Botanical description: This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [11,25,44,56,57,60,105,122,148,173]).
Aboveground description: White mulberry grows as a dense, round-topped, perennial shrub or tree (review by [33]), reaching heights around 50 feet (15 m) [44]. The thin bark is shallowly furrowed and has long, narrow ridges [44]. White mulberry leaves are alternate, simple, ovate, 2 to 4 inches (6-10 cm) long and 1 to 2 inches (3-6 cm) wide, with margins varying from coarsely serrate to deeply lobed and serrate. Leaves exude a milky juice when broken. Staminate and pistillate flowers develop in separate catkins [143]. Plants are typically dioecious [18,48] and occasionally monoecious [21]. White mulberry fruits are cylindrical drupes, 0.5 to 1.0 inches (1.5-2.5 cm) long. Fruits may be black, purple, or white. The ovoid nutlet has a thin, soft shell [143], and the seed has a "hard bony coat" [85].
White mulberry fruit.Belowground description: White mulberry has a wide, spreading root system ([41,138,143], review by [30]), with both a tap root and lateral roots [138]. Roots are large in diameter close to the root crown but decrease rapidly in size, branching within a few feet of the root crown into numerous fibrous roots [17]. Roots of a 21-year-old white mulberry penetrated approximately 7 feet (2 m) deep and had a 22-foot (7 m) lateral spread in silty clay loam soil in eastern Nebraska [138]. In Oklahoma, 5 planted white mulberry trees penetrated to a depth of 13 feet (4 m) in a deep silt loam. The longest lateral root extension was 42 feet (13 m). Most lateral roots occurred in the upper 1 to 3 feet (0.3-1 m) of soil, and no lateral roots occurred below 5 feet (2 m); average lateral root spread was calculated at 190 to 330 ft² [17].
Life span: White mulberry trees may have a long life span; at Mt. Vernon, a white mulberry planted by George Washington in 1785 was alive as of 1990 (review by [106]). There are records of 150-year-old white mulberry trees in Greece (review by [86]) and a 120-year-old planted white mulberry tree in Utah (review by [106]).
White mulberry is native to China [23,110,168] and was introduced to North America in the 1600s (reviews by [18,33]). In 1624 the legislature of Virginia required every male resident to plant at least 4 white mulberry trees to promote a North American silk industry. By the 1830s, the potential for a silk industry prompted a horticultural phenomenon known as "mulberry mania" in the eastern United States. In the late 1830s, white mulberry plantations in the Northeast were killed by cold winters and those in the South were killed by disease, halting the planting of white mulberry. However, white mulberry seeds were imported from Europe in the 1860s to promote a silk industry in Utah (review by [106]).
White mulberry has established outside of cultivation in many areas [11,25,56,57,96,105,110,122,148,168,173,179,180]. As of this writing (2009), white mulberry is widely distributed across North America, occurring across all of the United States with the exceptions of Nevada and Alaska. In Canada, it is found in British Columbia, Ontario, and Quebec. Plants Database provides a distribution map of white mulberry.
Preventing postfire establishment and spread: While there is little documented information regarding the postfire establishment and spread of white mulberry (2009), the potential for vegetative regeneration from stumps [150] and roots (reviews by [21,136]), and the documentation of white mulberry sprouting 3 years following wildfire in New Mexico [161], suggest that managers should monitor top-killed white mulberry plants for any signs of regeneration. White mulberry seeds may survive in the soil seed bank or be dispersed from off-site sources, though it is not clear whether postfire conditions are conducive to white mulberry seed germination and seedling establishment (see Fire adaptations).
Preventing invasive plants from establishing in weed-free burned areas is the most effective and least costly management method. This may 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: [4,14,58,162].
Use of prescribed fire as a control agent: As of this writing (2009) there were no studies documenting the use of prescribed fire to control white mulberry. Control may be limited by the potential of white mulberry to sprout from the stump [150] or roots (reviews by [21,136]). One review suggests that white mulberry roots will continue to produce sprouts even if the plant is cut back every year [21], suggesting that repeated fires or integrated treatments may be needed to control mature white mulberry.
Fuels: As of 2009, no studies specifically addressed fuel characteristics of white mulberry. An ornamental white mulberry in Bakersfield, California, had a projected leaf mass per area of crown of 990 g/m² [77].
Where white mulberry occurs within the range of red mulberry and exhibits growth patterns similar to those of red mulberry, it is unlikely that local fuel characteristics would be altered. Fuel characteristics could potentially be altered in areas where white mulberry establishes in densities and/or growth patterns differing from those of native vegetation, such as where it develops in dense thickets (e.g., see [120]). It is also possible that white mulberry alters fuel characteristics in areas where post-settlement fire exclusion facilitated the establishment of woody species like white mulberry, as was documented in riparian forests in south-central Nebraska [130] and upland areas adjacent to hardwood gallery forests in the northern Great Plains [81].
FIRE REGIMES: It is not known what type of fire regime white mulberry is best adapted to. The current North American distribution of white mulberry includes ecosystems that historically experienced both frequent and infrequent fires of various severities. The impact of white mulberry on these FIRE REGIMES is largely unknown. One study suggests that fire exclusion in hardwood gallery forests in the northern Great Plains has facilitated spread of plants like white mulberry out of riparian corridors and into adjacent upland areas with historically high fire frequencies [81].
See the Fire Regime Table for further information on FIRE REGIMES of vegetation communities in which white mulberry may occur. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Greenhouse experiments show variable germination rates, with germination generally improving with cold stratification ([85], review by [33]), and variable results after ingestion by wildlife [12,85]. Wild-collected white mulberry seeds showed high germination rates (92.3%) in greenhouse trials where seeds were exposed to indirect sunlight and fluctuating temperatures from June to October. Germination rates were lower (78.3%) for seeds that had been ingested by box turtles prior to germination trials [12]. Another study found that dormancy of white mulberry seeds varies; seeds from the same cohort may exhibit seed coat dormancy, embryonic dormancy, or both. Seeds exhibiting all 3 types of dormancy showed improved germination following both cold stratification and digestion by American robins. Seeds had germination rates of 45.8% when just digested by American robins and 68.8% when digestion by American robins was combined with 90-day cold stratification. In contrast, control seeds with no treatment had a germination rate of 34.0% while those only exposed to cold stratification had a germination rate of 55.2%. Scarification of control seeds with a 15-minute sulfuric acid treatment reduced germination rates [85].
A forestry handbook from India reports that white mulberry seeds take 35 days to germinate [111], though one review reports an expected germination rate of 73% to 84% 8 to 12 days following 60-day stratification in sand [141].
General site types: White mulberry establishes in a variety of site types, including largely native plant communities, as well as many sites associated with human disturbance. It commonly establishes in the understory of floodplain [3,35,47,52,60,65,72,82,98,142,144,152,170,178] or riparian [26,36,53,73,79,91,92,94,99,126,130,145,164,167,178] plant communities. Floras report white mulberry occurring in wooded areas [60], "woods" [168], forest or woodland edges ([41,44,153]), dry to moist thickets [44], low stream banks, drained woods [147], or prairie hills [143].
White mulberry establishes in disturbed [44,179,180], ruderal [25,28], and "waste" areas ([41,96,177], review by [30]), including areas along roadsides ([53,60,96,153,156], review by [30]), railroad tracks [108,168], levees [156], and near dwellings [122], and in vacant lots [168], pastures ([122,158], review by [30]), fields [45,153,168], fencerows ([28,41,44,60], review by [30]), hedgerows [144,168], or windbreaks [122].
Climate: Given the wide geographic range of white mulberry, climate does not seem to particularly restrict its establishment. White mulberry occurs in areas with subtropical humid climates like southeastern Alabama, with long hot summers and short, mild winters [132]. It also occurs in the semiarid and continental climate of eastern Colorado, with high daily and annual temperature ranges, high potential evapotranspiration rates, and strong winds [79]. White mulberry tolerates the cold temperatures of Massachusetts, where average January temperatures are 23 °F (-5 °C) and average July temperatures are 68 °F (20 °C) [7], as well as the warm temperatures of locations like northern Alabama where average January temperatures are 45.5 °F (7.5 °C) and average July temperatures are 80.1 °F (26.7 °C) [10]. However, reports from northwestern Oklahoma indicate the tips of branches are susceptible to freezing [64], and cold winters in the Northeast killed white mulberry plantations in the 1830s (review by [106]).
White mulberry tolerates a wide range of annual precipitation, occurring in areas where reported average annual precipitation ranges from 11 inches (286 mm) in central Arizona [178] to 60 inches (1,400 mm) in northern Alabama [10].
Reported average annual precipitation for locations where white mulberry occurs in the United States Location Average annual precipitation (mm)* Northern Alabama 1,270-1,400 [10] Central Arizona 286 [178] Eastern Colorado 470 [79]** Southwestern Indiana 1,140 [117] South-central Kansas 760 [119] Southeastern Kentucky 1,170 [133] Massachusetts 1,190 [7]** Southwestern Michigan 860 [45] West-central Ohio 945 [76] Northeastern Oklahoma 1,045 [54] West-central Oklahoma 760 [93] Southeastern Washington 330 [92]*Values are for annual precipitation unless otherwise noted
**Annual rainfall
Elevation: In North America, white mulberry occurs from 0 to 5,000 feet (0-1,500 m) [44]. It does not appear to be restricted to particular elevations and may occur at high elevations outside North America.
Reported elevation of sites with white mulberry Location Elevation (feet) Central Arizona 2,000 [178] Grand Canyon area of northern Arizona 3,100 [145] Southwestern Indiana 434 [117] Southeastern Kentucky 801-1,610 [133] Massachusetts 300-1,000 [7] Central Missouri 540 [35] North-central Tennessee 350-380 [75] Northern Pakistan 8,500 [116]Soil: White mulberry occurs on a variety of soil types. One review states that white mulberry prefers rich loamy soil [141]. It establishes on silt loam in southwestern Indiana [117], central Ohio [36], and northwestern Tennessee [22], clay loam in central Missouri [35], and sandy loam in southwestern Michigan [45] and central New Jersey [47]. In northwestern Oklahoma white mulberry tolerates both sandy and loamy soil textures [64]. It is associated with sandy soil in Kansas [82,119], northeastern Oklahoma [54], coastal Louisiana [39], and southeastern New York [90].
A manual to woody landscaping plants reports that white mulberry grows best in fertile soils [33], though one review states that it tolerates poor soils [30]. White mulberry occurred on nutrient-rich soils in southeastern New York [90].
White mulberry is adapted to a range of soil pH (review by [33]). It was found on neutral soils in both northern Alabama [10] and southeastern New York, but was not found on acidic soils in southeastern New York [90]. In north-central Texas, white mulberry established in limestone areas [32].
A manual to woody landscaping plants states that white mulberry grows best in moist, well-drained soils [33], though it has established in both well-drained ([16,36,39], review by [141]) and poorly drained soils [39].
Impacts:
Native vegetation: There is widespread concern over white mulberry's hybridization with the native red mulberry ([18,153,171,174], review by [30]). In Ontario, resulting hybrids were more similar to white mulberry parents, suggesting the potential for a local extinction of red mulberry [18]. In 1963, white mulberry was more common than red mulberry in southeastern Kansas [55]. There is also some concern in the mid-Atlantic region that white mulberry may transmit a harmful root disease to red mulberry [153].
Though it generally grows at relatively low densities, white mulberry has the potential to exclude native vegetation (review by [51]), particularly where it grows in dense thickets. However, as of this writing (2009) there was little published information documenting this impact. On a dredge spoil island in South Carolina, 95% of a 22.5 acre (9.1 ha) area was covered by a closed-canopy, even-aged stand of white mulberry. No understory was present [120]. White mulberry also established in thickets in limestone areas in north-central Texas [32], though no impact on native vegetation was reported.
White mulberry infestation.White mulberry may have allelopathic properties; in laboratory experiments, white mulberry leaf leachate inhibited the germination of India mustard (Brassica juncea) [2].
Other impacts: Spreading white mulberry roots damaged pavement and curbs in San Francisco (review by [33]).
Control: In all cases where invasive species are targeted for control, no matter what method is employed, the potential for other invasive species to fill their void must be considered [14]. Control of biotic invasions is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders [95].
As of this writing (2009), very little information was available regarding control of white mulberry. The potential of white mulberry to sprout from the stump [150], roots (reviews by [21,136]), or from cut stems buried in the soil (review by [30]) may complicate control efforts. Information presented in the following sections may not be comprehensive and is not intended to be prescriptive in nature. It is intended to help managers understand the ecology and control of white mulberry in the context of fire management. For more detailed information on control of white mulberry, consult the references cited here or local extension services.
Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.
Prevention: Because white mulberry is often planted as an ornamental, one way to prevent future white mulberry establishment is to avoid planting it. In the mid-Atlantic region, native alternatives to white mulberry include red maple, hackberry, black tupelo, or sassafras [153].
It is commonly argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" natural communities [95,135] (e.g., avoid road building in wildlands [160]) and by monitoring several times each year [74]. Managing to maintain the integrity of the native plant community and mitigate the factors enhancing ecosystem invasibility is likely to be more effective than managing solely to control the invader [67].
Weed prevention and control can be incorporated into many types of management plans, including those for logging and site preparation, grazing allotments, recreation management, research projects, road building and maintenance, and fire management [162]. See the Guide to noxious weed prevention practices [162] for specific guidelines in preventing the spread of weed seeds and propagules under different management conditions.
Cultural control: No information is available on this topic (2009).
Physical or mechanical control: White mulberry seedlings may be controlled by pulling. For larger white mulberry plants, stems may be cut and the stump ground [153]. Girdling is also an option for larger trees ([153], review by [30]). Mechanical control may be limited by the potential of white mulberry to sprout from the stump [150], roots (reviews by [21,136]), or from cut stems buried in the soil (review by [30]). One review suggests that roots will continue to produce sprouts even if the plant is cut back every year [21].
Biological control: Biological control of invasive species has a long history that indicates many factors must be considered before using biological controls. Refer to these sources: [165,176] and the Weed control methods handbook [159] for background information and important considerations for developing and implementing biological control programs.
As of this writing (2009) there were no biological control programs identified for the control of white mulberry. White mulberry is susceptible to several diseases in North America (review by [137]). In the southern United States, white mulberry may be susceptible to popcorn disease caused by the fungus Ciboria carunculoides [59].
Goat browsing was used to suppress white mulberry in prairie remnants in northwest Illinois [8].
Chemical control: 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 [19]. See the Weed control methods handbook [159] for considerations on the use of herbicides in natural areas and detailed information on specific chemicals.
No detailed information was found describing the use of herbicides to control white mulberry (as of 2009), though 1 review states that herbicides may effectively control white mulberry [30]. One handbook on invasive species in the mid-Atlantic region suggests controlling white mulberry by cutting stems and painting the stump with glyphosate [153].
Integrated management: No information is available on this topic (2009).
Palatability and/or nutritional value: Both the foliage and fruit of white mulberry are edible to livestock and wildlife. White mulberry foliage contains high levels of protein, carbohydrates, fats, fibers, vitamins and minerals (review by [20]), though a high tannin content may limit its digestibility [5]. White mulberry foliage from Pakistan contained crude protein ranging from 13.7% to 17.6% of dry mass [5]. White mulberry foliage was eaten by domestic sheep and goats in Greece (review by [86]) and was browsed by reintroduced elk in southeastern Kentucky [133]. Consumption of white mulberry foliage by silkworms is the foundation of the international silk industry ([44,168], review by [20]). Grasshoppers defoliated white mulberry foliage in Utah (review by [106]).
White mulberry fruits from India were high in Vitamin C, and dry samples contained 5.5% protein and 87.55% carbohydrates [149]. White mulberry fruits are eaten by birds ([23,71,113,121,173], review by [30]), red foxes [83], northern raccoons, Virginia opossums, squirrels [71], and other mammals (review by [30]).
Cover value: White mulberry provides general cover, as well as foraging and nesting habitat, for many bird species. White mulberry is recommended as a shelterbelt tree to improve general wildlife habitat in the Great Plains [66] and to provide vegetative cover for bobwhite quail in northwestern Oklahoma [64]. In a floodplain woodland in southeastern Washington, white mulberry provided important summer foraging habitat for both summer- and permanent-resident birds; birds were observed gleaning insects off of living white mulberry branches and leaves [92].
Shelterbelt white mulberry provided nesting habitat for Mississippi kites in northwestern Oklahoma [94]. Wood thrushes nested in white mulberry in southeastern Pennsylvania [68]. Great blue herons, white ibises, glossy ibises, great egrets, black-crowned night herons, tricolored herons, and yellow-crowned night herons nested in a dense stand of white mulberry on a dredge spoil island in South Carolina [120]. On a coastal island in North Carolina, white mulberry was preferred by nesting great egrets, and also provided nesting habitat for snowy egrets, cattle egrets, little blue herons, and Louisiana herons [101].
Silk production: White mulberry leaves provide the natural food for silkworms. Consequently, white mulberry has been widely planted throughout the world to develop the silk industry ([44,168,173], review by [106]).
Food value: White mulberry fruits are edible to humans ([32,116], reviews by [20,30]), though unripened fruit can cause stomach irritation, nervous system stimulation, and hallucinations (review by [30]). Dried white mulberry fruits may be ground up as flour and young shoots may be cooked as a vegetable [38]. White mulberry powder has been used as a preservative for wheat flour (review by [20]).
Medicinal value: White mulberry is used for a variety of medicinal purposes. The juice of white mulberry berries is used in the treatment of jaundice and hepatitis in rural areas in Pakistan [1]. It is valued for its antimicrobial properties, antioxidant potential, and in the prevention or treatment of diseases such as diabetes, atherosclerosis, immunonutrition, cancer, neurodegenerative disorders including Alzheimer's disease, and skin disorders (review by [20]). Native Americans used infusions made from white mulberry bark as a laxative, a treatment for dysentery, and a purgative [44].
Other value: White mulberry is widely planted as an ornamental shade tree [44,60] or is used in shelterbelts [60,122,143,168]. It has been evaluated for its potential to phytoremediate seleniferous soils in India [31]. White mulberry exhibited low survival and growth after planting on acidic surface-mine soils in Kentucky [118,157]. The leaves of white mulberry are used to make a yellow dye in Turkey [34].
The milky sap of white mulberry is toxic to humans and irritates the skin (review by [30]).
White mulberry reproduces by seed. Following injury, white mulberry may regenerate vegetatively via sprouting from the stump, roots, or cut stems, though this response is not widely documented.
A forestry handbook from India lists white mulberry seeds as viable for 720 days [111]. Tests at a nursery in Nebraska found that, while white mulberry seeds remained viable for at least a year when stored in cool, sealed conditions, they deteriorated rapidly upon removal from storage [154].
White mulberry seeds have been found in soil samples even when mature plants are not present in extant vegetation, though the seeds were not always viable. White mulberry was absent from aboveground vegetation but present at low density in the soil seed bank in deciduous forests in Bronx, New York, with viable seeds occurring at a soil depth of 0 to 4 inches (0-10 cm) [84]. White mulberry seeds were detected in 32% of soil samples taken from a woodlot in southern Ontario in November, occurring in samples at a density of 334.8 seeds/m². These seeds were not viable in seedling emergence trials [15]. In west-central Iowa, white mulberry seeds were present in the seed bank in coniferous woodland, deciduous shrub, tallgrass prairie, and midgrass prairie plant communities. Neither the viability of these seeds nor white mulberry's presence in the aboveground vegetation were reported [127]. In southeastern Arizona, white mulberry was found in the soil seed bank of a riparian deciduous forest but was not found in extant vegetation [125].
As of 2009, there was little published information regarding conditions conducive to the establishment of white mulberry. Though 1 review states that white mulberry cannot grow in shade (review by [30]), there are reports of white mulberry seedlings establishing under the cover of other vegetation [45,50,103]. In some areas, both natural [98,182] and anthropogenic [45,54,80,112,114,170,178] disturbances appear to favor the establishment of white mulberry, though not in all cases (e.g., see [70]). See Successional Status for additional information regarding white mulberry light preferences and response to disturbance.
Growth rate: A manual to woody landscaping plants reports that white mulberry has a fast growth rate, growing 10 to 12 feet (3-4 m) over a 4- to 6-year period (review by [33]).
White mulberry seedling.White mulberry is not restricted to any particular successional stage, occurring in early [45,54,103,112], mid-successional [9,47,89,115,117,121,175], and mature [169,171] plant communities. In some instances, white mulberry established secondarily after other woody species established and provided perches for seed-dispersing birds [45,102,103].
Light: White mulberry tolerates both open and shady conditions. A review states that it cannot grow in shade [30], and a manual to woody landscaping plants reports that it tolerates full sun to light shade [33]. In Ontario, white mulberry was generally found in more open conditions than the native red mulberry [18]. White mulberry seedlings grown in experimental field plots in Nebraska had a 53% higher growth rate when grown in sun compared to shade [100].
Though white mulberry may grow better in open conditions, it is commonly found in low-light areas such as canyon bottoms in west-central Oklahoma [93], lowland forests in southern Illinois [104], and old-growth oak-hickory forests in Indiana [171]. White mulberry seedlings established under the cover of planted pine groves in northeastern Kansas [50], eastern cottonwood in New York [103], and staghorn sumac in southwestern Michigan [45].
Disturbance: There is some evidence that disturbance is conducive to white mulberry establishment, though not in all cases.
Natural disturbance: In southeastern Iowa, white mulberry occurred in silver maple-eastern cottonwood floodplain plant communities, though only in gaps created by dead elms [98]. In contrast, in north-central Virginia, white mulberry had not established in debris avalanche areas 10 years after the disturbance, but was present in nearby reference mixed-hardwood forest [70]. Near Bronx, New York, white mulberry occurred as a relatively common species along edges and in gaps of both black locust and oak-maple plant communities [182]. In north-central Ohio, white mulberry was found in second-growth but not old-growth hardwood forests [175]. White mulberry also established in disturbed forests in Wisconsin [29] and Ontario [37], though no mechanism of disturbance was reported.
White mulberry occurs in many floodplain or riparian forests prone to flooding [6,16,26,35,36,47,61,75,109]. In central Ohio, white mulberry occurred in riparian bottomland forests experiencing groundwater flooding 1 to several times per year [36]. In central Missouri, white mulberry occurred on floodplain oak-hickory forests where inundation could last as long as 1 week [35]. In streamside forests in central Illinois, white mulberry occurred only at those elevational gradients experiencing flooding in 13% to 25% of years but was not present in areas experiencing more frequent flooding [6].
White mulberry is drought tolerant ([17,64,138], reviews by [30,33]), which may be attributed to its well-developed root system [138]. In the southern high plains of Oklahoma, 32.8% of planted white mulberry survived 7 years of drought [17].
Anthropogenic disturbance: In extreme southern Illinois, white mulberry established following salvage-logging after a tornado in a bottomland hardwood forest. It was not found in undisturbed forest or tornado-impacted areas without salvage logging [114]. In central Arizona, white mulberry was frequent on mesquite (Prosopis sp.) terraces characterized as "severely disturbed" following mesquite removal [178]. In southeastern Louisiana, white mulberry established on elevated spoil banks within the bottomland hardwood forest plant community [170]. White mulberry occurred at low levels on a 15- to 20-year-old revegetating lead and zinc mine spoil site in northeastern Oklahoma [54]. White mulberry established on 5- to 9-year-old revegetating landfill sites in South Korea [80]. White mulberry also established following old field abandonment in New Jersey [112] and southwestern Michigan [45].
Successional role: While 1 review suggests that white mulberry has the potential to exclude native vegetation [51], there is little documentation of this impact occurring. White mulberry would most likely alter successional trajectories where it develops in dense thickets, a relatively infrequent establishment pattern. However, on a dredge spoil island in South Carolina, white mulberry established in a thicket so dense that understory vegetation was suppressed [120].
The scientific name of white mulberry is Morus alba L. (Moraceae) [44,72].
In North America, white mulberry hybridizes with the native red mulberry (M. rubra)
([18,153,171,174], review by [30]).
Both species are highly variable and frequently confused with each other [44].
Numerous white mulberry cultivars occur in North America ([11,32,41], review by [33]).
