|Photo ©USDA Forest Service, Ottawa National Forest|
Hybrids: Natural C. palustre × C. arvense hybrids occur in England and other European countries (Sledge 1975 cited in ). These hybrids are possible where these species grow together in North America .SYNONYMS:
Marsh thistle was reported in New England by 1902 and in the Great Lakes area by 1934 (review by ). In New Hampshire, marsh thistle was first reported from East Andover in 1902. Plants occurred over a nearly 20-acre (8 ha) area in a "moist forest tangle" that was more than a mile (1.6 km) from the nearest town or cultivated area. Method of introduction was unknown. Marsh thistle was reported in South Boston in 1908 and in Newfoundland in 1910 . In 1944, marsh thistle was reported in several communities near Halifax, Nova Scotia . In Michigan, marsh thistle was first collected from Marquette County in 1934 . It was first recorded in Wisconsin in 1961 . In British Columbia, marsh thistle was first reported in 1954 . Marsh thistle was reported during a 1964 survey of a ponderosa pine (Pinus ponderosa) forest in northwestern Nebraska . However, no other sources reported marsh thistle in Nebraska as of 2009, suggesting that this population was transient or incorrectly identified.
Local distribution changes: The range of marsh thistle in North America is "rapidly expanding". Marsh thistle populations in Europe occur almost as far north as the Arctic Circle, suggesting marsh thistle could grow and spread throughout the boreal forest regions of North America . In Wisconsin and Michigan, the area occupied by and the abundance of marsh thistle have increased since its introduction and continue to increase . Marsh thistle was first recorded in Michigan in 1934 and by 1956 was considered locally frequent and common in Michigan's Upper Peninsula and on islands in the Straits of Mackinac [78,79]. By 1959, marsh thistle spread to the Lower Peninsula, and it continues to spread south. "Dense, ungainly colonies" occupy miles of ditch banks in Michigan, and populations have spread into adjacent natural areas . Although marsh thistle has occurred in British Columbia since the 1950s, its spread has been more recent. A "diminutive patch" of marsh thistle west of McBride, British Columbia, was reported in 1991, but marsh thistle had spread at least 130 miles (210 km) by early 2000. Spread occurred primarily along roadways and through river valleys . For more on the potential impacts of marsh thistle persistence and spread, see Impacts and Control.HABITAT TYPES AND PLANT COMMUNITIES:
In southeastern Scotland, marsh thistle is common in colonial bentgrass (Agrostis tenuis) grasslands on poorly drained sites . On coastal dunes in the Netherlands, marsh thistle is common in oneseed hawthorn-European white birch (Crataegus monogyna-Betula pendula) woodlands with ground water at or near the soil surface . Marsh thistle is also described in surface water-fed sedge fens , bare sandy sites, and open sites with chee reedgrass (Calamagrostis epigejos) and seaberry (Hippophae rhamnoides) .North American habitats and plant communities: In North America, marsh thistle occurs in wetlands, moist meadows, and forest openings [17,41]. In Wisconsin, it occurs in sphagnum (Sphagnum spp.) bogs, wet roadside communities, sedge marshes, and black spruce (Picea mariana) swamp openings . In Michigan, marsh thistle populations along ditch banks have spread into adjacent northern whitecedar (Thuja occidentalis) swamps and shaded fens . In New England, marsh thistle is reported from coastal beach and dune communities, coastal grasslands, early-seral forests, forest edges, floodplain forests, herbaceous wetlands, and other disturbed areas . Additional information on common marsh thistle habitats is reported in Site Characteristics.
At maturity, marsh thistle is generally an erect forb with a single branching stem. Plants may reach 6 feet (2 m) when flowering . Stems are spiny and winged because a portion of the leaf blade is attached to the stem. Most plant parts are covered with long sticky hairs [37,54].
|Photo © J.C. Schou; Biopix.dk|
Marsh thistle is best described as a monocarpic perennial. Plants often reproduce within 2 years but may take longer [19,36,56]. Rosette leaves are long, spiny, and deeply lobed [17,83]. In Jutland, Denmark, many marsh thistle plants remained vegetative for 2 or more years. All plants died after flowering, unless they were damaged during the flowering stage, in which case they regrew the next year . Another researcher reported that marsh thistle generally flowered at 4 years old in its native range (Linkola 1935 cited in ). In 2 seashore meadows in Tullgarn, Sweden, most (68-86%) marsh thistles flowered 3 years after germination, while the rest flowered later. In this area, the researcher noted a small number of marsh thistle plants flowering twice . Damage to these plants was not reported, but grazing and trampling were common in the area. (See Vegetative regeneration for another report of marsh thistle flowering in successive years.)
|On flowering stems, alternate leaves are 6 to 12 inches (15-30 cm) long near the base but shorter
near the top. Leaf spacing is generally much wider near the top than at the base of the plant
[17,83]. Spines up to 6 mm long
occur along leaf margin lobes .
Marsh thistle flower heads also appear spiny . Perfect disk florets occur in heads that develop on short branches at the end of the stem [19,36, 36,79]. Few to many flower heads may be produced . Heads typically measure 0.4 to 0.6 inch (1-1.5 cm) across .
Marsh thistle produces achenes that measure between 2.5 and 3.5 mm and are attached to a feathery pappus of fine cottony hairs [17,19,37, 83]. The pappus is typically less than 0.4 inch (1 cm) long , and achenes average 2 mg (Grime and others 1988 cited in ).
Marsh thistle produces a taproot with clusters of fibrous roots [17, 36]. It lacks rhizomes . In Jutland, Denmark, root development of vegetative marsh thistles was described in detail. Increased root growth coincided with increased leaf growth and increased flowering probability. Twenty-three percent of plants in the 3rd vegetative life stage (described in the table below) flowered the next year, while 79% or more plants in 4th vegetative life stage flowered the next year. All plants died after flowering .
|Photos ©Steve Garske, Great Lakes Indian Fish & Wildlife Commission|
|Below- and aboveground growth of marsh thistle in Denmark |
|Stage of vegetative development||2nd vegetative life stage||3rd vegetative life stage||4th vegetative life stage|
|Number of rosette leaves||3-4||3-5||8-18|
|Leaf width (mm)||19-45||35-73||85-123|
|Leaf length (mm)||150-360||180-400||300-600|
|Diameter of taproot (mm)||3.1-5.0||5.5-8.0||11.0-22.0|
|Length of taproot (mm)||30-50||20-50||30-40|
|Number of lateral roots||9-18||15-30||30|
Similar native species: In the Great Lakes, New England, and eastern Canada, marsh thistle occupies habitat similar to that of the native swamp thistle (Cirsium muticum). Swamp thistle lacks stem spines and produces less spiny-looking flower heads than marsh thistle .Raunkiaer  life form:
Seeds from self-pollinated plants may have lower viability than seeds from cross-pollinated plants. Self-pollinated marsh thistle plants from mountain habitats in Monmouthshire and sea cliff habitats in Gower, England, produced significantly less viable seed than cross-pollinated plants . Field experiments in 3 marsh thistle populations north of The Hague in the Netherlands revealed no significant differences in the germination of seed from cross-pollinated plants and plants protected from insects. Marsh thistle populations occurred in a dense birch (Betula spp.) woodland, a grassland, and a bare sandy site. Seeds produced by cross-pollinated plants weighed significantly (P<0.01) less than those produced by protected plants. Although some dispersal had occurred by the time production was evaluated, seed production of cross-pollinated plants exceeded that of protected plants by as much as 58.9%. Production differences were not significant . Germination, seedling establishment, and plant survival based on pollination method are discussed more in the sections below.
Seed production: Reviews report that a single marsh thistle plant may produce up to 2,000 seeds [41,56]. A vernalization period is considered necessary for flowering . Flowering date, flowering stem height, site conditions, and predation may affect marsh thistle seed production. In seashore meadow habitats in Tullgarn, Sweden, late-flowering marsh thistle plants produced more flower heads and generally had greater reproductive output than early-flowering plants. Reproductive output also increased with increasing height of the flowering stem (R² =0.646, P<0.0001) . In a dune area north of The Hague, marsh thistle populations averaged 24.1 seed-producing flower heads/plant and produced between 300 and 2,000 seeds/plant. There were many undeveloped seeds in the flower heads; the largest percentage of undeveloped seeds occurred in populations that were inundated for parts of the summer. Shade did not impact seed development [75,76], although other research suggests that shading can limit seed production (see Shade tolerance).
Field observations made near The Hague showed that moth (Epiblema scutulana) larvae and rabbits that fed on marsh thistle stems reduced flower head production by an average of 25.2% and 31.8%, respectively . When seeds were sown in dune areas near The Hague, counts 2 weeks later suggested seed predation levels of 60% to 80% .
Seed dispersal: Wind is likely the most common dispersal mechanism for marsh thistle seeds, but seeds may also be dispersed by gravity, in water runoff, or by animals and equipment [41,42]. Marsh thistle seeds are attached to a "thistle-down" pappus that aids in wind dispersal . A review reports that while most marsh thistle seeds fall within 33 feet (10 m) of the parent plant, high winds may carry seeds several kilometers . Wind dispersal distances may be reduced by increased densities and heights of neighboring plants , decreased heights of marsh thistle plants , and increased seed weights .
From laboratory experiments and achene and pappus measurements, researchers calculated that marsh thistle seeds could be dispersed a maximum of 22 feet (6.8 m) in 10 mile (16.4 km)/hour winds. Seeds released from a 36-inch (90 cm) height traveled a maximum of 7.5 feet (2.3 m) and 15 feet (4.5 m) in wind speeds of 3.4 miles (5.5 km)/hour and 6.8 miles (10.9 km)/hour, respectively. Researchers noted that dispersal distances would likely be less in dense stands, where wind speeds are reduced and obstructions are increased . Based on these calculations, researchers suggested seed dispersal distances could be reduced 35% to 50% when marsh thistle plant heights were reduced 16% by larval insects feeding on plant stems . Dispersal distance changes as a result of the greater seed weights of self-pollinated plants were not calculated, but researchers suggested that heavier seeds fell closer to the parent plants .
During seed trapping studies conducted in peat-harvested areas in Finland, marsh thistle seeds may have dispersed distances of 160 feet (50 m) or more. In one area, 1 marsh thistle seed/m² was recovered from seed traps located 820 feet (250 m) from the forest edge. There were no mature marsh thistle plants reported in the trapping area. Seed traps 160 feet (50 m) from the forest edge collected 16 marsh thistle seeds/m² . This study, however, was not designed to directly estimate seed dispersal distances. In another seed-trapping study in an eastern Scotland grassland, marsh thistle was collected from traps but not from soil in plots where vegetation was herbicide-killed. Traps contained less than 10 marsh thistle seeds/m², and the distance to the nearest mature plants was not reported. Researchers indicated that seeds were likely transported by wind, but may have been transported in surface water runoff or in animal fur or feathers .
It is likely that marsh thistle seeds are transported by equipment, but direct evidence is lacking. A review suggests that logging equipment may have transported marsh thistle seed. In British Columbia, new marsh thistle populations have been reported on mechanically-disturbed sites hundreds of kilometers from existing populations . In hay fields in the northern Netherlands, marsh thistle was present but its seed was not collected from haying equipment used for mowing in August . Although seeds were not recovered from mowing machinery, haying equipment may still have contributed to marsh thistle seed dispersal. It is possible that seeds had fallen off before counts were made or that seed was dispersed in the mowed area by blowing motors.
Seed banking: Although many have studied marsh thistle seed bank dynamics and attempted to determine the longevity and persistence of seed in the soil, findings and conclusions from these studies disagree. Some suggest a short-lived seed bank , while others suggest a persistent seed bank [46,63]. Methodology and scope of marsh thistle seed bank studies differ, making them difficult to compare and evaluate. It is possible that a portion of marsh thistle seed germinates immediately following dispersal , but a smaller portion fails to germinate, becomes dormant, and develops germination requirements different from those of fresh seed . Of seeds collected from plants near The Hague, 40% germinated after 1 year of burial .
Experiments conducted in Wellesbourne, England, suggested that seeds did not persist more than 3 years in the soil. Marsh thistle seeds were mixed with soil and put in a container that was sunk into the ground in September. Soil was mixed 3 times/year and emergence monitored. Most seeds germinated within a year and most germinated in the spring, although some fall germination occurred. Not all sown seeds were recovered, and the researcher suspected that seeds covered by 3 inches (7.5 cm) of soil germinated but failed to emerge .
|Emergence of marsh thistle seeds over time in England |
|Time in the ground||4 months||1 year||2 years||3 years||4 years||5 years|
|Percentage of seeds emerging||8.8%||33.3%||0.2%||0.1%||0||0|
Increasing depth of burial increased the survival of buried marsh thistle seed in the Netherlands. In a field experiment, 4% of marsh thistle seeds survived 27 months of burial at 2- to 5-inch (5-10 cm) depths, and 40% of seeds survived the same amount of time at 6- to 8-inch (15-20 cm) depths .
Soil samples collected from 95- to 150-year-old European beech (Fagus sylvatica) woodlands in southern Sweden rarely contained marsh thistle seed. Soil samples were collected in April at least 330 feet (100 m) inside the woodland edge. Surveys revealed no marsh thistle seedlings in the woodland. Fourteen marsh thistle seedlings/m² emerged from the top 2 inches (5 cm) of mineral soil collected from 1 of the 7 sampled sites. Researchers noted that after clearcutting, marsh thistle was common in the area. Because marsh thistle did not emerge from all soil samples, researchers supposed that emergence on cleared sites resulted from recent long-distance seed dispersal and not a persistent seed bank .
Based on several field and greenhouse observations and experiments, Pons  concluded that marsh thistle seed does persist in the soil seed bank. In the Netherlands, marsh thistle is common following cutting in ash (Fraxinus spp.) stands. Marsh thistle seedling emergence was compared in soil samples taken from sites cut 7 years earlier. Soil was collected from an undisturbed site and a site where soil had been artificially disturbed. Just 19 marsh thistle seedlings/m² emerged from undisturbed soils, and 497 marsh thistle seedlings/m² emerged from disturbed soils, suggesting that emergence was not limited to wind-dispersed seed on the soil surface but also came from soil-stored seed that was encouraged to germinate by the soil disturbance. In multiple follow-up experiments, Pons concluded that dormancy in marsh thistle seeds was triggered by high temperatures and reduced light levels. Exposure to light was the principal stimulus for germination of soil-stored seed, and brief light exposure during winter harvesting could allow for emergence several months later .
In a meadow in Poland's Bialowieza Primeval Forest, the density of marsh thistle in the soil and in aboveground vegetation generally decreased as succession progressed. The meadow was managed with regular mowing that was discontinued when the study began. Marsh thistle plants and seeds occurred in all stages of succession, 0 to 20 years since the last mowing, but density generally decreased as time since last mowing increased . Marsh thistle survival, growth, and development were also studied as succession progressed in this meadow (see Plant development and survival).
|Density of marsh thistle seed in the soil from a meadow as time since last mowing increased |
|Time since last mowing (years)||0||5||10||15||20|
|Dominant vegetation||Grasses||Grasses, increased proportion of tall forbs||Forbs||Sedges, some willow clumps||Willow clumps, still some tall herbs and sedges|
|Marsh thistle seed bank density (seed/m²)*||320||393||217||144||50|
|*Determined by separating seeds from soil; 40 samples (10×10×3 cm) were collected at each 5-year interval.|
Germination: Marsh thistle seeds generally germinate best in warm temperatures and full light after cold stratification. However, some germination occurs without stratification, in cool temperatures, and in the dark. Pollination method and parent plant litter can also affect germination.
During field studies in Tullgarn, Sweden, germination percentages for marsh thistle were very low; 0.2% to 0.4% germination in one meadow population and 9% to 17% germination in another meadow population .
Temperature, light, and moisture effects: Cold stratification and high light and moisture levels may produce the highest germination percentages for marsh thistle seeds, but seeds may also germinate without cold stratification and in the dark. Warm temperatures (≥54 °F (12° C)) are typically best for germination regardless of prior chilling and light conditions [24,45,75].
Increasingly cold temperatures significantly (P<0.001) increased the germination of marsh thistle seeds collected from a wet meadow in the Czech Republic. Germination was highest but was still less than 40% after 30 days at 6.8 °F (-14° C). At 68 °F (20° C), germination was less than 20% . Marsh thistle seeds collected from plants in the Netherlands, however, "gave no problems in germination", although other species required winter temperatures before germinating . Marsh thistle seeds collected in August from a sphagnum bog in England's Sheffield area also germinated well (91%) without cold stratification. After 3, 6, and 12 months of storage at 41 °F (5° C), germination was 50%, 88%, and 79%, respectively. In full light, germination was 90%; in the shade (2.4% of full light), germination was 86%. In the dark, germination was 36% . In other laboratory studies, germination of freshly collected marsh thistle seed ranged from 32% to 72% in the light and 0.8% to 20.7% in the dark. Storage at 39 °F (4 °C) reduced germination in the light and dark .
Laboratory findings suggested that marsh thistle seeds could germinate beneath ash canopies, but seedlings were rare in the understory. At low red/far red (R/FR) light levels that were slightly lower than those penetrating ash thickets in the Netherlands, freshly harvested or dry-stored marsh thistle seed germination was lower than at high R/FR light levels. Cold stratification increased germination at low R/FR light levels and at low temperatures. Germination failed even with stratification at a R/FR level of less than 0.2 .
Marsh thistle seeds failed to germinate at water stress levels of 0.25 MPa in the laboratory. Germination ranged from 69% to 57% up to water stress levels of 0.1 MPa but was reduced to 3.8% at 0.2 MPa .
Timing and parent plant effects: Researchers found that in a spring area in central Jutland, Denmark, marsh thistle seedlings from fall-germinating seeds were generally larger than those from spring-germinating seeds . Seedlings were rare beneath flowering marsh thistles or in the immediate vicinity of marsh thistle rosettes. In the laboratory, germination of marsh thistle seeds was significantly (P<0.05) lower when treated with extracts of marsh thistle leaf material than when untreated . Seedling growth may also be reduced in soil with marsh thistle leaf litter (see Seedling establishment, growth, and survival).
Pollination method effects: In the Netherlands, marsh thistle seeds from plants protected from insects germinated at a greater percentage and rate than seeds from cross-pollinated plants. After 4 days, germination of seeds from cross-pollinated plants (1.6%) was significantly (P<0.01) less than that of seeds from protected plants (19.7%). After 14 days, germination differences were still significant (P<0.05); 77.4% of seeds from cross-pollinated plants and 87.7% of seeds from protected plants germinated . Seedling emergence and survival may also be reduced in cross-pollinated plants (see Seedling establishment, growth, and survival).
Seedling establishment and growth: Open sites are likely best for marsh thistle seedling emergence and establishment. Seedling growth and survival may be impacted by timing of germination, pollination of the parent plant, and presence of marsh thistle plant material in the soil. Growth, development, and reproductive success of plants 1 year or older are discussed in Plant development and survival.
Bare sites may favor seedling establishment. In a low-nutrient, species-rich meadow in the Czech Republic, almost no marsh thistle seedlings emerged from treatment plots where mosses, litter, and/or existing vegetation were left intact. Marsh thistle seedling emergence was greatest in plots where mosses and litter were removed . In England, gaps created by domestic sheep grazing were considered important to marsh thistle seedling establishment .
In a spring area in central Jutland, Denmark, seedling mortality was high (85%) regardless of emergence timing, but seedlings that survived their first winter had a high probability of surviving to reproductive age . Growth, reproduction, and survival of these seedlings were monitored in later life stages (see Botanical description), but spring- and fall-emerging cohorts were not studied separately .
|Characteristics of fall- and spring-emerging seedlings in Jutland, Denmark |
|Measured (mm) or counted attribute||Spring emergence||Fall emergence|
|Number of rosette leaves||2-3||2-3|
|Diameter of taproot||0.8-1.2||1.5-2.5|
|Length of taproot||20-30||20-30|
|Number of lateral roots||4||7-8|
In the Netherlands, seedlings from seeds produced by cross-pollination had significantly (P<0.05) lower overall emergence, fall emergence, and survival to 1 year old than seedlings produced by plants protected from insects. There were 100 seeds from protected plants and 100 seeds from cross-pollinated plants sown and monitored in the field .
|Fate of cross-pollinated and noncrossed seed sown in the Netherlands |
|Seed type||Cross-pollinated seed||Noncrossed seed|
|Total number of seedlings observed||44.3||57.0|
|Number of fall-emerging seedlings||8.7||17.2|
|Number of 1-year-old plants||10.5||15.8|
|All differences between cross-pollinated and noncrossed seeds were significant (P<0.05).|
Marsh thistle seedling growth may be reduced in the presence of marsh thistle leaf litter. Field observations in central Jutland, Denmark, revealed a rarity of seedlings beneath marsh thistle flowering plants or near marsh thistle rosettes. In a controlled study, marsh thistle seedling growth was monitored after 5 weeks in soils mixed with marsh thistle foliage. At a 0.25% foliage concentration, marsh thistle seedling growth was reduced by 52%, and at a concentration of 1.25%, was reduced by 65% .
Plant development and survival: Marsh thistle rosette diameter and probability of flowering are positively correlated. Rosette diameter and probability of flowering generally decrease as densities or canopy cover of associated vegetation increase.
In a greenhouse study, marsh thistle flowering was positively correlated with rosette size (r =0.40, P<0.05), and rosette size was negatively correlated with marsh thistle plant density (r =-0.38, P<0.05). The percentage of flowering plants was greatest when plant density was lowest and rosette diameter was greatest. Marsh thistle plants at the lowest density produced significantly (P<0.05) more fruits than those at moderate and high densities .
|Growth and reproductive fate of marsh thistle plants grown in different densities in the greenhouse |
|Density (plants/0.25 m²)||1||2||4|
|Average rosette diameter (cm)||34.8*||25.6*||20.6|
|Percentage of individuals flowering in 2nd year||90||60||25|
|Height of flowering shoot (cm)||139.7*||116.9*||102.2|
|*Values within the row are significantly different (P<0.05).|
In field studies in the Reski Range of Poland's Bialowieza Primeval Forest, marsh thistle population dynamics were studied within a single cohort and for many cohorts within different vegetation types. In a grassland area, a spring-emerging marsh thistle cohort was studied for 5 years. No plants flowered in their 1st year, and only 30% flowered in their 2nd year. The highest percentage of plants flowered in their 4th year .
|Fate of a marsh thistle seedling cohort monitored over 5 years in a grassland in Poland |
|Plant age (years)||Survival (%)||Flowering (%)||Rosette diameter (cm)
|Rosette diameter (cm)
As succession proceeded to grass-, forb-, patchy sedge-, and willow-dominated vegetation (5, 10, and 15 years after mowing) in the Bialowieza Primeval Forest, Falinska  conducted many studies and made several observations on marsh thistle populations, concluding that:
Vegetative regeneration: Marsh thistle does not reproduce vegetatively, but it may regenerate vegetatively following damage. Marsh thistle plants generally sprout following cutting . In Jutland, Denmark, if the inflorescence of flowering plants was damaged before ripe seed was produced, marsh thistle sprouted from rosette buds later in the season or in the next year .SITE CHARACTERISTICS:
Climate: In North America, marsh thistle is most common in moist areas with long cold winters . During a survey of major roadways in South Island, New Zealand, marsh thistle was generally restricted to cool, wet areas in a zone where the annual water deficit was less than 2 inches (50 mm) .
Climates are described from several European marsh thistle habitats, which may allow for a better prediction of its spread potential in North America. In Europe, marsh thistle populations occur almost as far north as the Arctic Circle, suggesting populations in North America could potentially spread through the boreal forest zone . In southeastern Scotland, marsh thistle is common in grasslands where the average February and July temperatures are 34.2° F (1.2° C) and 57° F (13.9 °C), respectively, and annual precipitation averages 35.2 inches (894 mm) . In south Wales, the climate is mild and oceanic. Temperatures average 39° F (4° C) in February and 59° F (15° C) in July . In the central and northeastern Netherlands, marsh thistle is common in sedge fens where annual precipitation averages 30.1 to 31.7 inches (765-806 mm) . In wet meadow marsh thistle habitats in Ceske Budejovice, Czech Republic, annual precipitation averages 24.4 inches (620 mm), and minimum and maximum temperature averages for July are 52.9° F (11.6° C) and 75.4° F (24.1° C) and for January are 20.8° F (-6.2° C) and 33.1° F (0.6° C) .
Elevation: Marsh thistle occurs at elevations from 30 to 2,600 feet (10-800 m) in North America .
Soils: In marsh thistle habitats in North America, soils were rarely described in detail. In Canada, marsh thistle grew in organic wetland soils and in coarse gravelly soils along roadsides. Large populations and high densities were often associated with high water tables . Marsh thistle is common in moist, acidic soils in New England  and Wisconsin .
In Europe, studies of soils in marsh thistle habitats suggest a wider tolerance of soil textures and pH levels than those evident from the few North American studies and sources available as of 2009. In southeastern Scotland, marsh thistle was most common on poorly to very poorly drained, acidic (pH 5-5.5), clay soils . In southwestern England, marsh thistle seedlings emerged from basic soil samples collected from a 45-year-old oak woodland but not from acidic soils collected from the same woodland . However, this study does not necessarily imply an establishment preference for basic soils and could simply be a result of uneven seed dispersal. In an old field in the Geescroft Wilderness area of England, marsh thistle occurred in damp, cool, acidic heavy loams but not in a field described as wet and alkaline . This finding could also be the result of dispersal and not preference. In the western part of the Utrecht Province in the Netherlands, marsh thistle was significantly (P<0.01) more frequent on ditch banks adjacent to fields fertilized with low levels of nitrogen (0-250 kg N/ha/year) than on fields fertilized with high levels of nitrogen (250-500 kg N/ha/year) . Marsh thistle emerged from all organic peat soil samples taken from a "recently" clearcut birch woodland in Germany. Soils were fed with calcium-rich groundwater .
Moist conditions are typical in marsh thistle's native habitats, but plants may not tolerate long-term flooding or saturation. In the coastal dune areas of the Netherlands, marsh thistle is common in oneseed hawthorn-European white birch woodlands where ground water occurs at or near the soil surface . In a spring area of Jutland, Denmark, marsh thistle plants did not grow in the wettest areas or on "regularly flushed" springs . Marsh thistle's drought tolerance is likely low. After a 3-month drought, leaves from marsh thistle plants growing in a species-rich, calcareous grassland in Derbyshire, England, had low relative water content. Of leaves of the 31 plant species evaluated, marsh thistle leaves were ranked 6th lowest in relative water content. Monthly precipitation during the drought averaged 43%, 84%, and 26% of long-term monthly averages .SUCCESSIONAL STATUS:
Shade tolerance: A weed fact sheet reports that marsh thistle is somewhat shade tolerant in North America . In Canada, marsh thistle populations tend to be replaced in late-seral, densely shaded forests, but "flourishing" populations have been reported in underbrush and "heavily canopied" sites (Minor and Nordin 2002 cited in ).
In Europe, marsh thistle is reported in shaded areas, although research suggests that reproduction and growth may be limited on shaded sites. During surveys of 4 river catchments in Wales, marsh thistle occurred in open and shaded damp sites throughout the study area . In Holmsley Bog in England, marsh thistle was frequent in the understory of mire vegetation where overstory species were up to 12 feet (3.7 m) tall . Cover of marsh thistle was generally low (1%) on floating peat woodlands at Westbroek Polder, Utrecht, the Netherlands . In the central Netherlands, marsh thistle seedlings were generally abundant in the 1st year after cutting in ash stands. Flower production was typically abundant in the 2nd year after cutting but decreased as time since cutting increased. Photosynthetically active radiation (PAR) transmission averaged 66.3% in the 1st year after cutting, 64.2% in 2nd year after cutting, and 2.5% in 4th year after cutting. On a 0.5-m² plot, there were 33 vegetative marsh thistles in 1st year after cutting. In the 2nd year after cutting, there were 5 vegetative and 5 flowering marsh thistles. Marsh thistle did not occur in the plots in the 3rd year after cutting .
Experiments suggest that marsh thistle growth and reproduction may be reduced by shading. In England, marsh thistle was grown in shaded cold frames that received 1%, 4.5%, 20%, and 90% PAR. All marsh thistle plants receiving only 1% PAR died within a year; plants getting 4.5% PAR produced leaf numbers and lengths that were about half those produced at 20% and 90%. Only those plants receiving 20% or 90% PAR flowered in their 2nd year. Experiments did not continue beyond the 2nd year of growth . In the Netherlands, marsh thistle leaf production, relative growth rate, and rosette dry-weight production all generally decreased with increased shading. Marsh thistle growth was monitored beneath 1.2%, 4.6%, 13%, 32%, and 100% of daylight . In constant 100% light, plants grew to about 5 feet (1.5 m), developed many branches, and produced abundant seed. Plants in constant 4.6% light, and plants transferred to 4.6% light after developing rosettes in 100% light, produced few branches and little to no seed. Most plants in 4.6% light had to be staked so that stems did not fall and break .
General succession information and disturbance response: Marsh thistle's place in the succession of woodlands and old fields is described in studies conducted in England. In the Wicken Fen in Cambridgeshire, marsh thistle generally persists throughout the succession from mixed-sedge vegetation to glossy buckthorn (Frangula alnus) dominance and eventual development of the oldest mire vegetation, dominated by common buckthorn (Rhamnus cathartica). Researchers noted marsh thistle could "persist thinly in a vegetative state" in the oldest mire . In the Geescroft area, marsh thistle was first recorded in an old field about 20 years after abandonment, when it was described as scarce; 30 years after abandonment it was described as occasional .
Based on studies in its native habitats, marsh thistle is generally more abundant on grazed than ungrazed areas. In Westerholt, the Netherlands, marsh thistle cover was greatest after the introduction of domestic sheep into common velvetgrass (Holcus lanatus)-dominated grasslands. Before domestic sheep grazing, the grassland was primarily harvested for hay, and marsh thistle cover was about 0.5%. Nine years after grazing, marsh thistle cover was 3.5% in lightly grazed areas, 3.2% on moderately grazed areas, and 2% on heavily grazed areas. Litter was greatest on the lightly grazed and least on the heavily grazed areas . When domestic sheep were removed from hill pastures in Snowdonia, South Wales, England, marsh thistle abundance decreased dramatically, and marsh thistle plants were restricted to steep, unstable ground. Researchers suggested marsh thistle in the steep areas may have established from seed produced on nearby grazed areas. Researchers indicated that the absence of gaps in the ungrazed turf canopy likely restricted marsh thistle reproduction . Although marsh thistle's spines suggest it would be avoided by herbivores, cattle in Tullgarn, Sweden, grazed plants .In a field experiment in a moist grassland on Harpur Hill in Derbyshire, England, disturbances increased marsh thistle abundance more than fertilization treatments. On control plots, the average cover of marsh thistle was 0.3%. On fertilized and undisturbed plots, the average cover of marsh thistle was 0.17%. Cover was 0.52% on unfertilized and disturbed plots and 0.56% on fertilized and disturbed plots. Disturbances were artificially created circular gaps with diameters of up to 4.7 inches (12 cm) and mechanically disturbed soil to depths up to 2 inches (5 cm). Plots were fertilized and disturbed twice before cover was estimated .
Fire adaptations and plant response to fire:
Fire adaptations: On sites with established marsh thistle plants, postfire sprouting from the root crown may occur. Because open sites are likely best for marsh thistle seedling emergence , burned areas could provide suitable establishment sites, given a seed source. See Germination and Seedling establishment and growth for more on these topics.
Plant response to fire: Studies documenting marsh thistle recovery, establishment, and increases or decreases in abundance on burned sites are lacking. Marsh thistle frequency was 9% in the aboveground vegetation in a "derelict", species-rich, tall herb community in northern England that was occasionally burned, although time since the last fire was not reported in this study. Marsh thistles seedlings did not emerge from soil samples collected from the site, although it emerged from soil samples collected in another lightly grazed but unburned vegetation type with similar aboveground marsh thistle frequency . Because this study was not designed to study marsh thistle's response, recovery, or reproduction on a burned site, findings presented here may or may not provide useful information on marsh thistle's postfire seed production.FUELS AND FIRE REGIMES:
Fire regimes: Marsh thistle is most common in moist to wet habitats (see Site Characteristics), where fires may be rare and/or burn with low severity. However, on sites with deep organic soils, fires may be infrequent but severe. Altered fire regimes in areas invaded by marsh thistle habitats were not reported. Fire studies in sites invaded by marsh thistle are needed.
See the Fire Regime Table for further information on fire regimes of vegetation communities in which marsh thistle may occur.FIRE MANAGEMENT CONSIDERATIONS:
Preventing postfire establishment and spread: Preventing invasive plants from establishing in weed-free burned areas is likely the most effective and least costly management method. This can be accomplished through early detection and eradication, careful monitoring and follow-up, and limiting dispersal of invasive plant seed into burned areas. General recommendations for preventing postfire establishment and spread of invasive plants include:
For more detailed information on these topics, see the following publications: [1,9,23,68].Use of prescribed fire as a control agent: There were no studies on the use of prescribed fire to control marsh thistle. While fire alone is unlikely to control marsh thistle, it could be useful in conjunction with other control methods. Fire could be useful in removing last year's stems and increasing plant exposure to other treatments. Fire may also be useful in the disposal of cut stems with seeds or flowers that could provide for reinvasion .
Control: Few studies provide guidelines for control of marsh thistle. Provided below are general guidelines and practices useful to the avoidance, control, and management of invasive species. When invasive species are targeted for control, there is potential for another invasive species to fill their void no matter what method is used . Often control of invasive species is most effective when a long-term, ecosystem-wide approach is used rather than a tactical approach focused on individual species control .
Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.
Prevention: Management practices that prevent the establishment of marsh thistle on uninvaded sites are considered best. Cleaning equipment used in marsh thistle populations before it enters uninvaded habitats is important in prevention (see Seed dispersal) .
Preventing establishment and spread of invasive species through the maintenance of "healthy" natural communities is often the most cost-efficient and effective management method [35,58]. Prevention methods could include avoiding new road construction in wildlands ) and consistent monitoring for invasive species . Managing to maintain the integrity of native plant communities and minimizing those practices that increase ecosystem invasibility will likely be more effective than managing solely to control the invader .
Weed prevention and control can be incorporated into land management plans, including site preparation and logging, grazing allotments, recreation management, research projects, road building and maintenance, and fire management . See the Guide to noxious weed prevention practices  for specific guidelines in preventing the spread of weed seeds and propagules during land management operations.
Physical or mechanical control: Hand-pulling of small marsh thistle populations may provide successful control . Mowing or cutting may provide control when done repeatedly or combined with other control methods. After 3 to 4 years of repeated mowing or cutting near ground level, the size of marsh thistle populations may decrease. If plants are cut when flowers are present, it is recommended that stems be destroyed . If plants are flowering at the time of mowing, most will sprout in the next growing season, often producing more seed than undisturbed plants .
Biological control: As of 2009, there were no insect biological controls released for control of marsh thistle. Many factors need to be considered when determining the agents for biological control and the potential release of biological controls. Refer to these sources: [72,82] and the Weed control methods handbook  for background information and important considerations for developing and implementing biological control programs.
Chemical control: Herbicides may be effective in gaining initial control of a new invasion or a severe infestation, but rarely are they a complete or long-term solution to weed management . For marsh thistle, herbicide applications on cut hollow stems may be more effective than those on intact plants .
See the Weed control methods handbook for considerations on the use of herbicides in natural areas and detailed information on specific chemicals. Herbicide use may be restricted in wetland areas, where marsh thistle is common .Integrated management: Integrating control methods could increase the effectiveness of individual methods and the management of invasive species populations; however, studies involving or discussing this type of management in marsh thistle populations were lacking in the available literature (2009).
|Fire regime information on vegetation communities in which marsh thistle may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models , which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Great Lakes Grassland|
|Mosaic of bluestem prairie and oak-hickory||Replacement||79%||5||1||8|
|Surface or low||20%||2||33|
|Great Lakes Woodland|
|Northern oak savanna||Replacement||4%||110||50||500|
|Surface or low||87%||5||1||20|
|Great Lakes Forested|
|Northern hardwood maple-beech-eastern hemlock||Replacement||60%||>1,000|
|Conifer lowland (embedded in fire-prone system)||Replacement||45%||120||90||220|
|Conifer lowland (embedded in fire-resistant ecosystem)||Replacement||36%||540||220||>1,000|
|Great Lakes floodplain forest|
|Surface or low||93%||61|
|Great Lakes spruce-fir||Replacement||100%||85||50||200|
|Surface or low||67%||500|
|Maple-basswood mesic hardwood forest (Great Lakes)||Replacement||100%||>1,000||>1,000||>1,000|
|Surface or low||89%||35|
|Northern hardwood-eastern hemlock forest (Great Lakes)||Replacement||99%||>1,000|
|Red pine-eastern white pine (frequent fire)||Replacement||38%||56|
|Surface or low||26%||84|
|Red pine-eastern white pine (less frequent fire)||Replacement||30%||166|
|Surface or low||23%||220|
|Great Lakes pine forest, eastern white pine-eastern hemlock (frequent fire)||Replacement||52%||260|
|Surface or low||35%||385|
|Eastern white pine-eastern hemlock||Replacement||54%||370|
|Surface or low||34%||588|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Northern coastal marsh||Replacement||97%||7||2||50|
|Eastern woodland mosaic||Replacement||2%||200||100||300|
|Surface or low||89%||4||1||7|
|Northern hardwoods (Northeast)||Replacement||39%||>1,000|
|Eastern white pine-northern hardwoods||Replacement||72%||475|
|Surface or low||28%||>1,000|
|Northern hardwoods-eastern hemlock||Replacement||50%||>1,000|
|Surface or low||50%||>1,000|
|Northeast spruce-fir forest||Replacement||100%||265||150||300|
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [25, 33].
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