Pacific Island Ecosystems at Risk (PIER)

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Salix nigra
Marshall, Salicaceae
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Primarily a threat at high elevations?  no

Risk assessment results:  Evaluate; score: 5 (Hawaii-Pacific Weed Risk Assessment for Salix nigra)

Other Latin names:  Amerina caroliniana Raf.; Amerina houstoniana Raf.; Amerina nigra Raf.; Salix ambigua Pursh; Salix denudata Raf.; Salix dubia Trautv.; Salix falcata Pursh; Salix flavovirens Hornem.; Salix ligustrina F. Michx.; Salix ludoviciana Raf.; Salix marginata Wimm. ex Andersson; Salix purshiana Spreng.

Common name(s): [more details]

English: American willow, Brittle willow, Champlain willow, Dudley willow, Gooding willow, Texas black willow, black willow, gulf black willow, puzzle willow, rough American willow, sauce, saule, saule noir, sauz, scythe-leaf willow, scythe-leaved willow, southwestern black willow, swamp walnut, swamp willow, tall black willow, weide, western black willow, wilg, willow, willow catkins

Habit:  tree

Description:  "In the North [PIER ed.: U.S.], a small to medium-size tree, 9-18 m (30-60 ft) tall; on better sites in the South, a tall tree to 42 m (138 ft), with a tall, straight trunk up to 2 m (6.6 ft) wide supporting a broadly irregular crown. Bark: heavy, black or very dark brown, deeply and narrowly cracked, becoming shaggy in old age. Branches: thick, upright, spreadying, and red-brown or grayish branchlets that are downy when they are new, later smooth and breaking easily at the joints. Winter buds: pointed, about 3-4 mm (about 0.1-0.2 in) long. Leaves: alternate, deciduous, simple, 7.5-15 cm (3-6 in) long, 8-18 mm (0.3-0.7&nbnsp;in) wide, lance-shaped, long-pointed with a wedge-shaped or rounded base, finely toothed, thin and papery, bright green above, paler below, leafstalks short; stipules wing-like at base of leaf. Flowers: male and female catkins borne upright on ends of short, leafy branchlets on separate trees, 2.5-7.5 cm (1-3 in) long, scales yellow, broadest near their blunted tips and hairy on the inner surface. Male flowers with 3 to 5 stamens; female flowers with an oval-shaped ovary, short-stalked, dividing slightly into 2 stigma lobes. Fruits: capsules egg-shaped, 4-8 mm (0.1-0.3 mm) long, light reddish-brown, containing many tiny, silky-haired seeds." (Trees of North America, pp. 489-490)

Habitat/ecology:  "This species (PIER ed.: Salix nigra Marshall) is usually found on moist or wet soils along banks of streams, lakes, swamps around farm ponds, and pasture sloughs. ... ¶Black willow is adapted wherever ample soil moisture is found. Black willow grows best where the average annual rainfall is 51 inches, of which 20 inches falls during the growing season, April through August." (USDA/NRCS, p. 1)

"Old black willows [PIER ed.: Salix nigra] rank among the largest willows in the world, reaching great heights in swamps in the deep South; but in the north on poor sites, they are comparatively small trees. Ranging from Maine to Minnesota, and south to Texas, these trees do well on almost any soil but require a plentiful and constant supply of moisture for thei roots during the growing season. They are most common along river margins and in low, wet sites such as swamps and sloughs, and along bayous, gullies, and drainage ditches. These trees are prevalent and attain their best growth along the lower part of the Mississippi River. They form the main component of one wetlands forest type where pure stands are often formed. Black willow is found with such trees as black spruce, cottonwood, river birch, water tupelo, and bald cypress. ¶Black willow is a fast-growing, relatively short-lived tree averaging 15 m (50 ft) by 10 years of age. Flowering occurs from February to April throughout its [PIER ed.: native] range, at about the same time as the leaves unfolding. Seed production begins at age 10, though prime production is from 25 to 75 years. Good crops are borne almost every year. Deer and rodents browse the shoots, and spsuckers feed on the inner bark." (Trees of North America, pp. 488-489)

Presented in the context of "land reclamation": "Fast stabilization of chemically degraded land surfaces and reestablishment of a biologically active soil surface can be achieved using Salix species, which possess the major requirements for plant survival in environmentally disrupted areas: /acid, wetness and, for some species, drought tolerance (Logan, 1992), low nutrient requirements for many species, and an ability to bud, root, and resprout from totipotent cells at even very old nodal areas. Salix species are able to establish on waste grounds and badly degraded soils with scarce topsoil, such as industrial spoils, mines and gravel pits, spoil-heaps of lignite mines, overburdens, quarries, highly eroded soils, waste sites and roadsides (Hartwright, 1960; FAO, 1979; White, 1992; Bungart and Huttl, 2001). ¶Tolerance of soil chemical contamination is an important requirement for survival in many situations and Salix potential for reclamation can be emphasized by the fact that, of the seven most important metal contaminants in soil, Salix has been reported to have tolerance to at least four (cadmium, copper, zinc, lead) and to one (cesium) of four radionuclides (Eltrop et al., 1991; Sennerby-Forsse et al., 1993; Punshon and Dickinson, 1997). ¶Willows will colonize open areas naturally (Schramm, 1966; Clewell, 1999), but as with other natural processes this early succession is spatially random and temporally unpredictable. With strategic planting of willows into disrupted landscapes and some assistance at early stages, restoration is achieved more quickly. For rapid establishment of plant cover willows can be used in the forms of mats, stakes, rooted cuttings and stumps with root masses. Low cost plantings of Salix and facilitation of the processes of land rehabilitation by altering microclimate, reducing runoff, providing ecologically diverse wildlife habitats and enhancing human recreational areas comply with new reclamation laws in many states and growing public concerns over wasteland management." (Willows beyond wetlands, p. 188)

Propagation:  "Black willow is easily established from cuttings. Stringent requirements of seed germination and seedling establishment limit black willow to wet soils. ... ¶Good seed crops occur almost every year with only a few interspersed poor crop years. The seeds are widely disseminated by wind and water. Willow seed must be collected as soon as it ripens and sown immediately. Stem cuttings are highly desirable to propagate trees." (USDA/NRCS, p. 2)

"Seed Production and Dissemination- Seed production usually starts when the trees are about 10 years old, although viable seeds can be obtained at younger ages. Optimum seed-bearing age is from 25 to 75 years. The trees have good seed crops almost every year, with only a few interspersed poor crops and rare failures resulting from late freezes after flower buds have begun to open. Large volumes of seeds are produced; they average 5 million/kg (2.3 million/lb). When the seeds fall, the long silky hairs act as wings to carry the seeds very long distances. The seeds are widely disseminated by wind and water. ¶Seedling Development- Unless the willow seed is floating on water, it must reach the seedbed within 12 to 24 hours because viability is greatly reduced by only a few days of dry conditions. Germination is epigeal. Germinative capacity is usually high and no dormancy is known. Very moist, almost flooded exposed mineral soil is best for satisfactory germination and early development. Full light promotes vigorous growth once the seedling is well established. In a favorable environment, seedlings grow rapidly-often exceeding 1.2 in (4 ft) in height the first year (4). *Seed Production and Dissemination- Seed production usually starts when the trees are about 10 years old, although viable seeds can be obtained at younger ages. Optimum seed-bearing age is from 25 to 75 years. The trees have good seed crops almost every year, with only a few interspersed poor crops and rare failures resulting from late freezes after flower buds have begun to open. Large volumes of seeds are produced; they average 5 million/kg (2.3 million/lb). When the seeds fall, the long silky hairs act as wings to carry the seeds very long distances. The seeds are widely disseminated by wind and water. ¶Seedling Development- Unless the willow seed is floating on water, it must reach the seedbed within 12 to 24 hours because viability is greatly reduced by only a few days of dry conditions. Germination is epigeal. Germinative capacity is usually high and no dormancy is known. Very moist, almost flooded exposed mineral soil is best for satisfactory germination and early development. Full light promotes vigorous growth once the seedling is well established. In a favorable environment, seedlings grow rapidly-often exceeding 1.2 in (4 ft) in height the first year (4). ¶Seedlings grow best when there is abundant moisture available throughout the growing season. In the Mississippi Valley, average heights are 9.8 in (32 ft) and average breast-high diameters are 6.6 cm (2.6 in) when the saplings are 5 years old (4). ¶Vegetative Reproduction- Root stocks of very young willow trees sprout prolifically. Propagation by cuttings is the usual method of artificial regeneration. With adequate moisture, good cuttings, and sufficient cultivation to reduce competition from other vegetation, first-year plantation survival can be close to 100 percent. Post-size willow cuttings have been rooted for use in flood projects to prevent gullies (4). ¶Seedlings grow best when there is abundant moisture available throughout the growing season. In the Mississippi Valley, average heights are 9.8 in (32 ft) and average breast-high diameters are 6.6 cm (2.6 in) when the saplings are 5 years old (4). ¶Vegetative Reproduction- Root stocks of very young willow trees sprout prolifically. Propagation by cuttings is the usual method of artificial regeneration. With adequate moisture, good cuttings, and sufficient cultivation to reduce competition from other vegetation, first-year plantation survival can be close to 100 percent. Post-size willow cuttings have been rooted for use in flood projects to prevent gullies (4)." (Silvics of North America (USDA/FS) [Salix&nbps;nigra])

"Flowering occurs from February to April throughout its [PIER ed.: native] range, at about the same time as the leaves unfolding. Seed production begins at age 10, though prime production is from 25 to 75 years. Good crops are borne almost every year. Deer and rodents browse the shoots, and spsuckers feed on the inner bark." (Trees of North America, p. 489)

"The common ecological restriction of Salix to wetlands and floodplains reflects an environment with constant moisture supply for immediate seed germination (Dorn, 1976). Moisture availability at the time of seed dispersal is critical because seeds of Salix are viable for only a few weeks (McLeod and McPherson, 1973; Maroder et al., 2000); this can be a limiting factor in regions with dry conditions in late spring. However, after seedling establishment, constant soil moisture is not as important to survival of many willow species (Skvortsov, 1999)." (Willows beyond wetlands, p. 185)

Native range:  The native range of Salix nigra includes roughly the eastern half of U.S.A. (excluding peninsular Florida), southward into the northeastern edge of Mexico, and northward into the southeastern tip of Canada (Trees of North America, range map, p. 489; (GRIN)). According to GRIN, the the native range includes eastern Canada and the eastern United States, to Texas in the southwest of its range.

Impacts and invaded habitats:  "Black willow (Salix nigra Marshall) is a flood-tolerant tree native to the southeastern United States and recently invasive in Australia, where it is considered detrimental to riparian environments." (Stokes 2008)

"[Salix nigra] . . . suckers freely and will also quickly block drains or septic systems. It has formed dense stands in disturbed wetlands on the Swan Coastal Plain [Western Australia]." (Western Weeds, p. 230)

"Introduced willows can become invasive pests in Australia": concern has grown over the past decade about their [PIER ed.: Salix spp.] invasive natural spread in the water courses of southeastern Australia. The main environmental effects include obstruction and diversion of streams and hence erosion, extensive displacement of native vegetation with loss of biodiversity, and reductions in the quantity and quality of water." (Kremer 2003)

In New South Wales (Australia): "Black willow (Salix nigra). . . . Black willow is an invasive woody weed of rivers, streams and wetlands throughout temperate Australia. It is considered one of the most serious weeds of riparian and wetland ecosystems in Australia, where it spreads quickly and forms dense stands along water courses. . . . Black willows were originally planted during the 1960s for soil stabilisation projects along streams and river banks in Victoria and southern NSW. They are now considered to cause erosion and flooding, and reduce water availability and quality." (NSW Weedwise)

In New South Wales (Australia): "Black willow (Salix nigra). . . . ¶How does it spread? ¶Black willow spreads mostly from seed but can also grow from broken stems. A female tree produces thousands of light fluffy seeds each year that can travel by wind or water. Seeds will only survive for a couple of weeks, yet under ideal conditions (bare wet ground in full sunlight) germination is fast and a mass of seedlings may be seen in about a month. ¶Stem fragments may break off and travel many kilometers downstream. New roots will grow in water from these fragments, resulting in new infestations. ¶Black willow is able to hybridise (cross-pollinate) and breed with other willow species. This may increase problems caused by other Salix species." (NSW Weedwise)

An "Impact Assessment - Black Willow (Salix nigra) in Victoria (Nox)" is presented online by Agriculture Victoria detailing various aspects of impacts of Salix nigra in that Australian state.

In New South Wales (Australia): "Black willow (Salix nigra). . .Black willow is an invasive tree of rivers, streams and wetlands. It is considered one of the most serious weeds of riparian and wetland ecosystems in Australia. It is a Weed of National Significance." (NSW Weedwise)

Presence:

Pacific Rim
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Australia
Australia
Australia introduced
invasive
Stokes, Kate A. (2008)
accessed 20181121
Also reported from
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Canada
Canada
Canada native
cultivated
U.S. National Plant Germplasm System (year unknown)
accessed 20181121, see ref for distribution details
Canada
Canada
Canada (eastern) native
USDA/NRCS (year unknown)
accessed 20181121
Canada
Canada
Canada (eastern)   iNaturalist (year unknown)
accessed 20181121
Canada
Canada
Canada (western)   iNaturalist (year unknown)
accessed 20181121
Europe
Europe
France cultivated
iNaturalist (2018)
accessed 20181121
Europe
Europe
Germany   iNaturalist (2018)
accessed 20181121
South America
South America
Argentina cultivated
iNaturalist (2018)
accessed 20181121
United States of America
United States
United States native
cultivated
U.S. National Plant Germplasm System (year unknown)
accessed 20181121
United States of America
United States
United States (eastern) native
USDA/NRCS (year unknown)
accessed 20181121
United States of America
United States
United States (eastern)   iNaturalist (year unknown)
accessed 20181121
United States of America
United States
United States (western)   iNaturalist (year unknown)
accessed 20181121
United States (continental except west coast)
United States (other states)
USA (Florida) native
cultivated
U.S. National Plant Germplasm System (year unknown)
accessed 20181121, see ref for distribution details, "also cultivated" (but not necessarily specifically in Florida)

Comments:  "Black willow is very susceptible to fire. Hot fires can kill entire stands of willows. Black willow will sprout at the base following fire" (USDA/NRCS, p. 2)

GRIN notes that Salix nigra is cultivated, and is used as an ornamental, for erosion control, and as a food source for honeybees (among other uses).

Control:  In Australia: "Methods of Control. The main method is injection of stems with the weedicide Glyphosate. Details of this and other methods are given in Cremer (1999) and in Trounce and Cremer (1997). Painting of freshly cut stems with Glyphosate is particularly effective and the spraying of foliage of shorter plants (< 2 m tall) is often effective as well. ¶Biocontrol is being considered." (Kremer 2003, p. 23)

In New South Wales (Australia): "Black willow (Salix nigra). . . . ¶Control ¶. . . Very few herbicides are registered for use near water and extreme care must be taken to avoid contact with any non-target species. ¶Herbicide options ¶WARNING - ALWAYS READ THE LABEL." Herbicides/methods suggested: Glyphosate 360 g/L (Roundup®); Rate: 1.0–1.3 L in 100 L of water; Comments: Spray to wet all foliage. Use the higher rate for trees 1–2 m high; Withholding period: Nil; Herbicide group: M, Inhibitors of EPSP synthase; Resistance risk: Moderate. Glyphosate 360 g/L (Roundup®); Rate: Undiluted; Comments: Stem injection; Withholding period: Nil; Herbicide group: M, Inhibitors of EPSP synthase; Resistance risk: Moderate. Picloram 44.7 g/kg + Aminopyralid 4.47 g/L (Vigilant II ®); Rate: Undiluted; Comments: Cut stump/stem injection application. Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm; Withholding period: Nil; Herbicide group: I, Disruptors of plant cell growth (synthetic auxins); Resistance risk: Moderate. Triclopyr 240 g/L + Picloram 120 g/L (Access™ ); Rate: 1.0 L per 15 L of diesel; Comments: Cut stump application method; Withholding period: Nil; Herbicide group: I, Disruptors of plant cell growth (synthetic auxins); Resistance risk: Moderate. (NSW Weedwise)


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This page was created on 12 SEP 2017 and was last updated on 21 NOV 2018.