The scene is breathtakingly beautiful, a thick brush of purple flowers blanketsCanada’s wetlands. This blanket silences the expected sounds of the wetlandenvironment, birds chirping, ducks splashing, insects buzzing and animalsthriving. This unnatural silence is disturbing, the favourite flowers that usedto litter this landscape are no longer visible, the water that used to ripplecontinuously is perfectly still.
The wetland is dead, except for thisoverpowering, hardy purple flower that has choked out all other vegetation andspecies. Purple loosestrife now controls this landscape. Purple loosestrife is an exotic species that was introduced to North Americafrom Europe during the early 1800’s. Europeans sailing to North America wouldfill their ships ballast with wet sand taken from shores of Europe, a habitatwhere purple loosestrife thrived.
Upon arrival in North America the ballastwould be dumped overboard on the shoreline. By 1830 the plant was wellestablished along the New England seaboard. Purple loosestrife seeds were alsofound in sheep and livestock feed that was imported from Europe during thisperiod. This new organism was introduced to a new habitat free from traditionalparasites, predators and competitors, purple loosestrife thrived in theenvironmental conditions and by 1880 was rapidly spreading north and westthrough the canal and marine routes. Purple loosestrife stands also increaseddue to the importation of seeds and root stalks by horticulturists.
It wasintroduced to many communities as an herb, an ornamental garden flower and as adesirable honey plant. One of the earliest reported studies of purple loosestrife being a problem inCanada was documented by Mr. Louis – Marie, in 1944. He stated that purpleloosestrife was invading the St.
Lawrence flood plain pastures between Montrealand Quebec. At that time Louis – Marie conducted a study to find suitablecontrol methods for purple loosestrife. His results indicated that repeatedmowing, continuous grazing, deep discing and harrowing were effective in keepingthe spread of purple loosestrife controlled on agriculture land. Since the1940’s purple loosestrife infestations have increased greatly and the plant isnow a major problem threatening many wetland ecosystems across North America. Figure 1 – Purple loosestrife flowers. (Parker 1993)Lythrum Salicaria, commonly known as purple loosestrife belongs to theLythraceae family, which consists of 25 genera and 550 species worldwide.
Thegenus Lythrum consists of thirty – five species, two of which are located inNorth America, Lythrum Purish which is native to the continent and the invasivepurple loosestrife. Through cross breeding, purple loosestrife is quicklyovertaking Lythrum Purish and causing a decrease in native species. “Thegeneric name comes from the Greek luthrum, blood, possibly in reference to thecolour of the flowers or to one of it’s herbal uses, as an astringent to stopthe flow of blood. ” (Canadian Wildlife Federation 1993, 38) Purple loosestrife,an aggressive, competitive, invasive weed often grows to the height of a humanand when it is mature can be 1. 5 metres in width. The stalk of the plant issquare and woody and may grow to 50 centimeters in diameter.
The perennialrootstock can give rise to 50 stems annually which produce smooth edged leaveson oppositesides of the stalk. Purple loosestrife flowers are long pink andpurple spikes which bloom from June to September (Figure 1). One purpleloosestrife plant alone is solid and hardy but when this plant invades an areait creates a “dense, impermeable stands whichFigure 2 – Purple loosestrife growing in a typical habitat. (Parker 1993)are unsuitable as cover, food or resting sites for a wide range of nativewetland animals.
. . ” (Michigan Department of Natural Resources 1994). Due to thelack of predators which feed upon purple loosestrife, this dominant plant has anadvantage when competing against most other native wetland species for foodsunlight and space. These advantages allow purple loosestrife to create dense,monotypic stands which reduce the size and diversity of native plant populations.
Purple loosestrife can also grow on a range of substrates and under nutrientdeficit conditions. It has the ability to regenerate quickly after cutting ordamage and can withstand flooding once adult plants have been established. Thereare no native species that are as hardy as purple loosestrife, therefore withoutcompetition and predators the wetland ecosystem cannot control the spread ofpurple loosestrife. Purple loosestrife is now found world wide in wet, marshy places, coastal areas,ditches and stream banks. (See Figure 2) It is prevalent in most of Europe andAsia, the former USSR, the Middle East, North Africa, Tasmania, Australia andNorth America. It has not been found in cold
