985) has noted that plants on Long Point (site # 50) appeared to flower poorly and usually later in the season than their counterparts in Essex County. It would appear that if habitat requirements are maintained, populations are able to persist for a considerable period of time.

In Ontario, Hibiscus moscheutos is not under immediate threat for the time being. It is fairly common in Essex County, and in the Municipality of Chatham-Kent along the Lake St. Clair shoreline, and large populations of thousands of flowering stems persist, albeit primarily in the artificial conditions afforded by dyked marshes. In natural marsh habitats, its success has been challenged by the recent rise of Phragmites australis, and to a lesser extent Typha X glauca, and a downward trend in these non-manipulated sites seems inevitable.

Extirpated Populations

Essex County

Fighting Island, Town of LaSalle (formerly Sandwich West Township) (EO 014). Last observed in 1985 by B.A. Ford. The island was not accessed by G.M. Allen in 2002 but the island was scanned 12 August 2002 by binoculars from the same vantage point as Ford’s observation, from the river’s edge at the LaSalle Marina toward the northeast end of the island, but no Hibiscus was observed. Virtually all marsh habitat observed was occupied by Phragmites and the station is believed to be extirpated.

LaSalle Marina, Town of LaSalle (formerly Sandwich West Township) (EO 048). Last observed in 1985 by B.A. Ford as a “Large clump of 40 flowering stems along edge of cattails adjacent to dredged channel.” This population could not be relocated in 2002 by G.M. Allen. The dock 200 metres to the south was also searched, but both shorelines are in residential development and any available marsh remnants are dominated by Phragmites.

Kingsville Sewage Lagoon, Town of Kingsville (formerly Gosfield South Township) (EO061). Observed by M.J. Oldham in 1983 with ”A few clumps.” Ford noted that by 1985 “This population appears to have been extirpated as the result of sewage pond construction.” G.M. Allen again searched this site 12 August 2002. No natural wetland was observed, and the water levels were very high in the settling ponds. The pond edges, which can sometimes offer suitable wetland habitat, mostly maintained as rock gabion. Last observation 1983, no suitable habitat exists, and believed extirpated.

Fox Creek Conservation Area, Town of Essex (formerly Colchester South Township) (EO 041). Observed in 1985 by Ford with “Single plant growing in a low area adjacent to a parking lot.” Not refound by Allen in 2002, and essentially all available habitat occupied by Phragmites on east side of road. West of the road was checked out as well, with no Hibiscus observed. Last observation by B.A. Ford in 1985.

Cedar Creek, 1.5 km south of Arner, Town of Kingsville (formerly Gosfield South Township) (Technically one of the subpopulations of the main Cedar Creek station). Ford observed “About 50 flowering stems growing along County Road 23 adjacent to cornfield with Phalaris arundinacea and Scirpus fluviatilis.” in 1985. This population could not be located by G.M. Allen on 12 August 2002 and is believed to be extirpated.

4.5 kms east of Oxley (not listed on NHIC EO Summary), Town of Essex (formerly Colchester South Township). Last observation in 1985 by B.A. Ford. Species could not be refound in 2002 by G.M. Allen but entire habitat not investigated.

5.3 km east of Oxley, at the junction of County Roads 23 and 50 (not listed on NHIC EO Summary), Town of Essex (formerly Colchester South Township). Last observed by B.A. Ford in 1985 as “Single plant growing in ditch.” Not refound in 2002 by G.M. Allen.

0.5 km south of West Pump, West Shore Road, Pelee Island (EO 003). First observation in 1959 by Armstrong, then in 1969 by R. Stuckey as “A few plants.”, and subsequently by M.J. Oldham in 1983 as “Ditch, scarce”. Not observed since and believed extirpated.

Population #30 (EO 004) - Middle Point Woods, Pelee Island. Observed in 1985 by M.J. Oldham with, “Ten to twenty clumps in low wet opening of woods.” [none present when observed by Woodliffe in Aug. 2003].

Population #29 (EO 005) – Lighthouse Point, Pelee Island. Last observed by M.J. Oldham in 1988 as “uncommon.” [none seen by Woodliffe in Aug. 2003]

Norfolk County

Turkey Point Marsh, Delhi Township (EO 021). Not recorded since 1943 when collected by T. Norris, and not found despite intensive coverage by J. Bowles in the late 1980s as part of a detailed ANSI inventory. Considered extirpated.

Bluff Point, Long Point National Wildlife Area, Norfolk Township (EO 018). Last recorded in 1981 by P.M. Catling near tip (on north side) of Long Point. This population has not been observed in recent years and is believed extirpated (Ashley, pers. comm. 2002). Photo by P. Mohr at MICH. Publicly owned by Environment Canada.

Municipality of Chatham-Kent

Municipality of Chatham-Kent/Essex County Line, Lake St. Clair (EO 017). Last observed in 1956 by L.L. Stock. This station was searched in 2002 by G.M. Allen by scanning with binoculars from the south side of the Thames River at Lighthouse Cove. No Hibiscus was located, and the entire marsh viewed was occupied by Phragmites, two cabins, manicured lawns, and steel retaining walls. Considered extirpated.

Mitchell’s Bay, Lake St. Clair, Dover Township (EO 029). Last observed in 1987 by M.J. Oldham with “Single vegetative plant on disturbed beach at park”. Publicly owned as a municipal park and believed to no longer be present (Haggeman, pers. comm. 2003).

Lambton County

Grand Trunk Railway at Sarnia, Lake St. Clair. Last observed in 1894 by J. Dearness. Ford noted in 1986 that “The development of wetland habitat for industrial use has probably extirpated H. moscheutos from this station.”

Grassy Bend Islands, Walpole Island First Nation (EO 056). Last observed in 1950 by J.K. Shields with no abundance information available. This station was not searched in 2002 by G.M. Allen but it has not been observed in over 50 years and is probably extirpated.

Niagara RM

Along the Welland Canal, City of Welland (EO 033). Last recorded in 1952 by Anderson with “a few plants” noted. Ford noted in 1985 that this population could not be relocated by him and that development of wetland habitat for industrial and recreational use had probably extirpated the Hibiscus from the site. Not resurveyed by G.M. Allen in 2002.

Niagara-On-The-Lake, Town of Niagara-On-The-Lake. Last observed in 1910 by Scott. Available information very vague. Ford noted in 1985 that this population could not be relocated by him and that development of wetland habitat for industrial and recreational use had probably extirpated the Hibiscus from the site. Not resurveyed by G.M. Allen in 2002.

Queenston, Town of Niagara-On-The-Lake. Last recorded in 1899 by Scott. Available information very vague. Ford noted in 1985 that this population could not be relocated by him and that development of wetland habitat for industrial and recreational use had probably extirpated the Hibiscus from the site. Not resurveyed by G.M. Allen in 2002.

Miller Creek, Bertie Township. Not recorded since 1968 when observed by L.C. Sherk as “Large patch 20 by 10 feet.” Location data obscure. Not resurveyed by G.M. Allen in 2002.

Historical Populations of Unknown Status

Municipality of Chatham-Kent

Mitchell’s Bay, Lake St. Clair, Dover Township, 4 km SSW of Mitchell Bay (EO 027). Last observed in1950 by J.K. Shields. Good shoreline marsh habitat certainly exists in this location between those stations at Patrick’s Cove and St. Luke’s Bay, and the species is believed to still be in the vicinity (Haggeman, pers. comm 2003).

Potential Sites for Investigation

The Canadian range of H. moscheutos has been intensively surveyed by many botanists. Due to the conspicuous nature of this plant when it is in flower, the localities cited in this report probably represent a high proportion of this species' actual occurrence in Canada. Continued searching, however, may reveal new populations within its known range. Two potentially new stations are:

Possible site in Malden Township 2 km southeast of Amherstburg, at very north end of Big Creek Marsh, suggested by G.E. Waldron, was investigated 11 August 2002 by G.M. Allen but no Hibiscus was observed by scanning with binoculars to the north and south. Marsh habitat is available north and south of the bridge over Big Creek, but is very choked with Phragmites.

The interior marshes of Big Creek (Amherstburg) certainly warrant investigation by boat for stands of Hibiscus. This expansive wetland was only surveyed by road for the update. Good habitat with few stations ever documented exists between County Road 20 and Holiday Beach Conservation Area.

Also in 2002 G.M. Allen surveyed unsuccessfully in Anderdon Township 2 km east of River Canard at the bridge over the Canard River. Once again, every available marsh habitat scanned by binoculars looking to the north and south along the river was occupied by Phragmites.

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