Solanum Dulcamara

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Solanum dulcamara

INTRODUCTORY DISTRIBUTION AND OCCURRENCE BOTANICAL AND ECOLOGICAL CHARACTERISTICS FIRE EFFECTS AND MANAGEMENT MANAGEMENT CONSIDERATIONS APPENDIX: FIRE REGIME TABLE REFERENCES

INTRODUCTORY

AUTHORSHIP AND CITATION FEIS ABBREVIATION NRCS PLANT CODE COMMON NAMES TAXONOMY SYNONYMS LIFE FORM FEDERAL LEGAL STATUS OTHER STATUS

Photo by Steve Dewey, Utah State University, Bugwood.org

AUTHORSHIP AND CITATION: Waggy, Melissa A. 2009. Solanum dulcamara. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ 2010, February 1].

FEIS ABBREVIATION: SOLDUL

NRCS PLANT CODE [163]: SODU

COMMON NAMES: bittersweet nightshade bitter nightshade bittersweet climbing nightshade European nightshade

TAXONOMY: The scientific name of bittersweet nightshade is Solanum dulcamara L. (Solanaceae) [90,122]. Two varieties are recognized in North America: Solanum dulcamara L. var. dulcamara [90,147] Solanum dulcamara L. var. villosissimum Devs. [90,122,146,147]

SYNONYMS: None

LIFE FORM: Shrub-vine

FEDERAL LEGAL STATUS: None

OTHER STATUS: Information on state-level noxious weed status of plants in the United States is available at Plants Database.

DISTRIBUTION AND OCCURRENCE

SPECIES: Solanum dulcamara

GENERAL DISTRIBUTION HABITAT TYPES AND PLANT COMMUNITIES

GENERAL DISTRIBUTION: Bittersweet nightshade is a nonnative species in North America that has been introduced throughout many parts of Canada and the United States. According to Plants Database, it occurs in all conterminous states except Arizona, Texas, Arkansas, Louisiana, Mississippi, Alabama, and South Carolina [163]. A single specimen was observed at a residence in Arizona in 1989 [145]. In Canada, bittersweet nightshade occurs in all provinces except Alberta and Manitoba and has not been reported in the northern territories [163]; its northern limit in North America was reported to be near 46°N [152]. In the United States, bittersweet nightshade is reported to be most common in the eastern and north-central United States (review by [164]), and widespread in the upper Great Lakes states (review by [28]) and the Pacific Northwest (reviews by [93,125,126]). Plants Database provides a distributional map of bittersweet nightshade and its varieties in the United States and Canada.

Bittersweet nightshade is native to Europe from central Norway, south to northern Africa, and east and central Asia ([57,74], reviews by [53,183]). As a result of its introduced range, bittersweet nightshade is considered to have a circumpolar distribution [84]. Bittersweet nightshade has also been introduced to Peru [13], New Zealand, and Australia ([87], review by [126]).

Probable causes of bittersweet nightshade introduction to North America are cultivation by early settlers (reviews by [53,117,183]) and agricultural and shipping activities in the Pacific Northwest [51,52]. The earliest reports of bittersweet nightshade's establishment outside of cultivation in North America are from the Great Lakes region, where it occurred by the mid-1800s ([169], Wisconsin State Herbarium 2006 as cited in [126]). Floras and surveys indicate that bittersweet nightshade spread to parts of the eastern and western United States by the early 1900s [73,109,144,175].

HABITAT TYPES AND PLANT COMMUNITIES: Although bittersweet nightshade has not been studied in North America for its associated plant communities, a sufficient amount of incidental information is available to provide a broad description of its typical associates in North America. Throughout its introduced range, bittersweet nightshade most frequently occurs in riparian areas, wetlands, and deciduous forests, but occasionally occurs in open habitats such as grasslands and meadows in the Great Lakes region. It typically occurs as a minor component in most plant communities but may be relatively abundant in riparian areas. Bittersweet nightshade's occurrence is often associated with previous or ongoing anthropogenic disturbance.

Eastern North America and Great Lakes region: In eastern North America and the Great Lakes region, including southern Ontario, bittersweet nightshade is often associated with riparian and deciduous forests. Riparian communities in these areas are often characterized by maple (Acer spp.) overstories with a mix of other deciduous trees such as pin oak (Quercus palustris), ash (Fraxinus spp.), cherry (Prunus spp.), basswood (Tilia americana), or American elm (Ulmus americana) [3,27,45,71,79,83,116,121,157,166]. Bittersweet nightshade also occurs on sites dominated by eastern cottonwood (Populus deltoides) [116] that may contain a mix of sycamore (Platanus occidentalis) and American elm [83]. Bittersweet nightshade occurs in upland mesic deciduous forests with a similar composition of overstory species and with other deciduous trees that may be more characteristic of mesic sites such as American beech (Fagus grandifolia), northern red oak (Quercus rubra), and slippery elm (Ulmus rubra) [10,11,27,35,45,85]. In one study, bittersweet nightshade commonly occurred in an eastern hemlock- (Tsuga canadensis) dominated forest [83], and it may occur in coniferous forests dominated by northern whitecedar (Thuja occidentalis) in Canada [11,35].

Bittersweet nightshade also occurs in open plant communities in eastern North America and the Great Lakes region. It occurs in a variety of wetland plant communities often dominated by cattail (Typha spp.) [3,4,67,77,157,165], sedge (Carex spp.) [26,157,165], Olney threesquare (Scirpus americanus) [30], or alder (Alnus spp.) [3,83]. It occurs in wetlands with other nonnative or invasive species such as purple loosestrife (Lythrum salicaria) [3,30,67,77,129] and reed canarygrass (Phalaris arundinacea) [3,77,148]. In the Great Lakes region, bittersweet nightshade occurs in a number of characteristically open plant communities. In northern Illinois bittersweet nightshade occurs in calcareous wet places with yellow marsh marigold (Caltha palustris), common boneset (Eupatorium perfoliatum), field horsetail (Equisetum arvense), and other species associated with this type of habitat. In southeastern Wisconsin, it occurred in mesic tussock sedge (Carex stricta) meadows [26]. In southeastern Minnesota, bittersweet nightshade was more often associated with wetlands with low plant density and tall vegetation. It was also more commonly associated with wetlands characterized by narrow-leaf cattail than those characterized by purple loosestrife [67]. In northern Illinois and east-central Minnesota, bittersweet nightshade occurred with bur oak (Quercus macrocarpa) and northern pin oak (Quercus ellipsoidalis) in a remnant oak savanna [12] and in an oak forest where fire had been reintroduced over the last 20 years in an attempt to restore the site to a savanna [160]. At Indiana Dunes National Lakeshore it occurred in an oak savanna with black oak (Quercus velutina) along with a rich understory of forbs and abundant grasses [107].

Western North America: Information pertaining to bittersweet nightshade's occurrence in western North America comes primarily from the northwestern United States. Bittersweet nightshade occurs in riparian areas ([46,47,101,112,137], reviews by [93,125]) and is most commonly associated with cottonwood (Populus spp.) [23,46,47], native willow (Salix spp.), and alder [16,23,32,68]. It often occurs on disturbed sites with other nonnative or invasive species including eggleaf spurge (Euphorbia oblongata), Canada thistle (Cirsium arvense), common St. Johnswort (Hypericum perforatum), Himalayan blackberry (Rubus discolor) [68], Russian-olive (Elaeagnus angustifolia), tamarisk (Tamarix spp.) [16,32], and reed canarygrass [46,47]. In western Montana, bittersweet nightshade was one of the 15 most abundant plants (0.1% - 2.0% average cover) in a riparian area invaded by Norway maple (Acer platanoides) [137].

As of 2009, little published information is available regarding bittersweet nightshade's distribution in western North America outside riparian areas. One study in California found bittersweet nightshade on 1 plot (n=1,543) on a fuel break in an oak woodland [118].

Native range: Information pertaining to bittersweet nightshade's associates in its native range comes primarily from the United Kingdom, where it occurs in open woodlands or shrublands that are often associated with moist environments. Bittersweet nightshade occurs on maritime-influenced sand dunes dominated by willows and other shrubs where it comprises 1% to 40% of the vegetation cover. In one sand dune community characterized by stinging nettle (Urtica dioecious), bittersweet nightshade cover can range between 41% and 60%. In open habitats prone to weed invasion, bittersweet nightshade cover can range from 41% to 60%, and it is most common on sites characterized by common reed (Phragmites australis) [57,143]. It commonly occurs in willow and alder thickets and reaches its greatest cover (61% to 80%) in an alder woodland community characterized by common reed [141]. Bittersweet nightshade occurs in a rush- (Juncus spp.) dominated meadow fen where it can comprise 1% to 20% of the vegetation cover [142]. In England, bittersweet nightshade commonly occurs in woodlands dominated by birch (Betula spp.), glossy buckthorn (Frangula alnus), willow, viburnum (Viburnum spp.), ash, pine, and oak [61]. In early successional European beechwood (Fagus sylvatica) communities it occurs in scrubland dominated by hawthorn (Crataegus spp.) and cherry, and with common juniper (Juniperus communis spp.) and English yew (Taxus baccata) on calcareous soils and exposed sites [171]. In central Europe, bittersweet nightshade occurs in floodplain habitats dominated by willow, cottonwood, elm, oak, and alder [37,43,57]. In Hungary, bittersweet nightshade occurs in marshes, fens, and other types of wetlands (Soo 1968 cited in [14]). In parts of Germany, bittersweet nightshade occurs in scrubland and woodland [58,76,96].

Other: In New Zealand, bittersweet nightshade occurred after fire in a dry, gorse- (Ulex europaeus) dominated bog [87].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Solanum dulcamara

GENERAL BOTANICAL CHARACTERISTICS SEASONAL DEVELOPMENT REGENERATION PROCESSES SITE CHARACTERISTICS SUCCESSIONAL STATUS

©Gerald D. Carr, Oregon Flora Image Project

GENERAL BOTANICAL CHARACTERISTICS:

Botanical description Raunkiaer life form

Botanical description: This description provides characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [60,64,78,112,122,181]. Above ground: Bittersweet nightshade is a perennial, rhizomatous [60,64,78,101,131] vine or scrambling shrub. Its base is woody, and the aboveground branches are herbaceous and die back each year. Aboveground stems are typically about 10 feet (~3 m) long [60,78,174], sometimes growing as long as 23 feet (~7 m) (review by [53]). Bittersweet nightshade's stems can twine over other plants, trail along the ground, or grow erect (reviews by [126,164]). Its leaves vary from about 2 to almost 5 inches (5-12 cm) long. Its inflorescence is a drooping cyme [64,112,174] or panicle [64,134], typically having 7 or more flowers, sometimes as many as 30 [60,64,134]. Its fruit is a berry, 2 to 8 mm in diameter ([64,112,174], reviews by [66,182]). Bittersweet nightshade seeds are 2 to 3 mm x 1.7 to 2.5 mm and are strongly flattened (reviews by [66,164,183]).

Below ground: Bittersweet nightshade spreads by rhizomes [60,64,78,101,131]. The main root grows horizontally just below the soil surface, sprouts frequently (review by [53]), and can branch 3 to 5 times [18]. Roots of bittersweet nightshade have secondary growth and an epidermis that is protected by a layer of suberin at the root cap. Feeder roots are 100 to 500 µ in diameter and sprout root hairs that grow up to 400 µ [18].

Brundrett and Kendrick [18] determined that the roots of bittersweet nightshade can be colonized by mycorrhizal fungi, albeit poorly, and classified bittersweet nightshade as facultatively mycorrhizal. Species classified as facultatively mycorrhizal may benefit from a mycorrhizal association but are not dependent on it (Janos 1980, cited in [18]).

Population structure: Plants grow singly or in dense patches, often taking advantage of structural support (i.e., trees, shrubs, fences) to reach more light (reviews by [93,164]). Bittersweet nightshade may be a dominant species on some sites ([22,46,137,166], review by [125]), form small, near monocultures (review by [125]), or be locally abundant (review by [126]) in riparian areas and other moist habitats, especially in New England [22,166], the mid-Atlantic states (review by [126]), the Great Lakes states (reviews by [125,126]), and the Pacific Northwest ([46,47], reviews by [125,137,166]).

Allelopathy: Water extract from the foliage of bittersweet nightshade significantly inhibited some aspects of growth in red pine (Pinus resinosa) seedlings, suggesting allelopathic properties. Red pine seedlings treated with the extract exhibited a decrease in the production of secondary needle fascicles and a significant decrease in shoot weight (P<0.05) and radicle elongation (P<0.001) [128]. As of this writing (2009), however, allelopathy in bittersweet nightshade has not been studied in the field.

Raunkiaer [135] life form: Chamaephyte Hemicryptophyte

SEASONAL DEVELOPMENT: In the spring, new branches of bittersweet nightshade grow from the woody base, spreading horizontally or climbing over other vegetation or structures ([150], review by [93]). Flowering period for bittersweet nightshade can be somewhat variable across its range but typically occurs throughout most of the growing season:

Reported flowering and fruiting periods for bittersweet nightshade by geographic area Area Flowering and/or fruiting periods North America Carolinas June-September [134] Florida June-September [181] Illinois late May-October [122,157] Nevada May-September [91] New York August [34] West Virginia June-September [155] Adirondack Mountains flowers June; fruits September [100] Blue Ridge Province May-September [177] Great Plains May-September [64] New England flowers May-September, fruits July-October [117] North America (general) May-September (review by [59]) North America (general) flowers July-August; fruits July-October (reviews by [182,183]) Northeastern United summer-fall [60] States Pacific Northwest May-September [78] Canada (Ontario) June-August or later [152] Other Countries China flowers summer; fruits fall [180] England (Warwick) fruiting through October [139] Germany fruiting begins June - July [98] Pakistan June - July [2] Sweden flowers mid-June to July; fruits late August-September [44]

In North America, bittersweet nightshade berries are produced throughout summer and fall and may remain on the plant until winter (reviews by [59,182,183]). In the United Kingdom and parts of Germany, its berries may begin ripening toward the end of July, are most abundant between August and late September/early October [9,37], and may continue to be produced through at least early November [9]. In Sweden, bittersweet nightshade fruit persists on the vine for an average of about 20 days [44]. Bittersweet nightshade's branches from the current year die back 3 to 9 feet (1-3 m) or more (review by [53]) to the woody base each winter ([150], review by [183]). Germination tests indicate that most bittersweet nightshade seedlings emerge in spring (see Germination).

REGENERATION PROCESSES: Bittersweet nightshade reproduces by seed and locally through vegetative regeneration.

Pollination and breeding system Seed production Seed dispersal Seed banking Germination Seedling establishment and plant growth Vegetative regeneration

Pollination and breeding system: Flowers of bittersweet nightshade are perfect [184], and information pertaining to self compatibility is lacking. Stamens have short filaments and long lance-shaped anthers which fit closely around the style. Stamens dehisce from a pore at the top releasing pollen [69,158]. Primary pollinators of bittersweet nightshade are bumblebees [54,69,158]; occasional pollinators include solitary bees, sweat bees, and syrphids flies [158]. In Canada, Liu [108] found that various species of bumblebees visited bittersweet nightshade flowers between June and August.

Flower and seed production: Bittersweet nightshade plants in full sun or light shade may produce more flowers and fruits than those in moderate to medium shade (review by [53]). Seed production is generally considered "high" in bittersweet nightshade [150]. Fruits of bittersweet nightshade contain 40 to 60 seeds each (reviews by [66,183]); however, one review [53] indicated that the average number of seeds per fruit may be fewer (31 seeds/fruit). One study from Sweden found that fruits contained fewer seeds on average (19.5 seeds/fruit) than what has been reported in North America [44].

Seed dispersal: Bittersweet nightshade seeds are dispersed primarily by birds [76,97,98,150,154,155,175]. Birds consume the fleshy fruit, digest the pulp, and spread undamaged seeds by regurgitation or defecation [76,98]. In eastern states and the Great Lakes region, most bittersweet nightshade fruits were eaten and seeds dispersed shortly after fruits ripened in July and August [150,154]. Birds continued to forage on bittersweet nightshade fruit into the fall but to a lesser extent than in summer [150]. Mammals also eat bittersweet nightshade fruit and disperse its seed [124,155,156]. In eastern North America, Myers and others [124] concluded that white-tailed deer eat the fruit of bittersweet nightshade and have the potential to aid in the long distance distribution of its seed. See Importance to wildlife and livestock for more information on animals that eat bittersweet nightshade fruit and seeds.

Seed rain (i.e., all seeds arriving at a site through various dispersal mechanisms) from bittersweet nightshade can be highly variable and may be influenced by habitat, site characteristics, or annual fluctuations in seed production or bird populations [11,98,150]. In Ontario, bittersweet nightshade mean seed rain over a 2-year period was significantly higher (P<0.1) on cliff faces than on the adjacent plateaus above the cliffs or in talus at the base of the cliffs. Greatest seed rain density for any one site in a given year occurred on talus. Bittersweet nightshade seed rain was greater in the 1st year of the study than the 2nd for all 3 site types [11], but reason for this variability was not reported.

Mean bittersweet nightshade seed rain density (seeds/m²) for three habitats in Ontario, over a 2-year period [11] Year Sites 1993 1994 Plateau Milton 0 0 Dufferin 16 0 Cliff face Milton 217 57 Dufferin 469 36 Talus Milton 609 0 Dufferin 0 0

In a jack pine (Pinus banksiana) plantation forest in Illinois, Smith [150] used seed traps during the summer and fall over a 2-year period to estimate bittersweet nightshade's total seed rain. Average seed rain for the first year was about 4 seeds/m², compared to about 12 seeds/m² the following year. Many of the other species collected also had greater seed rain in the 2nd year, leading researchers to speculate that the difference between years was likely due to increased seed set and/or larger bird populations [150].

In western Germany, seed rain was collected across various habitats for 1 year. Average seed rain for bittersweet nightshade was about 0.2 seeds/square foot. Approximately half were dispersed from primary sources (intact fruit dropped due to ripening) and the other half from secondary sources (regurgitated or defecated by birds) [98].

Seed banking: Research pertaining to the longevity, density, and vertical distribution of bittersweet nightshade seed in the soil seed bank is limited, and much of the information discussed below has been derived from germination studies conducted in controlled environments. Additional research is needed to more accurately characterize bittersweet nightshade's seed banking potential for wild populations.

Results of germination tests from North America and Europe suggest that bittersweet nightshade seed may have a transient seed bank or one that persists for only a short time. Some bittersweet nightshade seeds germinate shortly after dispersal while most other viable seeds tend to germinate by the following spring [1,119,138,139,150]. In germination tests, 62% to 80% of bittersweet nightshade seeds germinated within 1 year after planting outdoors [1,138]. In the laboratory, over 90% of bittersweet nightshade seeds germinated within 15 days. Seeds used in this experiment had their seed coats manually broken prior to experimentation and were grown in petri dishes that were exposed to adequate moisture, light, and temperature [119]. Approximately 80% of bittersweet nightshade seeds placed in dry storage for over 12 months germinated in an incubator with alternating temperatures [139], suggesting that bitterroot nightshade seeds may stay viable for longer than a year under some conditions.

Reported densities of viable bittersweet nightshade seed in the soil are low [17,94]. At Indiana Dunes National Lakeshore, researchers [107], using the seedling emergence method, estimated bittersweet nightshade average seed densities in an oak savanna to be 6 seeds/m² for soil samples collected to a depth of 4 inches (10 cm). Another study from southern Canada also used the seedling emergence method and estimated the average density of germinable bittersweet nightshade seeds in the soil seed bank to be less than about 3.4 seeds/m² from soil samples collected to a 4- inch (10 cm) depth in a deciduous forest. In that same study, researchers used the seed extraction method, which counts viable as well as non-viable seed, to estimate bittersweet nightshade seed density in the same forest. Density estimates obtained using the seed extraction method were higher (91 seeds/m²) than for those obtained using the seedling emergence method, suggesting that most bittersweet nightshade seeds in the soil were not viable [17].

Studies on bitterroot nightshade's soil seed bank often lack detailed information about its occurrence in the aboveground vegetation [17]; however, available evidence suggests that bittersweet nightshade seed density in the soil seed bank is minimally influenced by its abundance in the aboveground vegetation [11,33,71,77]. In Ontario, Canada, Booth and Larson [11] found no relationship between bittersweet nightshade's aboveground vegetation cover and seed rain for 3 different habitats. In Pennsylvania, seedlings of bittersweet nightshade did not emerge from any of the sampled plots (n=110), even though 2.1% of the plots contained bittersweet nightshade in the aboveground vegetation [71]. In the Great Lakes region, a small amount (0.14% mean cover) of bittersweet nightshade occurred in coastal wetlands that had been diked; however, it was not present in the seed bank [77]. In Great Britain, viable bittersweet nightshade seed was found in the soil seed bank, although it did not occur in the aboveground vegetation [33]. Two studies indicated that bittersweet nightshade occurred in both the aboveground vegetation and seed bank; however, abundance was not reported for either [105,107].

Germination: Information pertaining to germination of bittersweet nightshade comes primarily from reviews and germination tests performed in the laboratory, or controlled experiments conducted outdoors. In North America, freshly collected bittersweet nightshade seeds are generally considered to have a "high" germination capacity ([150], reviews by [182,183]). A review indicated that when germinated under light, 61% to 98% of bittersweet nightshade seed germinated without stratification (review by [53]). In Illinois, fresh seeds grown in an outdoor experimental plot had a relatively high estimated probability of germination (0.845) [150]. Bittersweet nightshade seeds typically germinate between March and April [138,139], but some are capable of germinating during the growing season in which they are produced [138,139,150].

Warm diurnal temperature regimes may provide optimal germination conditions for bittersweet nightshade seed. In controlled environments, fresh bittersweet nightshade seed germination rates were high at alternating temperatures in the range of 68 to 95 °F (20 -35 °C), lower at constant temperatures of 77 to 95 °F (25-35 °C), and no germination occurred at temperatures below 68 °F (20 °C) [65,131,138,139]. One laboratory study obtained over 90% germination of bittersweet nightshade seed exposed to constant temperatures between 68 to 77 °F (20 -25 °C) [119].

Cold stratification of bittersweet nightshade seed may increase germination under some circumstances but does not appear to be a requirement [1,119,138,139]. It may allow for germination of bittersweet nightshade seed at lower temperatures than fresh seed or act as a substitute for exposure to light or warmer temperatures [65,131].

Bittersweet nightshade seeds germinate in light and dark ([65,119,131,150], reviews by [53,183]), and there appears to be no light requirement during burial [65,139]. In the laboratory, Mitchell [119] obtained over 90% germination of bittersweet nightshade seeds exposed to either dark or light at constant temperatures. In an outdoor experimental plot, nearly 50% more seeds germinated in light versus shade, but mortality was lower for seedlings germinating in shade [150]. Another laboratory study found that seeds of bittersweet nightshade germinated well in light or dark when exposed to alternating temperatures; however, germination was greater for seeds grown in dark at constant temperatures [131].

Seedling establishment: Although germination tests suggest that germination rates for bittersweet nightshade may be high (see Germination), seedling mortality may also be high. A study in Illinois found that seedlings of bittersweet nightshade had a relatively high estimated probability of finding a safe site for establishment (0.683) and were not as susceptible to predation as other species it occurred with [150]. However, first-year survival rates for bittersweet nightshade seedlings may be less than 10% [97,150]. Seedlings establishing in shade may have greater survivability. Bittersweet nightshade seedlings establishing in the sun had a 5% higher mortality rate than those establishing under tree canopy [150]. Illustrations of early seedling development of bittersweet nightshade are available in seed manuals: [182,183].

Plant growth and physiology: As of this writing (2009), no specific information is available pertaining to bittersweet nightshade's growth rate; however, Smith [150] indicated that once bittersweet nightshade becomes established it is capable of "rapid" growth across the forest floor and up into trees.

Bittersweet nightshade's morphology [25,50,82], biochemistry [25,57], and physiology [24,25,50,57] can be altered with varying degrees of water [24,25], light [25,57,82], CO2 [50], and temperature [24,25,50]. In the laboratory, leaves from bittersweet nightshade plants grown in sun were thicker and contained less chlorophyll by weight (mg Chl/g of leaf) than leaves on plants grown in low light [25]. In another laboratory experiment, elevated temperatures increased plant height and net photosynthesis [50]. Clough [25] concluded changes in light may have influenced bittersweet nightshade's phenotype and photosynthetic rate more than changes in water and temperature. Based on laboratory studies, researchers in Germany and Hungary have suggested that bittersweet nightshade has several ecotypes with varied tolerance to sun or shade [57,82]. In contrast, researchers in Illinois suggest no ecotypic differentiation with respect to light and shade environments. Bittersweet nightshade collected from shade and full sun environments was able to occupy a full range of light levels through phenotypic plasticity rather than ecotypic differences [24,25]. See Successional status for more information about shade tolerance of bittersweet nightshade.

Vegetative regeneration: Bittersweet nightshade spreads vegetatively by creeping stems that root at the nodes ([150], reviews by [53,164]) and by rhizomes [60,64,78,101,131]. It sprouts from the base when cut or damaged (review by [53]). Root and stem cuttings can be used for vegetative propagation ([58,89], reviews by [53,183]).

SITE CHARACTERISTICS: General Climate: Bittersweet nightshade occurs in areas with a mean July temperature of about 72 °F (22 °C) [3,23,85], but it and can also establish in areas with warmer subtropical climates like Florida [181] that experience average July temperatures around 81°F (27 °C) [179]. Bittersweet nightshade tolerates dormant-season temperatures below freezing ([3,23,85], review by [53]). It commonly occurs in regions of North America that receive moderate annual precipitation from about 32 to 45 inches (810-1,140 mm) [34,85] but also occurs in subtropical climates and in maritime-influenced regions of the Pacific Northwest, where annual precipitation is greater [179]. Bittersweet nightshade also occurs in semi-arid climates of the Pacific Northwest [23,137], where annual precipitation can be as low as 9.6 inches (244 mm) [23].

Habitat and moisture: Bittersweet nightshade commonly occurs in habitats associated with water, such as riparian areas [23,32,46,71,79,113,121], marshes [30,89,112,122,148,169], wetlands [4,41,63,67,83,123,166], lake shores ([112], review by [53]), forested freshwater dune barriers [10], pond edges [45,169], and canal banks [174]. Bittersweet nightshade also occurs in moist thickets [64,78,122,169,178], mesic deciduous woods [45,85,99,169], and clearings [60,78,91,169]. In eastern and Great Lakes states, sparse amounts of bittersweet nightshade occasionally occur in open habitats such as remnant prairie and grasslands [7,167], moist savanna [12,122], and mesic tussock meadow [26].

Bittersweet nightshade appears to be most abundant in riparian habitats. In western New York, bittersweet nightshade was a subdominant species in swampy woodland and its edges [166]. Along the Snake River in Idaho, bittersweet nightshade was present in 60% of sampled sites (n=40) [32]. Bittersweet nightshade occurred in 82% of the 28 black cottonwood (Populus balsamifera var. trichocarpa)-dominated riparian forests sampled along the Willamette River in Oregon [46]. In western Montana, bittersweet nightshade was one of the most abundant plants (0.1-2.0% average cover) observed along a portion of Rattlesnake Creek that had been invaded by Norway maple. It was more abundant on sites where Norway maple cover was relatively low and species diversity was greater [137].

Available literature from North America indicates that bittersweet nightshade can tolerate some flooding and sites inundated with water [3,45,63,71]. The national wetland indicator status for bittersweet nightshade in most regions where it occurs in the United States is "Facultative", indicating that it has an estimated 34% to 66% probability of occurring in a wetland, and is just as likely to occur in a wetland as a non-wetland. In north-central states such as North Dakota, South Dakota, and eastern Montana, bittersweet nightshade usually occurs in non-wetland sites and only has a 1% to 33% chance of occurring in a wetland [163]. In Pennsylvania, bittersweet nightshade occurred in 2.1% of plots that were infrequently flooded but did not occur in plots with frequent to moderate flooding [71]. In another study in Pennsylvania, bittersweet nightshade was strongly associated with the presence of seasonal surface water in relatively undisturbed wetlands [63]. Bittersweet nightshade occurred in and near a series of ponds located in 2 lowland deciduous forest woodlots in Ontario, Canada. It commonly occurred in continually flooded areas and the surrounding forest and was considered to be a wet-mesic species in temporarily flooded areas [45]. In Massachusetts, bittersweet nightshade was found growing in over 1.5 feet (0.5 m) of standing water in a shrub swamp associated with a small stream [3]. One floristic survey from Fire Island Seashore National Park in New York described bittersweet nightshade as favoring dry disturbed sites [34], suggesting that bittersweet nightshade may also tolerate dry conditions.

In its native range, bittersweet nightshade is associated with a wide range of habitats [14,57]; however, it maintains a strong affiliation with wet and waterlogged habitats such as seashores, river banks, floodplains, swamps, canals, ditches, mires, damp woods ([43,131], review by [55]), and marshes [14,57,58]. In Europe it is considered a species characteristic of alder fens that occupy "extremely wet ground" where most deciduous woodland plants cannot survive [43], and it is an indicator species of moist to waterlogged habitats that may be inundated throughout the year ([43], Ellenberg 1979 as cited in [131]). It occurs in coastal dunes [9,57], thickets, forest edges, forest clearings, hedgerows, and "waste ground" [131]. It can also occur on dry sites within portions of its native range [58,86]. In central Germany, bittersweet nightshade occurred on open, fully exposed locations in low-growing, xerophytic shrublands [58]. A small amount of bittersweet nightshade was also found growing on a sparsely vegetated magnesium limestone cliff face in Sheffield, England [86].

Disturbance: In North America, bittersweet nightshade appears to prefer sites where the natural vegetation has been altered, such as human developments, roadsides, fence rows, gardens, airstrips, and around buildings [7,34,91,112,130,134,155,167,169,174,181]. Undeveloped sites are also susceptible to invasion by bittersweet nightshade, but its occurrence on these sites is typically associated with disturbance ([130], reviews by [28,117,126]). In southern Manitoba, bittersweet nightshade was considered an indicator of disturbance (e.g., social trails, garbage) in an urban riparian forest along the Assiniboine River [120,121]. Its occurrence in wetlands is often associated with some type of disturbance or water level change such as a dike [77], an abandoned limestone quarry [4], or an abandoned municipal dump [140]. Ongoing or previous grazing has also been associated with bittersweet nightshade occurrence [23,32,105].

Bittersweet nightshade may occasionally establish in undeveloped, relatively undisturbed native plant communities ([35,130,136,157], reviews by [28,93,126]). A review by NatureServe [126] suggests that riparian areas, wetlands, deciduous forests, and grasslands may be at risk from invasion by bittersweet nightshade. Invasive plant surveys from Wisconsin indicated that, although bittersweet nightshade may be more commonly associated with disturbance, it occasionally occurs in wetlands, forests, and grasslands on sites where the ground has not been recently disturbed [136]. Field observation in Illinois occassionally found bittersweet nightshade in native plant communities with relatively little disturbance [157]. In Washington, bittersweet nightshade can occur in relatively undisturbed riparian areas and wetlands (review by [93]). An analysis by Parks and others [130] indicated that most vegetation cover types common to the mountain ecoregions of the northwestern United States are susceptible to invasion by bittersweet nightshade when the vegetation is disturbed, but bittersweet nightshade may invade riparian areas in the absence of disturbance.

Elevation: Information pertaining to bittersweet nightshade's elevational range is patchy. Information from a few regional floras and publications suggests it occurs in a wide range of elevations, from near sea-level along the coasts to over 7,000 feet (2,134 m) in the western United States ([7,16,71,85,91,130,145,174], review by [133]). Available information suggests that bittersweet nightshade occurs at higher elevations in its native range [2,74,84,180].

Reported elevational ranges for bittersweet nightshade North America Location Elevation Arizona 6,900 feet (2,103 m) [145] Idaho 2,723 to 3,018 feet (830-930 m) [16] Minnesota 1,600 feet (490 m) [7] New England 5 to >1,000 feet (1.5-305 m) (review by [117]) New York 460 to 690 feet (140-210 m) [85] Nevada 4,000 to 4,600 feet (1,219-1,402 m) [91] North Carolina, Craggy Mountains* 2,395 to 6,684 feet (730-2,037 m) [114] Pennsylvania 985 to 1,312 feet (300-400 m) [71] Utah 4,364 to 7,119 feet (1,330 - 2,170 m) [174] Northwestern mountain states ** all elevations [130] Pacific Northwest, coast low elevations (review by [133]) Other Countries Alps 5,577 feet (1,700 m) [84] China 1,640 to 11,483 feet (500 - 3,500 m) [180] India and Pakistan 3,937 to 9,186 feet (1,200 - 2,800 m) [2,74] *The base-level for most streams in the Craggy Mountains is 3,690 feet (1,100 m) and is the habitat where bittersweet nightshade would likely occur [114]. **Oregon, Washington, Idaho, and western Montana [130].

Substrate: Bittersweet nightshade occurs in a variety of soil types and textures [26,27,30,41,45,105,121,137,150]. Bittersweet nightshade commonly occurred on Penobscot Bay in Maine, in shallow soils consisting mostly of humus [22]. In New Jersey, bittersweet nightshade was more likely to occur on sites with higher percentages of sand [41]. In Montana, bittersweet nightshade commonly occurred in a riparian deciduous forest characterized by deep, well drained, gravelly loam (Anonymous 1995, cited in [137]). A review [55] indicated that in Europe, bittersweet nightshade occurs in rich loam and clay.

Bittersweet nightshade occurs on sites with a range of soil pH. Studies from Illinois [4], Wisconsin [26], Manitoba [121], and Idaho [32] report the occurrence of bittersweet nightshade on soils with pH ranging from 7.2 to 8.29. In a riparian area along the Snake River in Idaho, bittersweet nightshade was a dominant species and was most common near seeps with average pH of 8.27 [32]. Additional information suggests that bittersweet nightshade can tolerate lower pH. In New York [83] and Ontario [30,45], bittersweet nightshade occurred on sites with soil pH ranging from 5.2 to 7.2. A review grouped bittersweet nightshade with plants considered "alka-tolerant". Species in this group required pH ranges above 4.8 to 5.2 and were tolerant of pH levels as high as 7.9 to 9 [149].

Bittersweet nightshade may prefer soils rich in nitrogen. On the Snake River in Idaho, bittersweet nightshade was most dominant on sites associated with relatively high average nitrate levels (39.54 ± 8.32 ppm) [32]. One study from Massachusetts found bittersweet nightshade to be an indicator of low carbon to nitrogen ratios in the soil following high intensity tree harvesting [115]. In Europe, bittersweet nightshade is typically found in basic soils on sites rich in nitrates such as floodplains and thickets [43]. In the Netherlands, bittersweet nightshade is found in a range of substrates, from mineral soils to organic soils (peat) rich in nitrogen (Ellenberg 1979 cited in [131]). SUCCESSIONAL STATUS: Researchers in the field have observed bittersweet nightshade in various successional stages [5,12,46,87,123] and in a wide range of light levels [24,57,58], suggesting that it may establish and persist in a range of successional stages, from early to late succession. It may, however, fail to adapt to rapid increases in light where it is established in shade; rapid canopy removal may lower its productivity and inhibit its growth [57,92].

Shade tolerance: Bittersweet nightshade occurs in habitats ranging from full sun to deep shade in both its native European [57,58] and nonnative North American ranges [24]. Research has been conducted (see Plant growth and physiology) to determine if bittersweet nightshade's ability to grow in a full range of sun and shade habitats is genetic or phenotypic in origin [24,25,57]. Some evidence indicates that bittersweet nightshade is more likely to persist and spread on open or lightly shaded sites, while other evidence indicates a preference for shade. A review suggests that bittersweet nightshade plants in full sun or light shade produce more flowers and fruit than those in moderate to medium shade [53]. While seedlings of bittersweet nightshade may be shade tolerant and able to survive and grow under a moderate forest canopy ([150], review by [117]), bittersweet nightshade's productivity [24,25] and abundance [5,85] may decline with increased shade on some sites (see Potential successional stages). Conversely, data collected in a moist savanna remnant in Illinois suggest that bittersweet nightshade is more tolerant of shade than full sun in these communities. Bittersweet nightshade frequency was highest (25% and 22.9%) in plots with canopy shade and a mean photosynthetically active radiation (PAR) of approximately 143.1 and 164.7 mol/m²/s, respectively. Bittersweet nightshade frequency was 3.0% on plots with mean PAR of about 490.7 mol/m²/s, and it did not occur in canopy-gaps with a mean PAR of about 826.6 mol/m²/s [12]. Bittersweet nightshade's ability to take advantage of available light through alterations in morphology, biochemistry, and photosynthetic rates may facilitate its ability to grow in shade (see Population structure and Plant growth and physiology).

Potential successional stages: Bittersweet nightshade often occurs on disturbed sites where moisture is adequate (see Site Characteristics) and has been noted in early stages of succession after wildfire in New Zealand [87] and on old fields in the central United States [123]. In New Zealand, where bittersweet nightshade is also nonnative, it established in a shrub bog sometime after wildfire (see Fire adaptations and plant response to fire) [87]. In the central United States, natural revegetation occurred on previously cultivated land in a series of prairie pothole wetlands where the natural hydrological regime had been recently restored. Approximately 3 years after the wetlands were reflooded, bittersweet nightshade occurred on 5 of the 41 sites surveyed [123]. Smith [150] speculated that while bittersweet nightshade may colonize disturbed sites and openings, it may not be a major part of early succession because of its intolerance to drought and the tendency for its branches to die back in winter.

Bittersweet nightshade occurs in forest understories in much of its North American range (see Site Characteristics), including relatively undisturbed forests (e.g., [35,136]) and riparian areas [130], suggesting that it could occur in mid- to late-successional communities. Available evidence suggests, however, that it is more common in earlier stages of forest succession. Bittersweet nightshade is associated with the early-successional scrub stage of beech communities in England that are characteristically open [170]. A study in Norfolk, England found that bittersweet nightshade occurred in open, recently thinned (0-3 years since thinning) deciduous forests and was absent from forests that had not undergone recent thinning (4-33 years since thinning) [5]. In New York, bittersweet nightshade frequency decreased significantly (P<0.025) from 70% to 40% over 60 years in mesic deciduous forests in various successional stages. Although the authors did not speculate as to what caused the decrease in bittersweet nightshade, it did coincide with an increase in canopy cover, particularly of Norway maple [85]. In an urban riparian forest in Manitoba, bittersweet nightshade frequently occurred on shaded sites with approximately 75% canopy cover [121]. Bittersweet nightshade occurred in a remnant oak savanna in Illinois where fire had been excluded for more than 30 years. It was most frequent on sites with low light, and its frequency declined with increased light (see Shade tolerance and Fire management considerations) [12]. A chronosequence study in black cottonwood-dominated stands along the Willamette River in Oregon found that bittersweet nightshade occurred in all successional stages from stand initiation (1 to 5 years) to late seral (45 to >65 years). Bittersweet nightshade was most abundant, however, in the stem exclusion stage (4 to 7 years). In stands where bittersweet nightshade was most abundant, it codominated the riparian plant community, leading researchers to speculate that bittersweet nightshade may threaten successional development in some riparian forests (see Impacts and control) [46]. On sites where bittersweet nightshade is established in the shade, disturbance associated with an increase in irradiance may lower bittersweet nightshade's productivity and inhibit its growth [57,92]. Tolerance of shade-grown bittersweet nightshade to high irradiance may be decreased by even mild water stress [58]. Bittersweet nightshade plants grown in deep shade showed signs of damage on branches when grown at high light intensity in the laboratory [57]. In a greenhouse study, photoinhibition was achieved by transferring bittersweet nightshade plants from shade to 60% sunlight for 2 days. Flushes of nitrogen may offset photoinhibition in bittersweet nightshade; however, if accompanied by water stress, less protection from photoinhibition may be achieved [92].

FIRE EFFECTS AND MANAGEMENT

SPECIES: Solanum dulcamara

FIRE EFFECTS FUELS AND FIRE REGIMES FIRE MANAGEMENT CONSIDERATIONS

FIRE EFFECTS: Immediate fire effect on plant: As of this writing (2009), information pertaining to the immediate effects of fire on bittersweet nightshade is lacking. Bittersweet nightshade is likely top-killed by fire, and its root crown and rhizomes may also be damaged or killed, depending on fire severity and how well they are protected by soil. Chapman and Crow [21] reported that hemicryptophytes as a group generally respond favorably to burning, but species with rhizomes in the litter layer are mostly damaged by fire. It is unclear at what depth bittersweet nightshade rhizomes typically occur in the soil profile.

Postfire regeneration strategy [153]: Rhizomatous shrub, rhizome in soil Caudex or an herbaceous root crown, growing points in soil Initial off-site colonizer (off site, initial community)

Fire adaptations and plant response to fire: As of this writing (2009), little information is available pertaining to bittersweet nightshade's fire adaptations or its postfire response. Bittersweet nightshade's affinity for disturbed sites (see Site characteristics) suggests that it may establish on burned sites after fire. Bittersweet nightshade's seeds do not appear to be long-lived in soils, making on-site colonization by buried seed unlikely (see Seed banking). Postfire establishment is most likely from offsite seed dispersed by birds or mammals. Postfire vegetative regeneration may be possible if rhizomes or roots are not killed or badly damaged [21]. Bittersweet nightshade is known to sprout from its base after being cut or damaged (see Vegetative regeneration) and may do so after fire. However, plants growing in the shade of a forest canopy may not persist following canopy removal (see Successional status).

Although bittersweet nightshade may establish after fire, it may not persist over the long term. In New Zealand, bittersweet nightshade established in a scrub bog following wildfire. Vegetation monitoring during the following 10 years led researchers to classify bittersweet nightshade as a postfire "ephemeral": species that establish on bare ground within 1 year of fire, reach peak cover values for a brief period, then decline or eventually disappear. The authors speculated that bittersweet nightshade established from bird-dispersed seed, possibly obtained from plants growing in disturbed areas or road margins near the bog [87].

FUELS AND FIRE REGIMES:

Fuels Fire regimes

Fuels: As of this writing (2009), information pertaining to bittersweet nightshade's fuel characteristics is limited. In the laboratory, bittersweet nightshade was one of numerous native and nonnative species collected from eastern and mid-Atlantic states that were tested for their combustibility in a cone calorimeter. Based on mean average effective heat of combustion (AEHOC) and mean total heat released (THR), bittersweet nightshade was slightly less combustible than other species tested and did not have any notable combustion characteristics with one exception: peak heat release rate (PHRR) in bittersweet nightshade appeared to increase with the thickness of the material being burned, suggesting that dense patches of bittersweet nightshade might combust more rapidly than small patches or individual plants.

A comparison of combustion properties of select noninvasive and invasive species from eastern and mid-Atlantic states with that of bittersweet nightshade [31] Average effective heat of Mean total heat released (MJ/kg) combustion (MJ/kg) Noninvasive species overall 13.49 12.2 Invasive species overall 13.01 11.72 Bittersweet nightshade 12.29 10.57

The authors speculated that climbing vines like bittersweet nightshade could potentially alter fire behavior by forming ladder fuels [31]. Annual stem growth that dies back each year contributes to the fuel load, and on sites where bittersweet nightshade is abundant or has formed near-monocultures (see Population structure), this contribution may be substantial.

Fire regimes: Bittersweet nightshade's shade tolerance and preference for moist habitats suggest that it may persist in habitats associated with long fire-return intervals. Available literature suggests that in North America, bittersweet nightshade is most common in riparian areas in the eastern, Great Lakes, mid-Atlantic and northwest regions of the United States (see Habitat types and plant communities). Few studies have investigated the behavior, properties, and influence of wildfire in riparian areas. However, riparian forests generally have more available moisture and may differ in understory vegetation, fuel loads, and fuel moisture from adjacent uplands. In these communities, fire typically has longer return intervals and is less severe than in adjacent uplands, especially in the moist forest types [36] where bittersweet nightshade typically occurs.

Bittersweet nightshade is commonly found in moist deciduous forests in the eastern, mid-Atlantic, and Great Lakes regions of the United States. Although stand-replacing disturbances are more often caused by other natural events (e.g., hurricanes, ice storms) than fire in these areas, fire has likely played a role in shaping the structure and composition of the vegetation [185]. Deciduous forests in these regions typically have long fire-return intervals, estimated at several hundred to greater than 1,000 years for mixed-severity or stand-replacement fires and somewhat more frequent for low-severity or surface fires (see the Fire Regime Table).

Although bittersweet nightshade often occurs in vegetation communities associated with relatively long fire-return intervals, it can occur in communities characterized by frequent fire-return intervals, such as oak savanna. Return intervals for stand-replacement fires in oak savannas in the Great Lakes region range from about 50 to 500 years, and return-intervals for surface or low-severity fires range from about 1 to 20 years with an average return interval of 5 years (see the Fire Regime Table).

Bittersweet nightshade occurs in various types of wetlands, most commonly marshes. Fire is important to the maintenance and development of some wetland communities [56,132,173], and fire-return intervals may be relatively short for marshes. Fire regimes for marshes in the Northeast, Southeast, and Northwest may be characterized by high- severity, stand-replacement fires at intervals of 10 years or less (Fire Regime Table).

The Fire Regime Table summarizes characteristics of fire regimes for vegetation communities in which bittersweet nightshade may occur.

Although bittersweet nightshade has not been studied for its potential to alter fire regimes, it is conceivable that bittersweet nightshade could alter fuel characteristics and impact fire regimes especially in riparian areas where it forms near-monocultures.

FIRE MANAGEMENT CONSIDERATIONS: Potential for postfire establishment and spread: As of this writing (2009), bittersweet nightshade had not been studied from a fire management perspective. Fire may hinder its ability to regenerate vegetatively, but its ability to establish on open, disturbed sites (see Successional status) from off-site seed sources suggests that fire could create favorable conditions for bittersweet nightshade establishment. However, frugivorous birds typically prefer woody vegetation for perching [98,150], so for sites where trees and other woody vegetation have been severely damaged by fire, mammals may be the main vector for bittersweet nightshade seed dispersal [96].

Use of prescribed fire as a control agent: Information pertaining to the use of fire as a control for bittersweet nightshade is limited. One study suggested that increased fire frequency might help to control nonnative species on a site where bittersweet nightshade occurred [12]. Thirty years of fire exclusion in a remnant oak savanna in Illinois had altered community structure from an open-canopy savanna with few canopy trees, toward a closed-canopy forest with few gaps. Bittersweet nightshade occurred in the savanna, primarily under canopy trees (see Successional status), and was one of a few dominant nonnative species on this site. Based on the negative relationship observed between increases in light and nonnative species richness, the authors suggested that restoring light levels to the site by increasing fire frequency may reduce nonnative species richness on this site. The authors cautioned, however, that prescribed fire alone may not permanently reduce nonnative species because some may sprout after fire or respond favorably to increased light; subsequent herbicide applications may be necessary (see Impacts and control). The authors also indicated that more information on the ground-layer vegetation and its response to light gradients was needed before prescribed fire could be considered as a management option in the savanna [12].

Another study from east-central Minnesota used prescribed fire over a 20-year period in an attempt to restore oak savanna on a site that had transitioned to oak forest as a result of fire exclusion [160]. Fire was reintroduced to 9 sites at varying return intervals ranging from about once a year to once every 10 years. Bittersweet nightshade was one of 113 plant species that occurred in the study area 20 years after prescribed fire was introduced, suggesting fire may not prevent its occurrence. However, information pertaining to its prefire occurrence and its postfire abundance is lacking, making it difficult to determine its relationship to fire. Additionally, it is unclear if bittersweet nightshade occurred on sites burned frequently, on sites burned every 10 years, or in unburned sites used as a control [160], making it difficult to infer how fire-return interval might influence its populations.

Fire suppression and disturbance: Fire prevention and suppression techniques often disturb soil and vegetation on unburned sites and could provide opportunity for bittersweet nightshade establishment. In California, a small amount of bittersweet nightshade established in one plot (n>1000) on areas cleared for a fuel break [118].

For general recommendations on preventing establishment and spread of invasive plants during fire suppression activities or after wild or prescribed fire, see the following publications: [6,15,62,162].

MANAGEMENT CONSIDERATIONS

SPECIES: Solanum dulcamara

IMPORTANCE TO WILDLIFE AND LIVESTOCK OTHER USES IMPACTS AND CONTROL

IMPORTANCE TO WILDLIFE AND LIVESTOCK: Although bittersweet nightshade is nonnative in North America, reviews indicate that it has food and cover value for wildlife [53,111,182,183], but it has not been reported as a major food source for any species with the exception of bumblebees. In Ontario, Canada, larval colonies of 2 species of bumblebees contained 64% to 71% bittersweet nightshade pollen [108].

Birds typically digest the fleshy portion of bittersweet nightshade's fruit and expel the seed (see Seed dispersal). Birds adapted to foraging in vegetation, which can reach fruit while perched on a branch and are not restrained by a small gape, are more likely to eat bittersweet nightshade fruit than birds lacking these characteristics [9]. Frugivorous birds such as crows [75], eastern kingbirds [106], mimic-thrushes, thrushes, white-crowned sparrow, and waxwings [8,154] eat the fruits of bittersweet nightshade. Numerous other songbirds and upland gamebirds throughout the United States also eat bittersweet nightshade fruit, especially in the Northeast and Southwest (review by [111]). Ring-necked pheasants eat the fruit of bittersweet nightshade [29,95], especially as an emergency food source during ice storms [29]. In the United Kingdom, bittersweet nightshade fruit is the primary food for blackcaps ([9], review by [151]) and is also used by blackbirds, song thrush, robin, starling, and spotted flycatcher. Bullfinches are the only known bird that regularly eats bittersweet nightshade fruit for its seed rather than its flesh (review by [151]).

Mammals that occasionally eat bittersweet nightshade fruit include black bear in Oregon [19], Virginia opossum in New York [70], eastern cottontail rabbits in Massachusetts [156], and white-tailed deer in the eastern United States [124]. A review indicated that common muskrats graze on the stems of bittersweet nightshade [53]. Herbivory by invertebrates on bittersweet nightshade has been reported in North America [168].

Palatability/nutritional value: The fruit of bittersweet nightshade is about 85% water [42,151,176] and may have low to moderate nutritional value. Herrera [76] calculated the relative yield (i.e., the dry, nutritive matter as a percent of total fruit mass) from available literature, for fruits of 15 tropical and 69 temperate bird-dispersed plants. Based on these calculations, the fruit of bittersweet nightshade had greater nutritional value than that of many plants with tropical origins, but less than that of many species of nontropical origins. A review by Snow and Snow [151] reported that the relative yield (i.e., the dry, nutritive matter as a percent of total fruit mass) for bittersweet nightshade fruit is low (12.5%) because the pulp is watery. When compared to fruits of other temperate region plants, bittersweet nightshade fruits contained near average percent nitrogen (1.15%) and carbohydrates (29.60%) but below average percent fat (1.00%) [8]. Together, the fruit and seed of bittersweet nightshade had a relatively high crude fat content (28%) [154], while the fruit pulp alone was low in lipids and calorie content [176]. An analysis of fruiting plants introduced to New Jersey found that the dry pulp of bittersweet nightshade fruit provided greater energy (18.63 kj/g) and contained more protein (6.2%) than that of most other introduced plants tested, but was low in fat ( 0.5% lipid) [176].

Bittersweet nightshade contains solanine (glycoalkaloid and alkamines collectively), a mildly toxic substance known to be poisonous ([42,81,88,159,178], review by [55]) to humans, livestock, mice, dogs and rabbits ([48,81], reviews by [53,55,104]). Unripe berries have the highest concentration of toxins, followed by vegetative tissue, and then ripe berries [55]. While some describe the amount of toxin in bittersweet nightshade as not "dangerously poisonous" (review by [59]), others report that children may be especially sensitive to it (review by [164]). A handbook on poisonous plants indicated that bittersweet nightshade is only likely to cause symptoms in humans who have eaten 10 or more unripe berries; a fatal dose would require about 200 unripe berries [55]. In large doses, solanine will slow the heart, reduce body temperature, cause vertigo, delirium, convulsions and possibly death (review by [104]). If ingested by horses, bittersweet nightshade can cause labored breathing, nausea, weakness, trembling, constipation, diarrhea, and possibly death [48]. Laboratory mice that ingested bittersweet nightshade fruit of various degrees of ripeness experienced gastrointestinal problems or behavioral changes [81].

Ripe bittersweet nightshade berries are also poisonous, which may reduce their palatability for some wildlife [8]. Evidence indicates that bittersweet nightshade is not toxic to birds ([8,9], reviews by [59,151]) but may be toxic to some mammals, which likely makes the fruit unpalatable. In a controlled experiment, bittersweet nightshade was found to be highly palatable to cedar waxwings, moderately palatable to American robins and white-crowned sparrows, and not palatable to yellow-pine chipmunks. A taste test determined that bittersweet nightshade fruit was not palatable to humans [8].

Cover value: While not preferred, bittersweet nightshade is occasionally used for nesting. Gray catbirds in the central portions of North America and Ontario, Canada, occasionally (< 1% of their nests) built nests in bittersweet nightshade [127]. American eiders nesting along Maine's Penobscot Bay occasionally used bittersweet nightshade; however, nesting success (i.e., percent hatched) was lower in nests constructed in bittersweet nightshade than in nests constructed in most native vegetation [22].

OTHER USES: Bittersweet nightshade has been studied primarily for its secondary chemicals (review by [14]) and used for its medicinal properties. Bittersweet nightshade contains small amounts of compounds that have been studied for their potential medicinal importance [80,82]. In North America bittersweet nightshade was widely prescribed for its narcotic, diuretic, alterative, and cleansing principles during the latter half of the nineteenth century. It was thought to relieve many ailments including leprosy, skin diseases, cutaneous diseases, rheumatic infections, ulcers, sores, and gland swelling. Although bittersweet nightshade is not widely used today, extracts from its roots, bark, and shoots are still prescribed for their narcotic principles in rheumatism, circulation, ulcers, and skin afflictions (reviews by [53,104]).

Bittersweet nightshade has been cultivated for ornamental purposes (reviews by [182,183]), and seeds are still available for purchase from online distributors. However, a review on seeds suggests that any ornamental values of bittersweet nightshade are offset by its poisonous properties [66].

IMPACTS AND CONTROL: Impacts: A review indicated that bittersweet nightshade was typically not abundant or aggressive enough to require control [53]. The Nature Conservancy has given bittersweet nightshade a national ranking of "low" based on its overall low ecological impacts, but they are moderately concerned about its widespread distribution and abundance [126].

Bittersweet nightshade likely poses the greatest threat in portions of North America where it is most common (see General distribution), especially in riparian communities where it is most likely to be abundant (see Population structure and Site characteristics) ([46], reviews by [93,125,126]). On sites where it is abundant, bittersweet nightshade's ability to grow over trees and shrubs may cause changes in community structure (reviews by [93,117,126]) and, to a lesser extent, composition (review by [126]). In Oregon, Fierke and others [46] suggested that dense homogenous patches of bittersweet nightshade may inhibit germination and establishment of native plants. They further speculated that invasive species such as bittersweet nightshade may be a threat to successional development in cottonwood riparian forests.

In Oregon, bittersweet nightshade is ranked as "moderately invasive" in wetlands and riparian areas. Weeds with this ranking moderately impact native habitats but likely do not cause native plant or invertebrate extirpations [125]. An analysis of invasive plant survey data from the upper Great Lakes states ranked invasive species on their ability to invade natural plant communities. Bittersweet nightshade was given a 3.3 ranking on a scale of 0 to 10 (0 = little or no ecological impact, 10 = invades and replaces native plant communities) [136]. Field records from New England indicate that bittersweet nightshade typically occurs as a single plant or in small patches (1 to 20 plants) that comprise 5% or less of the overall vegetation cover. Larger populations (20-99 plants) of bittersweet nightshade occasionally occur, and on one site bittersweet nightshade cover was greater than 25% [117].

Bittersweet nightshade occurs in non-riparian sites; however, information pertaining to its invasiveness in these communities is limited. Although it occurs in non-riparian deciduous forest communities in eastern North America, available literature suggests that its abundance may decline or remain steady over time [79,85]. In the Great Lakes region, bittersweet nightshade is considered a "lesser invader" of forests and wetlands (review by [28]). Smith [150] speculated that bittersweet nightshade may not persist on dry sites over time, suggesting that its impacts in non-riparian areas may not be long-lasting (see Successional status).

Information pertaining to bittersweet nightshade's invasiveness in portions of North America where it is less common is limited and may indicate that its impacts are less severe in these areas. In Utah and the Great Plains, bittersweet nightshade is "rarely encountered" [64,174], in Colorado it was collected in only 1 drainage [172], and in North Carolina, bittersweet nightshade is rare and typically occurs in the mountains [134]. Although some of these reports are dated, a national invasive species database [126] indicates that bittersweet nightshade has not become more of a threat in these areas in recent times. Its ability to grow in warm climates suggests that it may continue to spread to other areas in the south (e.g. into Arkansas) (review by [126]).

In the Netherlands, bittersweet nightshade may be an alternative host for late blight (Phytophthora infestans), a pathogen that negatively impacts agricultural crops in the Solanaceae family. Infection in bittersweet nightshade, however, appears to be uncommon [49].

Control: Control of invasive plant species is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders [110]. Numerous methods have been suggested to control the spread of bittersweet nightshade, but information pertaining to their effectiveness in wildlands is limited. Regardless of the control method employed, removal of moderate to large infestations of bittersweet nightshade should be followed by replanting with desirable species to minimize reinvasion by bittersweet nightshade or other weeds. All treatments should be followed by monitoring for several years to help identify further infestations and determine survival of planted material (review by [93]).

Prevention: Early detection followed by immediate eradication helps to prevent the spread of many invasive plant species. Small infestations of bittersweet nightshade are easy to identify from mid-May to late fall, when it is flowering or fruiting. Manual control of new infestations and subsequent site monitoring may help prevent initial infestations from spreading (review by [93]).

Occasionally, bittersweet nightshade is still cultivated (review by [126]). Discouraging its commercial distribution and deliberate planting may help to prevent accidental introduction into native habitats.

Integrated management: Integrated management focuses not only on eradicating the target plant but also on establishing desirable species and maintaining weed-free systems over the long term. The King County Noxious Weed Control Program in Washington (review by [93]) recommends integrated management to maximize control of bittersweet nightshade and minimize negative impacts to the site. For large infestations, bittersweet nightshade can be cut with loppers or brushed mowed, followed by digging up roots or spot-spraying any remaining growth with an appropriate herbicide. As an alternative to herbicide, remaining growth can be covered with a heavy duty fabric to suppress further growth (review by [93]).

Physical or mechanical control: Bittersweet nightshade may be controlled manually by pulling or digging up the roots, which is easier when the ground is wet or loose (reviews by [28,53,59,93]). This method is most effective with young plants or new infestations (review by [93]). Care must be taken not to break the rhizomes or roots because fragments may regenerate vegetatively ([58,89], reviews by [93,183]).

Other physical or mechanical methods of control include repeat cutting or covering plants with a weed barrier (review by [93]). In a field in New York, however, repeat mowing failed to eliminate woody plant species including bittersweet nightshade [167].

Fire: See Fire Management Considerations.

Biological control: There are currently no biological control agents available for bittersweet nightshade (review by [93]).

Chemical control: Bittersweet nightshade may be controlled with selective broadleaf or broad-spectrum herbicides (reviews by [53,93]) but to what extent is uncertain. Following herbicide treatment, bittersweet nightshade should not be cut back until foliage turns brown or is dead (review by [93]). Several applications in the same year or consecutive years may be necessary for adequate control ([40], review by [93]). A few publications provide information on potential chemical treatments ([38,39,40], review by [93]). See The Nature Conservancy's Weed Control Method Handbook [161] for information on specific chemicals and how to correctly use herbicide in wildlands. Only herbicides approved for use in and near water can be used to control bittersweet nightshade infestations in riparian areas and other habitats adjacent to water. To prevent damage to desirable species, herbicide application should be done before other plants emerge or after they have gone dormant (review by [93]). For most weeds, herbicides are effective in gaining initial control of a new invasion or a severe infestation, but they are rarely a complete or long-term solution to weed management [20].

A 1919 review suggests that pouring hot brine or caustic soda around the roots will control bittersweet nightshade [59].

Cultural control: No information is available on this topic.

APPENDIX: FIRE REGIME TABLE

SPECIES: Solanum dulcamara

Fire regime information for vegetation communities in which bittersweet nightshade may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [103]], 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. Pacific Northwest Great Lakes Northern and Central Rockies Northern Great Plains Northeast Southern Appalachians Southeast South-central US Southwest Pacific Northwest

Replacement 74% 7 Marsh Mixed 26% 20 Southwest

Fire regime characteristics Vegetation Community (Potential Fire Natural Vegetation Group) severity* Mean Minimum Maximum Percent interval interval interval of fires (years) (years) (years) Southwest Forested Riparian forest with conifers Replacement 100% 435 300 550 Replacement 50% 110 15 200 Riparian deciduous woodland Mixed 20% 275 25 Surface or 30% 180 10 low Northern and Central Rockies

Riparian (Wyoming) Mixed 100% 100 25 500 Northern Great Plains

Northern Plains Grassland Northern Plains Woodland

Replacement 7% 44

Oak savanna Mixed 17% 18 Surface or 76% 4 low Northern Plains Woodland

Replacement 38% 45 30 100 Northern Great Plains wooded draws and ravines Mixed 18% 94 Surface or 43% 40 10 low

Great Plains floodplain Replacement 100% 500

Great Lakes Great Lakes Woodland Great Lakes Forested

Replacement 4% 110 50 500

Northern oak savanna Mixed 9% 50 15 150 Surface or 87% 5 1 20 low Great Lakes Forested

Northern hardwood maple-beech- Replacement 60% >1,000 eastern hemlock Mixed 40% >1,000 Mixed 7% 833 Great Lakes floodplain forest Surface or 93% 61 low

Replacement 33% >1,000 Maple-basswood Surface or 67% 500 low

Maple-basswood mesic hardwood forest Replacement 100% >1,000 >1,000 >1,000 (Great Lakes)

Replacement 4% 769

Maple-basswood-oak-aspen Mixed 7% 476 Surface or 89% 35 low

Northern hardwood-eastern hemlock Replacement 99% >1,000 forest (Great Lakes)

Replacement 13% 66 1

Oak-hickory Mixed 11% 77 5 Surface or 76% 11 2 25 low Northeast

Northeast Grassland Northeast Forested

Replacement 97% 7 2 50 Northern coastal marsh Mixed 3% 265 20 Northeast Forested

Replacement 39% >1,000 Northern hardwoods (Northeast) Mixed 61% 650

Replacement 72% 475 Eastern white pine-northern hardwoods Surface or 28% >1,000 low

Replacement 50% >1,000 Northern hardwoods-eastern hemlock Surface or 50% >1,000 low

Northern hardwoods-spruce Replacement 100% >1,000 400 >1,000

Replacement 2% 625 500 >1,000

Appalachian oak forest (dry-mesic) Mixed 6% 250 200 500 Surface or 92% 15 7 26 low Beech-maple Replacement 100% >1,000

South-central US

Replacement 7% 250 50 300 Interior Highlands dry-mesic forest and woodland Mixed 18% 90 20 150 Surface or 75% 22 5 35 low

Replacement 42% 140 Southern floodplain Surface or 58% 100 low

Replacement 42% >1,000 Southern floodplain (rare fire) Surface or 58% 714 low Southern Appalachians

Southern Appalachians Woodland Southern Appalachians Forested

Replacement 23% 119

Oak-ash woodland Mixed 28% 95 Surface or 49% 55 low Southern Appalachians Forested

Replacement 25% 435 200 >1,000

Bottomland hardwood forest Mixed 24% 455 150 500 Surface or 51% 210 50 250 low

Replacement 11% 665

Mixed mesophytic hardwood Mixed 10% 715 Surface or 79% 90 low

Replacement 3% 180 30 500

Appalachian oak-hickory-pine Mixed 8% 65 15 150 Surface or 89% 6 3 10 low

Replacement 17% >1,000 500 >1,000 Eastern hemlock-eastern white pine- hardwood Surface or 83% 210 100 >1,000 low

Replacement 6% 220

Appalachian oak forest (dry-mesic) Mixed 15% 90 Surface or 79% 17 low

Southern Appalachian high-elevation Replacement 59% 525 forest Mixed 41% 770 Southeast

Southeast Grassland Southeast Forested

Floodplain marsh Replacement 100% 4 3 30

Southern tidal brackish to freshwater Replacement 100% 5 marsh

Southeast Forested

Replacement 7% 900 Southern floodplain Surface or 93% 63 low *Fire Severities— 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 [72],102]].

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