Research directed by C. Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service

Information on Risk Assessments
Original risk assessment

Salix babylonica; Babylon weeping willow

Answer

1.01

Is the species highly domesticated?

y=-3, n=0

1.02

Has the species become naturalized where grown?

y=-1, n=-1

y

1.03

Does the species have weedy races?

y=-1, n=-1

n

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

1

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

1

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

y

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

2.05

Does the species have a history of repeated introductions outside its natural range? y=-2

?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

y

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

n

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

n

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

y

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

y

4.01

Produces spines, thorns or burrs

y=1, n=0

n

4.02

Allelopathic

y=1, n=0

4.03

Parasitic

y=1, n=0

n

4.04

Unpalatable to grazing animals

y=1, n=-1

n

4.05

Toxic to animals

y=1, n=0

n

4.06

Host for recognized pests and pathogens

y=1, n=0

y

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

n

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

n

4.1

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

y

4.11

Climbing or smothering growth habit

y=1, n=0

n

4.12

Forms dense thickets

y=1, n=0

5.01

Aquatic

y=5, n=0

n

5.02

Grass

y=1, n=0

n

5.03

Nitrogen fixing woody plant

y=1, n=0

n

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

6.02

Produces viable seed.

y=1, n=-1

y

6.03

Hybridizes naturally

y=1, n=-1

y

6.04

Self-compatible or apomictic

y=1, n=-1

n

6.05

Requires specialist pollinators

y=-1, n=0

n

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

y

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

3

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

n

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

n

7.04

Propagules adapted to wind dispersal

y=1, n=-1

y

7.05

Propagules water dispersed

y=1, n=-1

y

7.06

Propagules bird dispersed

y=1, n=-1

n

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

n

7.08

Propagules survive passage through the gut

y=1, n=-1

n

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

y

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

n

8.03

Well controlled by herbicides

y=-1, n=1

y

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

y

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

Total score:

9

Source

Notes

1.01

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Weeping willow has been cultivated for more than 3000 years in China

1.02

USDA, ARS, National Genetic Resources Program.
Germplasm Resources Information Network - (GRIN)
[Online Database].
National Germplasm Resources Laboratory, Beltsville, Maryland.
URL: http://www.ars-grin.gov/var/apache/cgi-bin/npgs/html/tax_search.pl?Salix+babylonica (16 December 2003)

widely cultivated & naturalized

1.03

no evidence

2.01

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

S. babylonica originates from arid and semiarid regions of central and northern China (Skvortsov, 1999). It is found mainly in the plains south of the Yangtze River valley, extending from Guangdong province in the south to the Yunnan-Guizhou plateau in the west. It can grow in the warm river valley at altitudes above 2000 m (Zheng, 1978; Tu, 1982).
Natural latitude range: Approximate limits north to south: 37N to 25N
Climate
Weeping willow is widely distributed in subtropical, warm temperate and temperate zones. The climate should not be too cold in winter with an average temperature no less than 0C in January. Ideal summer conditions are hot and wet with an average temperature of 27 C in July and an extreme maximum temperature of 40.5 C However, S. babylonica also grows very well in introduced areas, such as Harbin where there is an average temperature of -17.9 C in January and an extreme minimum temperature of -38.1 C. The precipitation is over 1000 mm. It can grow well in arid areas as long as there is suf

2.02

2.03

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

S. babylonica originates from arid and semiarid regions of central and northern China (Skvortsov, 1999). It is found mainly in the plains south of the Yangtze River valley, extending from Guangdong province in the south to the Yunnan-Guizhou plateau in the west. It can grow in the warm river valley at altitudes above 2000 m (Zheng, 1978; Tu, 1982).
Natural latitude range: Approximate limits north to south: 37N to 25N

2.04

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

S. babylonica originates from arid and semiarid regions of central and northern China (Skvortsov, 1999). It is found mainly in the plains south of the Yangtze River valley, extending from Guangdong province in the south to the Yunnan-Guizhou plateau in the west. It can grow in the warm river valley at altitudes above 2000 m (Zheng, 1978; Tu, 1982).
Natural latitude range: Approximate limits north to south: 37N to 25N

2.05

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

It was introduced for ornamental purposes to numerous Asian, European and North American countries, for example by 1676 it was in Western Anatolia, and by 1730 in England (Bean, 1980).
Weeping willow is cultivated nearly everywhere in temperate regions of the world. In Eurasia, northernmost localities of successful cultivation match the limits of commercial peach orchards, and include: southern UK, southern Germany, Hungary, the Crimea and the Caucasus, Uzbekistan, and most of the Korean peninsula and Japan (Skvortsov, 1999). It was introduced into Europe from the Near East in the 18th century (Skvortsov, 1999), and subsequently to American countries. In Argentina and New Zealand, it was introduced for plantation forests and for tree breeding and hybridization purposes (Petray et al., 1997; Kraayenoord et al., 1995).

3.01

USDA, ARS, National Genetic Resources Program.
Germplasm Resources Information Network - (GRIN)
[Online Database].
National Germplasm Resources Laboratory, Beltsville, Maryland.
URL: http://www.ars-grin.gov/var/apache/cgi-bin/npgs/html/tax_search.pl?Salix+babylonica (16 December 2003)

widely cultivated & naturalized

3.02

no evidence

3.03

no evidence

3.04

(1)Henderson, L. (1991) Alien invasive Salix spp. (willows) in the grassland biome of South Africa. South African Forestry Journal, 1991, No.157, pp.91-95, 23 ref. (2)Randall, R. 2001. Garden thugs, a national list of invasive and potentially invasive garden plants. Plant Protection Quarterly 16:138-171. (3)http://conservation.ipswich.qld.gov.au/conservation/rebate.htm

(1) Roadside surveys of alien plant invaders in the grasslands (veld) of the Transvaal, Natal, Orange Free State and E. Cape showed that several alien Salix spp. are naturalized along watercourses in these regions. Salix babylonica, the most widespread woody riverine invader, and S. fragilis, one of the basket willows, are the most prominent species. S. fragilis is less widely distributed than S. babylonica but is prominent in the high grasslands of NE Orange Free State, S. Natal and NE Cape. Both species have, in places, formed pure stands along whole river reaches. Although S. babylonica has been planted at dams and along riverbanks, its extensive occurrence along watercourses is most likely due to self (vegetative) propagation and dispersal by floodwaters. It is probable that S. fragilis is propagated and dispersed in the same manner. Although aesthetically pleasing and having many beneficial qualities, the alien willows pose a potential threat to the conservation of indigenous riparian species and may alt

3.05

Randall, R. 2001. Garden thugs, a national list of invasive and potentially invasive garden plants. Plant Protection Quarterly 16:138-171.

Several Salix species are listed

4.01

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

no description of these traits

4.02

Koul, V. K.; Raina, A.; Khanna, Y. P.; Tickoo, M. L.; Singh, H. (1991) Evaluation of allelopathic influence of certain farm grown tree species on rice (Oryza sativa L. c.v. PC 19). Indian Journal of Forestry, 1991, Vol.14, No.1, pp.54-57, 13 ref.

AB: Laboratory experiments were conducted to investigate the allelopathic activity of leaf leachates of 8 commonly grown farm tree species (Acacia nilotica, Dalbergia sissoo, Bauhinia variegata, Ficus bengalensis [F. benghalensis], Morus alba, Populus deltoides, Salix babylonica and Leucaena leucocephala ) on seed germination and early growth of rice. In general all leaf leachates inhibited seed germination with maximum reduction from L. leucocephala . A. nilotica promoted seedling growth. [LAB only]

4.03

no evidence

4.04

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

The leaves and tender shoots are used as fodder for cows and goats in some areas.

4.05

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

The leaves and tender shoots are used as fodder for cows and goats in some areas.

4.06

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Protection
Insect pests
Anoplophora glabripennis, Apriona germart, Anoplophora chinensis, Rabdophaga sp., Plagiodera versicolora and Batocera lineonata attack weeping willow heavily. Adults feed on fresh bark and larvae bore into trunks and branches. Injured trees often break in strong winds. These insect pests can be effectively controlled using insecticides (trichlorfon, Dibrom, fenitrothion), biological pesticides (Bacillus thuringiensis), physical methods (light traps) and artificial capture. Willow beetles (Phratora vulgatissima and P. vitellinae) can damage S. babylonica in short-rotation stands (Kendall and Wiltshire, 1996).
Fungal diseases
Willow rust (Melampsora coleosporioides) usually occurs in willow seedlings and juvenile stands. Bordeaux mixture and some silvicultural practices, such as thinning and proper irrigation, are usually practised (Zheng, 1978). Willow anthracnose (Drepanopeziza sphaeroides) damages Salix species in New Zealand (Spiers and Hathaway, 1988).
[many pests also attack other

4.07

no evidence

4.08

considered a fire-retardant tree

http://www.glenforrestfirebrigade.org/species.asp

4.09

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Weeping willow is a light-demanding species, so it has difficulty regenerating under forest canopy

4.1

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

In its natural distribution area, S. babylonica is found growing along rivers, on damp valley bottoms, and in depressions amidst sand (Skvortsov, 1999). S. babylonica can grow on a variety of soils, such as solonetz and acid soils, sand and sludge deposit soils on beaches, and some salty soils (salt content 0.2%) in coastal areas. Around lakes and beaches, weeping willow often forms a mixed willow-reed plant community.
Descriptors
- Soil texture: light; medium; heavy
- Soil drainage: free; impeded; seasonally waterlogged
- Soil reaction: neutral; alkaline
- Special soil tolerances: saline; infertile
- Soil types: alkaline soils; alluvial soils; cambisols; fluvisols; loess soils; luvisols; hydromorphic soils; sandy soils; solods

4.11

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

10-20 m tall tree with a stem d.b.h. of 60-80 cm.

4.12

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

10-20 m tall tree with a stem d.b.h. of 60-80 cm. Crown is small, open and loose. Stem furrowed, usually dividing near the ground, producing a wide spreading flattened crown, from which long slender branchlets carrying the leaves hang perpendicularly in a dense curtain. Branches are thin and short, free of pubescence, arching outward. Annual branch growth very long and nearly string-like, pendulous, occasionally erect. [may form stand along riverbanks, but not usually referred to as thickets]

5.01

terrestrial to riparian

5.02

tree; Salicaceae

5.03

tree; Salicaceae

5.04

tree

6.01

no evidence

6.02

CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Weeping willow is occasionally propagated by seed. The seed is very small (weight of 1000 seeds about 0.15 g). Germination capacity is sharply reduced if seed is stored improperly; the viability of air-dry seed is 5-10 days. Therefore, seeds should be sown on moist nursery beds immediately after collection. At 20-25 C, fresh leaves expand and fine rhizoids appear 24 hours after sowing. Primary roots and real leaves appear 3 and 10 days after sowing, respectively.

6.03

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Natural hybrids appear very commonly in both natural and cultivated willow geographical distribution areas. Some hybrids (S. babylonica x S. alba, S. babylonica x S. fragilis) form naturally, and wild weeping willow populations exhibit wide genetic variation. In China, some superior phenotypes have been successfully selected from natural weeping willow populations aged 2 or 3 years old (Tu, 1982, 1997; Pan, 1997).

6.04

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

dioecious

6.05

CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.

The flowers are a good source of honey [bee pollinated]

6.06

Henderson, L. (1991) Alien invasive Salix spp. (willows) in the grassland biome of South Africa. South African Forestry Journal, 1991, No.157, pp.91-95, 23 ref.

" S. babylonica has been planted at dams and along riverbanks, its extensive occurrence along watercourses is most likely due to self (vegetative) propagation and dispersal by floodwaters."

6.07

CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.

(1)The height of seedlings can reach 10-15 cm with 3-4 pairs of alternate leaves after one month and 200 cm after one year (2) A Fast Growing Deciduous Tree [minimum estimate for a fast growing large tree]

7.01

no evidence

7.02

CAB International, (2000) Forestry Compendium Global Module. Wallingford, UK: CAB International.

It was introduced for ornamental purposes to numerous Asian, European and North American countries, for example by 1676 it was in Western Anatolia, and by 1730 in England (Bean, 1980).
Weeping willow is cultivated nearly everywhere in temperate regions of the world. In Eurasia, northernmost localities of successful cultivation match the limits of commercial peach orchards, and include: southern UK, southern Germany, Hungary, the Crimea and the Caucasus, Uzbekistan, and most of the Korean peninsula and Japan (Skvortsov, 1999). It was introduced into Europe from the Near East in the 18th century (Skvortsov, 1999), and subsequently to American countries. In Argentina and New Zealand, it was introduced for plantation forests and for tree breeding and hybridization purposes (Petray et al., 1997; Kraayenoord et al., 1995).

7.03

no evidence

7.04

(1) CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.
(2) http://home.earthlink.net/~wilhelmina_d/bos/herbal_willow.html

(1) The seed is very small (weight of 1000 seeds about 0.15 g). (2) The fruits of willows and poplars are small capsules containing numerous seeds, each of which has cottonlike threads that act as parachutes, aiding in wind dispersal.

7.05

Henderson, L. (1991) Alien invasive Salix spp. (willows) in the grassland biome of South Africa. South African Forestry Journal, 1991, No.157, pp.91-95, 23 ref.

AB: Roadside surveys of alien plant invaders in the grasslands (veld) of the Transvaal, Natal, Orange Free State and E. Cape showed that several alien Salix spp. are naturalized along watercourses in these regions. Salix babylonica, the most widespread woody riverine invader, and S. fragilis, one of the basket willows, are the most prominent species. S. fragilis is less widely distributed than S. babylonica but is prominent in the high grasslands of NE Orange Free State, S. Natal and NE Cape. Both species have, in places, formed pure stands along whole river reaches. Although S. babylonica has been planted at dams and along riverbanks, its extensive occurrence along watercourses is most likely due to self (vegetative) propagation and dispersal by floodwaters. It is probable that S. fragilis is propagated and dispersed in the same manner. Although aesthetically pleasing and having many beneficial qualities, the alien willows pose a potential threat to the conservation of indigenous riparian species and may al

7.06

no evidence

7.07

no evidence

7.08

no evidence of consumption

8.01

CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.

The seed is very small (weight of 1000 seeds about 0.15 g).

8.02

(1)CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International. (2)http://www.gardenbed.com/s/3479.cfm

(1)Germination capacity is sharply reduced if seed is stored improperly; the viability of air-dry seed is 5-10 days. Therefore, seeds should be sown on moist nursery beds immediately after collection. At 20-25 C, fresh leaves expand and fine rhizoids appear 24 hours after sowing. Primary roots and real leaves appear 3 and 10 days after sowing, respectively. (2)Seed - must be surface sown as soon as it is ripe in late spring. It has a very short viability, perhaps as little as a few days.

8.03

EDuffy, S. L. (1972) A split-root tetrazolium method for evaluating effectiveness and phytotoxicity of root-active herbicides. Weed Research, 1972, Vol.12, No.2, pp.169-173

(1)Copper sulphate and sodium hydroxide were used to test the performance of a split-root method for evaluating the effectiveness and phytotoxicity of root-active herbicides. The root system of weeping willow (Salix babylonica) cuttings was separated vertically and placed in adjacent containers so that one section was immersed in half-strength Hewitt's medium containing 26.5 g herbicide/litre and the other in untreated medium. The roots were assayed with 2,3,5-triphenyltetrazolium chloride 24 h after treatment to determine their viability. The effectiveness of the test herbicide was then inversely proportional to the quantity of formazan extracted from the treated roots expressed as a percentage of that extracted from the controls. Both compounds effectively reduced the viability of the roots by at least 70%. Copper sulphate was systemic and injured untreated plant parts when 39% of the root system was exposed while sodium hydroxide affected only the treated roots. The technique is relatively rapid and does n

8.04

CAB International, (2001) Forestry Compendium Global Module. Wallingford, UK: CAB International.

Weeping willow has a very strong capacity to sprout. Young shoots can reach 3 m high in one growing season. Thus, sprouting stands will gradually form when trees are harvested by clearcutting.

8.05

no evidence