American water-willow (Justicia americana) recovery strategy: chapter 2

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1. Background

• 1.1 Species assessment information from COSEWIC
• 1.2 Description
• 1.3 Population and distribution
  • 1.3.1 Global range and range in Canada
  • 1.3.2 Population size and trends
• 1.4 The needs of American Water-willow
  • 1.4.1 Biological and habitat needs
  • 1.4.2 Limiting factors
• 1.5 Threat identification
  • 1.5.2 Description of threats
    • 1.5.2.1 Changes to water regimes
    • 1.5.2.2 Erosion
    • 1.5.2.3 Alien invasive species
    • 1.5.2.4 Trampling by hunters, canoeists and kayakers
    • 1.5.2.5 Infilling
    • 1.5.2.6 Grazing by wild animals
    • 1.5.2.7 Degradation of water quality
• 1.6 Actions already completed or underway
• 1.7 Additional American Water-willow information requirements

1.1 Species assessment information from COSEWIC

Date of Assessment: May 2000

Common Name (population): American Water-willow

Scientific Name: Justicia americana

Committee on the Status of Endangered Wildlife in Canada (COSEWIC) Status: Threatened

Reason for Designation: This clonal aquatic plant inhabiting the shorelines of lakes and rivers is now only found at very few sites in certain localized regions of south-western Ontario and Quebec. It is affected by various factors such as fluctuations in water level.

Canadian Occurrence: Ontario, Quebec

COSEWIC Status History: The species was designated "Threatened" in April 1984. Its status was re-examined and confirmed in May 2000, with the last assessment based on an updated status report.

1.2 Description

The American Water-willow (Justicia americana (L.) Vahl) is an aquatic herbaceous perennial that grows in colonies. It is the only representative of the Acanthaceae family in Canada. The plant has an erect stem that may be branched or unbranched, rising to a height of 20 cm to 1 m from a large rhizome that creeps along the ground. The leaves are undivided, narrow and elongated in shape, and occur in opposite pairs along the stem. White or pale violet, tube-shaped flowers appear on long thin stalks that originate at the junction of the upper leaves with the main stem. The fruit is a capsule which contains two to four beige or light brown seeds (Environment Canada, 2006).

1.3 Population and distribution

1.3.1 Global range and range in Canada

The American Water-willow's global range is part of eastern North America, extending from Texas and Georgia in the south to the southern regions of Quebec and Ontario in the north (Figure 1). Canada is home to less than 5% of all the populations of American Water-willow. It is present at very few sites (10) in Canada where distance between sites ranges from 2.5 km to 950 km.

In Quebec, the American Water-willow is found along the St. Lawrence River near Montreal and Lake Saint-Pierre, while in Ontario, it grows along the north shore of Lake Erie and in the Thousand Islands area (Figure 2).

This species has always been rare in Canada. According to historic records, there were once 11 occurrences in Quebec and 17 in Ontario. At present, there are three confirmed extant occurrences in Quebec and seven in Ontario. The other populations are considered historic or extirpated (Natural Heritage Information Centre (NHIC), 2010; Jolicoeur et Couillard, 2007) as their occurrence at the site has not been recorded in at least 20 years.

Figure 1. Global range of the American Water-willow

Gauvin (1983)

 

Figure 2. Distribution of extant and historic American Water-willow populations in Canada

Data sources: NHIC, 2010; White, 2000; Centre de données du patrimoine naturel du Québec (CDPNQ), 2006.

The American Water-willow has been designated as Threatened in April 1984 by the Committee on the Status of Endangered Wildlife in Canada and is listed since June 2003 on Schedule 1 of the Species at Risk Act (Environment Canada, 2006). It has been designated as Threatened according to Quebec law since 1998 (Ministère du développement durable, de l'Environnement et des Parcs, (MDDEP), 2005; Quebec, 2003) and is designated as Threatened in Ontario in the Species at Risk Act in Ontario List regulation under Ontario's Endangered Species Act, 2007 (Ontario Ministry of Natural Resources, 2009a). The American Water-willow's status^Footnote 1 is global rank secure (G5), national rank secure (N5) in United States, national rank imperiled (N2) in Canada and subnational rank critically imperiled (S1) in Quebec and Ontario.

1.3.2 Population size and trends

Based on the most recent data issued in October 2007, the total number of American Water-willow stems in Canada is estimated to be 25 500 000 (NHIC, 2010; Centre de données du patrimoine naturel du Québec, CDPNQ, 2006; Bisson et Gauvin, 2008; Michael Oldham, pers. comm., September 2006). The most important population is found at Mille Îles River (Que.), where an in-depth inventory conducted by Éco-Nature (Bisson et Gauvin, 2008) counted as many as 25 323 757 stems in 2007, making up 99% of all known stems counted in Canada.

In the U.S., colony density varies from 60 to 476 stems per m² (Howell, 1975), whereas at the northern limit of the species' range, this density ranges from 30 to 185 stems per m² in Quebec (CDPNQ, 2006) and 30-150 stems per m² (Thompson, 2008) in Ontario.

In Quebec, it is believed that urban expansion in the greater Montreal area and dredging for the St. Lawrence Seaway contributed to the species' disappearance from most sites (Jolicœur and Couillard, 2007). In Ontario, it is not known if the species was more abundant than it is now at these known occupied sites, except perhaps for Dufferin Island (near the Niagara River) and Point Pelee National Park, where historic data suggest that this was the case (Michael Oldham, pers. comm., December 2006, Varga, 1984).

In Point Pelee National Park, where several inventories were conducted over the years, numbers of stems have varied greatly and, overall, show a decline. The 2007 data (Jalava et al. 2008) suggests a large decline since 1983 (Varga, 1984; Kraus, 1991, Mouland, pers. comm. in White, 2000). One historic occurrence (last noted in 1990) at Redhead Pond was not found in 2007 despite targeted searches. In addition, the species was not found along the northern half of the Lake Pond shoreline where it had been formerly located. It is not possible to determine how much of this decline may be as a result of natural fluctuations. Given the dynamic nature of its habitat, population fluctuations are normal with this species and can occur such as in Ontario populations where it has been observed that the number of stems can naturally fluctuate from one year to the next (Michael Oldham, pers. comm. December 2006). It is thus possible that such naturally ephemeral colonies could become established and then disappear from time to time.

 

1.4 The needs of American Water-willow

1.4.1 Biological and habitat needs

This herb is normally found along the shores of rivers, streams and shallow lakes on a substrate of gravel, sand or organic material. The American Water-willow can survive in zones that are highly exposed to the action of waves (Varga, 1984) and is limited to open habitats offering little or no competition from other species. This trait explains the plant's tendency to form monocultures in which very few other floating, submerged or emergent species are found.

The American Water-willow survives equally well just above ground water level as it does in up to 1.2 m of water. Its roots always remain below the ground water, even when water levels fall to their lowest (Gauvin, 1983; Varga, 1984). It appears that the herb's survival in the dynamic environment of streams in eastern North America is aided by its solidly rooted underground structure and its ability to regenerate in the wake of storms. The dynamic environment in which the American Water-willow grows suggests that its life cycle is probably adapted to natural phenomena like erosion.

The plant cannot survive in a pH of 5.5 or lower (Koryak and Reilly, 1984; Adams et al., 1973). American studies have shown that hard water and an abundance of organic material encourage the growth of American Water-willow (Hill, 1981; Howell, 1975).

The American Water-willow can propagate through vegetative reproduction, with new plants developing from its rhizome or from axillary buds that form on the stem. Rhizome-based propagation occurs when there is an accumulation of soil, whereas axillary buds are produced most frequently in the absence of sedimentation.

Sexual reproduction can also play a significant role in the propagation of this aquatic plant (Penfound, 1940). Recently, the species has been successfully cultivated using two seedlings removed from their natural environment by the Institut de recherche en biologie végétale at the Montreal Botanical Garden and the Université de Montréal (Guy Jolicœur, pers. comm. with Stéphanie Pellerin, November 2006).

1.4.2 Limiting factors

In Canada, the American Water-willow grows at the northern limits of its range. Climate appears to be the primary factor that limits the distribution of the American Water-willow in Canada (Gauvin, 1983; Jolicœur and Couillard, 2007). Dispersal and pollution may also play a role (White 2000) but there is no direct evidence for the type of impact water pollution may have on Canadian populations. Flooding and drought can occur at most sites of American Water-willow, but their effects are not fully understood and do not appear to be uniform (see section 1.5.2.1). According to White (2000), the American Water-willow may be ephemeral at some sites.

1.5 Threat identification

Table 2 and the associated section present all the known or presumed threats to the survival of the American Water-willow and its habitat. At present, the species occurs at only ten known sites in Canada. Information pertaining to the Grenadier Island, Lyon's Creek, Pelee Island and Leamington sites is not included in this table due to lack of available information.

The definitions of the terms used in the threat table are as follows:

Causal certainty: reflects the degree of evidence that is known for the threat - the stronger the evidence, the higher the rating (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g. expert opinion; Low: the threat is assumed or plausible).

Severity: reflects the population-level effect (High: very large population-level effect, Moderate, Low, Unknown).

Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, considering the information in the table.

1.5.2 Description of threats

The threats to the survival of the American Water-willow are linked mainly to changes in its habitat, including changes in water regime, loss of habitat resulting from natural processes such as erosion and from human activity such as dredging and infilling. Competition from invasive plant species in the American Water-willow's habitat and human-induced trampling, have a high impact at certain sites and also constitute threats to the population's integrity.

 

 

 

 

 

 

 

 

Additional information: The Grenadier Island stand is partially cut to accommodate an intake line for cottage water supply. Hill Island had one site browsed by deer.

1.5.2.1 Changes to water regimes

The effects of flooding and drought on American Water-willow populations are not fully understood and available information about this threat vary greatly on the nature of its impact on the plant's survival. Such effects on populations are sometimes noted as positive and sometimes as negative.

The operation of the dam built on Dufferin Island (near the Niagara River) likely affects the survival of downstream American Water-willow populations by creating regular successive periods of drying out and inundation. This may have been the cause of an apparent decline in numbers at the Dufferin island site (Michael Oldham, pers. comm., December 2006).

The St. Lawrence River experiences annual fluctuations in water levels of 60 to 90 cm in the Thousand Islands area. Plants were observed in September with previously flooded roots left high and dry. This could be a compounded problem if roots are left exposed to more severe cold and freezing in winter under low water conditions (OMNR, 2009b).

In the Mille Îles River, in Quebec, annual monitoring of the populations between 2004 and 2007 revealed that very little about the direct effect of the modifications to the water levels is known since, with a low water level, both decreases (2005) and increases (2007) in American Water-willow populations (Bisson et Gauvin, 2008) were observed.

According to White (2000) the American Water-willow populations can be seriously affected by natural changes in water regimes. Likewise, water regime changes caused by human activity can also have major consequences for this plant. A recent study in the U.S. (Strakosh et al., 2005), demonstrated that the American Water-willow is impacted by the negative effects of flooding more than those of drought. In other studies, it appears that the growth of American Water-willow was in no way affected by disturbances caused by flooding (Fritz et al., 2004).

Overall, these studies show that the effects of flooding and drought on American Water-willow are not uniform.

1.5.2.2 Erosion

Habitat loss related to erosion can be a medium to low threat that can be attributed to natural causes in most cases, but arises from human activities in certain places. In Ontario, the shores of Lake Erie bear the brunt of storms, waves, wind and winter ice, which cause erosion contributing to American Water-willow habitat loss (White, 2000). Regular operation of the dam at Dufferin Island has modified the nature of the river bed at the site. Shoreline erosion and habitat succession may have eliminated the American Water-willow at two of the three Pelee Island sites (White, 2000) and may affect the newly discovered site. Wave action noted at the Hill Island colony may be uprooting portions of colonies. The waves may be caused by heavy boat traffic and/or wind (OMNR, 2009b).

It is anticipated that these natural threats could likely intensify as a result of climate warming. Anticipated changes in the water level of the Great Lakes will also likely pose a considerable threat to the species and will need to be examined in greater depth (Michael Oldham, personal communication, November 2007). In Quebec, certain sectors along the Mille Îles River have suffered extensive erosion following human activities such as wall building along the shoreline and other kinds of alterations to the natural banks (Isabelle Mathieu, pers.comm., fall 2006).

1.5.2.3 Alien invasive species

In Point Pelee National Park, the Common Reed (Phragmites australis) and the Hybrid Cattail (Typha X glauca) effectively reduce the amount of edge habitat where American Water-willow is most often found (Michael Oldham, personal communication, 2007). Reed Canary Grass (Phalaris arundinacea) and shoreline shrubs also tend to hem in the area that can be occupied by American Water-willow higher up on a bank. The American Water-willow can establish itself higher on the bank only when Reed Canary Grass is absent. In the areas where American Water-willow has disappeared in Point Pelee National Park, Common Reed now grows in a monoculture. It may very well be responsible for the local disappearance of American Water-willow at one pond in the national park (M^cKay pers. comm.).

In southern Ontario especially, invasive species like the Common Reed, Hybrid Cattail, Purple Loosestrife (Lythrum salicaria) and Yellow Flag (Iris pseudacorus) can constitute a serious threat (Michael Oldham, personal communication, December 2006). There is always a potential risk of other invasive species becoming established and increasing the cumulative impact of invasive species on the American Water-willow.

1.5.2.4 Trampling by hunters, canoeists and kayakers

Trampling by hunters, canoeists and kayakers mainly affects the Ile Rock population of American Water-willow. Hunters visit the island in the fall, while kayakers and canoeists are more likely to picnic there during spring, summer or fall and intensely use the area for the practice of this sport. Moderate impacts on the population are expected (P.Asch, pers. comm.) if recreational use of the area encompassing the island remains at same level. In the fall, the plants have already produced their rhizomes and seeds. According to Penfound (1940), these seeds may have even germinated by fall, which would render these seedlings vulnerable to trampling.

The American Water-willow population at Point Pelee National Park may also suffer the negative effects of trampling by canoeists and kayakers. However, it is also possible that the occasional disturbance caused by this trampling may in fact keep the habitat clear from the encroaching Common Reed. As such, concern for this particular threat at this location is considered low at this time.

1.5.2.5 Infilling

Habitat loss caused by infilling of river shores to expand urban areas constitutes a serious threat that has already been instrumental in the extirpation of seven of the twelve American Water-willow populations previously found in Quebec. Evidence on the subject comes mainly from sites where the species occurred in Quebec, along the St. Lawrence Seaway and in the greater Montreal area (Jolicœur and Couillard, 2007). This threat still exists in the Mille Îles River area as colonies exist in close proximity to well-developed urban areas. Little is known of the historical importance of this threat in Ontario. It is presumed that many populations have disappeared due to the destruction of their habitats as a result of human activity.

1.5.2.6 Grazing by wild animals

Along the Rivière Godefroy, intensive grazing on American Water-willow tips by White-tailed Deer (Odocoileus virginianus) has been observed. The browsing observed at Rivière Godefroy showed that stems were stimulated to sprout again. On the other hand, the plants observed showed very little fruit, probably indicating a decline in reproductive success.

At one Hill Island colony (one of 24 present), approximately 20-25 % of the stand was affected by deer browsing (Thompson, 2008). Grazing may have contributed to the loss of the American Water-willow population in Rondeau Provincial Park (Ont.), (an historic occurrence), since the number of White-tailed Deer was, at one time, very high there.

1.5.2.7 Degradation of water quality

According to U.S. studies (Hill, 1981; Howell, 1975), hard water and an abundance of organic matter encourage the development of the American Water-willow. On the other hand, the species is harmed by industrial pollution (Stuckey and Wentz, 1969) particularly acid effluents from mines (Adams et al., 1973; Koryak and Reilly, 1984). The American Water-willow cannot survive in water with a pH of 5.5 or lower. No specific information regarding this threat exists for Canadian sites.

1.6 Actions already completed or underway

In 1983, a detailed study of the status and management of the American Water-willow population and its habitat was conducted at Point Pelee National Park, and follow-up monitoring was conducted in 1988, 1989, 1991, 1999 and 2007. In 1990, the majority of the Ontario American Water-willow populations were inventoried and a summary report on their status was produced (Oldham, 1990).

In 1998, the American Water-willow was officially designated as Threatened in Quebec and the Rivière Godefroy and Ile Rock sites were recognized as "plant habitats" under the Act respecting threatened or vulnerable species of Quebec^Footnote 2. These sites thus gained a high degree of protection, because most human activities are prohibited in such habitats. A Quebec conservation plan for the conservation of the American Water-willow at actual sites of occurrence in Quebec was drawn up in 2004 by the ministère du Développement Durable, de l'Environnement et des Parcs du Québec and has recently been updated (Jolicœur and Couillard, 2007).

In 2002 and 2003, an unsuccessful attempt was made at relocating American Water-willow on Île Turcotte (Saint-Eustache) on the Mille Îles River. From 2004 to 2008, American Water-willow populations on the Mille Îles River were monitored by the group Éco-Nature (Bisson et al., 2004, 2005, 2006, and Bisson et Gauvin, 2008). This group is heightening awareness of American Water-willow on the part of fishers and other Mille Îles River users through various means. Direct contact was also made with landowners at some sites to suggest proper management practices regarding shoreline use with regard to the American Water-willow occurring there. In 2005, the Rivière Godefroy habitat for this protected species was expanded and a notice and a chart were published in the Gazette officielle du Quebec^Footnote 3.

In 2006, in Ontario, the Niagara Parks Commission conducted a survey of Dufferin Island and undertook two initiatives to improve American Water-willow habitat and to establish an educational program for 2007. In 2007, surveys of known American Water-willow sites were conducted at Ile Rock, Dufferin Island, Lyon's Creek, Rondeau Provincial Park, Middle Island, Point Pelee National Park and several sites on Pelee Island.

In 2008, two new sites were discovered in Ontario's Thousand Islands region, (near Grenadier and Hill islands) in the vicinity of St.Lawrence Islands National Park and a thorough survey of several neighboring islands was conducted in 2008 after the initial plants were discovered. In 2009, surveys were carried out at Long Point National Wildlife Area on Lake Erie and no plants were observed in apparently suitable habitat where it historically occurred.

Current initiatives for the conservation of this species include a project to designate the Mille Îles River site as the habitat of a protected species. This work is being developed by the Quebec ministère du Développement durable, de l'Environnement et des Parcs (MDDEP).

1.7 Additional American water-willow information requirements

1. To date, there is no exact information that enables an evaluation of the long-term viability of a population. A mechanism to determine what is considered to be a self-sustaining viable population size would inform future recovery initiatives.

2. There is a need to document threats and to verify the significance of these threats, at each site, based on credible evidence.

3. Surveys still need to be conducted on sites where American Water-willow has occurred historically and at sites where there is potentially suitable habitat.

4. The extent of variation in population dynamics needs to be studied, so as to determine the rate of natural population fluctuations.

5. Methods of propagating, transplanting and establishing individual plants are to be refined if augmentation of existing colonies is to be realized. Such an activity would need to be based on a study evaluating pertinence and technical feasibility of transplanting individuals at appropriate sites.

6. Most of the references consulted for information on the species' ecological needs and ecological role come from American sources. There seem to be no studies of this type on Canadian populations. The physico-chemical parameters of water in Canadian colonies of the American Water-willow remain unknown. A detailed characterization of the micro-habitats occupied by this species in this country is required.

7. First Nation communities have maintained local ecosystems for generations through the use of community Traditional Ecological Knowledge. It is important to gather and share Traditional Ecological Knowledge from Knowledge Holders to others as a means for species and ecosystem protection and recovery. Traditional Ecological Knowledge and Science can, together, better inform assessment, monitoring, and recovery of the ecosystems that support specific species at risk.

8. Since the species produces numerous rhizomes that interconnect and thereby anchor plants firmly in the substrate, it is possible that each site actually consists of only a few clonal individuals. Knowledge of the relative importance of the rate of reproduction by seeds (sexual) as opposed to rhizomes (vegetative) would be useful in the long term. In order to assess the long term viability of any colony, its genetic structure should be analyzed in order to assess the level of cloning (asexual reproduction) occurring within it.

9. Little is known about the role of sexual reproduction in the propagation of the species and about the viability of the seeds produced by plants. Similarly, modes of pollination and seed dispersion at our latitudes are poorly documented. The largest Quebec populations studied in 2006 were observed to have an abundant production of fruit, but the role of fruit in the species' maintenance and expansion is not known (Jolicœur and Couillard, 2007). Information on fertility is also lacking for the Ontario populations.