Victorin's water-hemlock (Cicuta maculata) COSEWIC assessment and status report: chapter 8
Predation
The umbels and fruits of the plants at the localities visited in 1997 and 2002 were covered with hundreds of aphids. This phenomenon had not been observed at the sampling sites in 1995 or 1996.
Spotted water-hemlock is a host to the fungal pathogens Puccinia cicutae and Uromyces lineolatus (Ginns, 1986). Victorin’s water hemlock may also be a host to these pathogens.
Mowing
Mowing of the littoral zone by property owners has been observed at some localities. Mowing prevents the formation of flower stalks and therefore deprives the plants of their only means of reproduction. This could result in its extirpation from certain localities where this has occurred.
Limited habitat
Victorin’s water-hemlock is confined to the freshwater and slightly brackish intertidal zone. Its habitat in Quebec is restricted by the small amplitude tides upstream from Sainte-Anne-de-la-Pérade and the higher water salinity in the Saint-Jean-Port-Joli region downstream.
Ice scouring
Some plants may be torn up by ice scouring of the rocks and river banks during the daily tides and by the spring ice break-up.
Water quality and level
Although the water quality of the St. Lawrence River is improving, it is still polluted. Riverbank erosion caused by waves generated by ships and recreational watercraft could adversely affect the species. As in the case of Provancher’s fleabane and Victorin’s gentian (Sabourin and Paquette, 1991; Coursol, 1998), riparian colonies of Victorin’s water-hemlock along the St. Lawrence could be adversely affected by an oil spill.
Filling
Filling of the riverbank for the construction of homes, roads, railways and marinas has resulted in the loss of habitat of several species along the River. For example, the construction of Champlain Boulevard and the Dufferin Highway at Quebec City has destroyed virtually the entire natural river bank between Sainte-Foy and Boischâtel, thereby preventing potential recolonization by Victorin’s water-hemlock. The same is true with respect to the filling of the upper littoral and the construction of retaining walls for many homes in Lévis, Saint-Romuald and several other residential sectors along the River.
Human trampling
Victorin’s water-hemlock populations are highly exposed to human trampling and/or ATV traffic. ATV traffic in the intertidal zone poses a significant threat. ATVs not only cause plant mortality, but also significantly alter the fragile balance of its habitat. Thus, the Victorin’s water-hemlock population at Lotbinière is probably extirpated due to the repeated passage of ATVs in the upper littoral zone, where they disturb a swath from two to sometimes 10 metres wide. The report by Legault (1986) reported this problem for this locality. ATV activity has also been noted at the Saint Augustin-de-Desmaures site. In general, ATV activity is scattered along the St. Lawrence R. but the impact is particularly noticeable at the Lotbinière site.
Agricultural Abuses Act
Under the Agricultural Abuses Act (R.S.Q. A-2), water hemlock (Cicuta maculata) is considered a weed when it grows along roads and highways, railways, electric power transmission lines and in ditches on agricultural land, other land and vacant lots. Owners are required to destroy weeds by government order, before the seeds mature. Given that varieties of water hemlock are identified primarily on the basis of their seeds, it is possible that Victorin’s water-hemlock may be torn up unintentionally. The lack of provisions in the Act regarding the variety of water-hemlock creates confusion among the public and among inspectors of the Quebec Department of Agriculture, Fisheries and Food. No specific losses have been documented resulting from the enforcement of this Act but the lack of clarity in the Act could potentially result in populations being impacted.
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