Plant Assessment Form

More Ilex aquifolium resources

Ilex aquifolium

Common Names: English holly

Evaluated on: 8/17/04

List committee review date: 27/08/2004

Re-evaluation date:

Evaluator(s)

Joseph M. DiTomaso/Extension Specialist
University of California, Davis
Weed Science Program, Robbins Hall, Davis, CA 95616
530-754-8715
ditomaso@vegmail.ucdavis.edu

List committee members

Alison Stanton
Peter Warner
Jake Sigg
Joe DiTomaso
John Randall
Cynthia Roye

General Comments

The amount of information on the invasiveness and biology of this species is very limited.

Table 2. Criteria, Section, and Overall Scores

Overall Score? Limited

Alert Status? No Alert

Documentation? 3 out of 5

Score

Documentation

1.1

?Impact on abiotic ecosystem processes

U. Unknown

Reviewed Scientific Publication

Impact?
Four-part score UBDD Total Score
C

1.2

?Impact on plant community

B. Moderate

Other Published Material

1.3

?Impact on higher trophic levels

D. Negligible

Other Published Material

1.4

?Impact on genetic integrity

D. None

Other Published Material

2.1

?Role of anthropogenic and natural disturbance in establishment

B. Moderate

Observational

Invasiveness?
Total Points
14 Total Score B

2.2

?Local rate of spread with no management

B. Increases less rapidly

Other Published Material

2.3

?Recent trend in total area infested within state

B. Increasing less rapidly

Other Published Material

2.4

?Innate reproductive potential
(see Worksheet A)

C. Low

Other Published Material

2.5

?Potential for human-caused dispersal

A. High

Other Published Material

2.6

? Potential for natural long-distance dispersal

A. Frequent

Reviewed Scientific Publication

2.7

?Other regions invaded

C. Already invaded

Other Published Material

3.1

?Ecological amplitude/Range
(see Worksheet C)

B. Moderate

Other Published Material

Distribution?
Total Score C

3.2

?Distribution/Peak frequency
(see Worksheet C)

D. Very low

Observational

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? Consider the impact on the natural range and variation of abiotic ecosystem processes and system-wide parameters in ways that significantly diminish the ability of native species to survive and reproduce. Alterations that determine the types of communities that can exist in a given area are of greatest concern. Examples of abiotic processes include: - fire occurrence, frequency, and intensity; - geomorphological changes such as erosion and sedimentation rates; - hydrological regimes, including soil water table; - nutrient and mineral dynamics, including salinity, alkalinity, and pH; - light availability (e.g. when an aquatic invader covers an entire water body that would otherwise be open). Select the one letter below that best describes this species' most severe impact on an abiotic ecosystem process: A. Severe, possibly irreversible, alteration or disruption of an ecosystem process. B. Moderate alteration of an ecosystem process. C. Minor alteration of an ecosystem process. D. Negligible perceived impact on an ecosystem process. U. Unknown.	U Reviewed Scientific Publication
Identify ecosystem processes impacted: No information available. Sources of information:
Question 1.2 Impact on plant community composition, structure, and interactions? Consider the cumulative ecological impact of this species to the plant communities it invades. Give more weight to changes in plant composition, structure, and interactions that involve rare or keystone species or rare community types. Examples of severe impacts include: - formation of stands dominated (>75% cover) by the species; - occlusion (>75% cover) of a native canopy, including a water surface, that eliminates or degrades layers below; - significant reduction or extirpation of populations of one or more native species. Examples of impacts usually less than severe include: - reduction in propagule dispersal, seedling recruitment, or survivorship of native species; - creation of a new structural layer, including substantial thatch or litter, without elimination or replacement of a pre-existing layer; - change in density or depth of a structural layer; - change in horizontal distribution patterns or fragmentation of a native community; - creation of a vector or intermediate host of pests or pathogens that infect native plant species. Select the one letter below that best describes this species' impact on community composition, structure and interactions: A. Severe alteration of plant community composition, structure, or interactions. B. Moderate alteration of plant community composition. C. Minor alteration of community composition. D. Negligible impact known; causes no perceivable change in community composition, structure, or interactions. U. Unknown.	B Other Published Material
Identify type of impact or alteration: The effets of English holly on native species and communities in the Northwest are unknown because of the fairly recent onset of the invasions. However, the plant is causing concern because it is increasingly appearing in the now rare ancient forests of the region. It changes the character and structure of these forests, adding a tall shrub layer that is not normally found. Sources of information: Reichard, S. 1966. Ilex aquifolium. Page 57, In Invasive Plants. Weeds of the Global Garden. Randall, J.M. and J. Marinelli, eds., Brooklyn Botanical Garden, Brooklyn, NY.
Question 1.3 Impact on higher trophic levels? Consider the cumulative impact of this species on the animals, fungi, microbes, and other organisms in the communities that it invades. Although a non-native species may provide resources for one or a few native species (e.g. by providing food, nesting sites, etc.), the ranking should be based on the species' net impact on all native species. Give more weight to changes in composition and interactions involving rare or keystone species or rare community types. Examples of severe impacts include: - extirpation or endangerment of an existing native species or population; - elimination or significant reduction in native species' nesting or foraging sites, cover, or other critical resources (i.e., native species habitat), including migratory corridors. Examples of impacts that are usually less than severe include: - minor reduction in nesting or foraging sites, cover, etc. for native animals; - minor reduction in habitat connectivity or migratory corridors; - interference with native pollinators; - injurious components, such as awns or spines that damage the mouth and gut of native wildlife species, or production of anti-digestive or acutely toxic chemical that can poison native wildlife species. Select the one letter below that best describes this species' impact on community composition and interactions: A. Severe alteration of higher trophic populations, communities, or interactions. B. Moderate alteration of higher trophic level populations, communities, or interactions. C. Minor alteration of higher trophic level populations, communities or interactions. D. Negligible impact; causes no perceivable change in higher trophic level populations, communities, or interactions. E. Unknown.	D Other Published Material
Identify type of impact or alteration: Berries have been reported to cause digestive tract irritation in children when ingested, but animals, particularly birds seem to eat it with impunity. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press); DiTomaso, J.M. - observational
Question 1.4 Impact on genetic integrity? Consider whether the species can hybridize with and influence the proportion of individuals with non-native genes within populations of native species. Mechanisms and possible outcomes include: - production of fertile or sterile hybrids that can outcompete the native species; - production of sterile hybrids that lower the reproductive output of the native species. Select the one letter below that best describes this species' impact on genetic integrity: A. Severe (high proportion of individuals). B. Moderate (medium proportion of individuals). C. Minor (low proportion of individuals). D. No known hybridization. U. Unknown.	D Other Published Material
No native Ilex or even members of the family in the western US. Sources of information: Hickman, J.C. ed. 1993. The Jepson Manual. Higher Plants of California. UC Press, Berkeley
Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance in establishment? Assess this species' dependence on disturbance: both human and natural: for establishment in wildlands. Examples of anthropogenic disturbances include: - grazing, browsing, and rooting by domestic livestock and feral animals; - altered fire regimes, including fire suppression; - cultivation; - silvicultural practices; - altered hydrology due to dams, diversions, irrigation, etc.; - roads and trails; - construction; - nutrient loading from fertilizers, runoff, etc. Examples of natural disturbance include: - wildfire; - floods; - landslides; - windthrow; - native animal activities such as burrowing, grazing, or browsing. Select the first letter in the sequence below that describes the ability of this species to invade wildlands: A. Severe invasive potential: this species can establish independent of any known natural or anthropogenic disturbance. B. Moderate invasive potential: this species may occasionally establish in undisturbed areas but can readily establish in areas with natural disturbances. C. Low invasive potential: this species requires anthropogenic disturbance to establish. D. No perceptible invasive potential: this species does not establish in wildlands (though it may persist from former cultivation). U. Unknown.	B Other Published Material
Describe role of disturbance: Moves into undisturbed sites. Does not appear to need disturbance to become established, but moves into disturbed areas as well following logging activity. Sources of information: DiTomaso, J.M. - observational
Question 2.2 Local rate of spread with no management? Assess this species' rate of spread in existing localized infestations where the proportion of available habitat invaded is still small when no management measures are implemented. Select the one letter below that best describes the rate of spread: A. Increases rapidly (doubling in <10 years) B. Increases, but less rapidly C. Stable D. Declining U. Unknown	B Other Published Material
Describe rate of spread: Although not quantitatively measured, reports indicate that populations increased rapidly once established. Observationally, however, it is likely that they do not double their population in less than 10 years. Reported in Mississippi to shade out the native herbaceous understory vegetation. Sources of information: Ticknor, R.L. 2004. English holly _ Ilex aquifolium, a jewel or a menace in the Pacific Northwest? The Nature Conservancy website.; DiTomaso, J.M. - observational
Question 2.3 Recent trend in total area infested within state? Assess the overall trend in the total area infested by this species statewide. Include current management efforts in this assessment and note them. Select the one letter below that best describes the current trend: A. Increasing rapidly (doubling in total range statewide in <10 years) B. Increasing, but less rapidly C. Stable D. Declining U. Unknown	B Other Published Material
Describe trend: Probably expanding its range, but not at a rapid rate. Expect to expand further. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press); DiTomaso, J.M. - observational
Question 2.4 Innate reproductive potential? Assess the innate reproductive potential of this species. Worksheet A is provided for computing the score.	C Other Published Material
Describe key reproductive characteristics: Flowers do not last for 3 months. Most seed do not germinate for 2-3 years after then disperse. Plants grow slowly and natural regeneration is sparse. Female plants usually begin to produce seed at 5-12 years of age. Seed production is highest in trees more than 20 years old. Much of the biology is unknown. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press)
Question 2.5 Potential for human-caused dispersal? Assess whether this species is currently spread: or has high potential to be spread: by direct or indirect human activity. Such activity may enable the species to overcome natural barriers to dispersal that would not be crossed otherwise, or it may simply increase the natural dispersal of the species. Possible mechanisms for dispersal include: - commercial sales for use in agriculture, ornamental horticulture, or aquariums; - use as forage, erosion control, or revegetation; - presence as a contaminant (seeds or propagules) in bulk seed, hay, feed, soil, packing materials, etc.; - spread along transportation corridors such as highways, railroads, trails, or canals; - transport on boats or boat trailers. Select the one letter below that best describes human-caused dispersal and spread: A. High: there are numerous opportunities for dispersal to new areas. B. Moderate: human dispersal occurs, but not at a high level. C. Low: human dispersal is infrequent or inefficient. D. Does not occur. U. Unknown.	A Other Published Material
Identify dispersal mechanisms: Still widely cultivated and distributed. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press)
Question 2.6 Potential for natural long-distance dispersal? We have chosen 1 km as the threshold of "long-distance." Assess whether this species is frequently spread, or has high potential to be spread, by animals or abiotic mechanisms that can move seed, roots, stems, or other propagules this far. The following are examples of such natural long-distance dispersal mechanisms: - the species' fruit or seed is commonly consumed by birds or other animals that travel long distances; - the species' fruits or seeds are sticky or burred and cling to feathers or hair of animals; - the species has buoyant fruits, seeds, or other propagules that are dispersed by flowing water; - the species has light propagules that promote long-distance wind dispersal; - The species, or parts of it, can detach and disperse seeds as they are blown long distances (e.g., tumbleweed). Select the one letter below that best describes natural long-distance dispersal and spread: A. Frequent long-distance dispersal by animals or abiotic mechanisms. B. Occasional long-distance dispersal by animals or abiotic mechanisms. C. Rare dispersal more than 1 km by animals or abiotic mechanisms. D. No dispersal of more than 1 km by animals or abiotic mechanisms. U. Unknown.	A Reviewed Scientific Publication
Identify dispersal mechanisms: Birds and mammals consume and disperse a proportion of the fuits. In the Pacific Northwest it is spreading at an increasing rate into forests by birds. Most of the seed are removed from the tree by birds. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press);Reichard, S. 1966. Ilex aquifolium. Page 57, In Invasive Plants. Weeds of the Global Garden. Randall, J.M. and J. Marinelli, eds., Brooklyn Botanical Garden, Brooklyn, NY.; Obeso, J.R. and I.C. Fernandez-Calvo. 2003. Fruit removal, pyrene dispersal, post-dispersal predation and seedling establishment of a bird-dispersed tree. Plant Ecology 165(2):223-233.
Question 2.7 Other regions invaded? Assess whether this species has invaded ecological types in other states or countries outside its native range that are analogous to ecological types not yet invaded in your state (see Worksheets B, C, and D for California, Arizona, and Nevada, respectively, in Part IV for lists of ecological types). This information is useful in predicting the likelihood of further spread within your state. Select the one letter below that best describes the species' invasiveness in other states or countries, outside its native range. A. This species has invaded 3 or more ecological types elsewhere that exist in your state and are as yet not invaded by this species (e.g. it has invaded Mediterranean grasslands, savanna, and maquis in southern Europe, which are analogous to California grasslands, savanna, and chaparral, respectively). B. Invades 1 or 2 ecological types that exist but are not yet invaded in your state. C. Invades elsewhere but only in ecological types that it has already invaded in the state. D. Not known as an escape anywhere else. U. Unknown.	C Other Published Material
Identify other regions: Also invasive in Oregon and Washington. Also reported as an invasive problem in Mississippi, where they consider it a serious threat. Native to Europe and western Asia. Appears to occupy similar habitats in the Northwest and in Mississippi. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press); Meyers-Rice, B. and J. Randall. 2004. Weed Report: Ilex spp. Gallberry, Yaupon. The Nature Conservancy Wildland Weeds Management and Research 1998-1999 Weed Survey.
Section 3: Distribution
Question 3.1 Ecological amplitude/Range? Refer to Worksheet C and select the one letter below that indicates the number of different ecological types that this species invades. A. Widespread: the species invades at least three major types or at least six minor types. B. Moderate: the species invades two major types or five minor types. C. Limited: the species invades only one major type and two to four minor types. D. Narrow: the species invades only one minor type. U. Unknown.	B Other Published Material
Has escaped cultivation and become invasive in certain areas of the moist coastal forests in California, Oregon and Washington. In California it is found in coastal forests, and riparian areas of forests and woodlands. First introduced as an ornamental to the US in the 1700. Introduced to the Pacific Northwest in 1869. Sources of information: DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California and Other Western States. Univ. Calif., Ag. Natural Res. (in press); Reichard, S. 1966. Ilex aquifolium. Page 57, In Invasive Plants. Weeds of the Global Garden. Randall, J.M. and J. Marinelli, eds., Brooklyn Botanical Garden, Brooklyn, NY.;Ticknor, R.L. 2004. English holly _ Ilex aquifolium, a jewel or a menace in the Pacific Northwest? The Nature Conservancy website.
Question 3.2 Distribution/Peak frequency? To assess distribution, record the letter that corresponds to the highest percent infested score entered in Worksheet C for any ecological type.	D Observational
Describe distribution: Not widely distributed as an invasive. Mainly in the northwestern part of the state and around the Bay Area, but not common there. Much more common as a cultivated plant. Sources of information: DiTomaso, J.M. - observational

Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less	No
Dense infestations produce >1,000 viable seed per square meter	No
Populations of this species produce seeds every year.	No
Seed production sustained over 3 or more months within a population annually	No
Seeds remain viable in soil for three or more years	Yes
Viable seed produced with both self-pollination and cross-pollination	No
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes	No
Fragments easily and fragments can become established elsewhere	No
Resprouts readily when cut, grazed, or burned	Yes
Total points:	3
Total unknowns:	0
Total score:	C? Scoring Criteria for Worksheet A A. High reproductive potential (6 or more points). B. Moderate reproductive potential (4-5 points). C. Low reproductive potential (3 points or less and less than 3 Unknowns). U. Unknown (3 or fewer points and 3 or more Unknowns).

Related traits:

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)

Major Ecological Types	Minor Ecological Types	Code? A means >50% of type occurrences are invaded; B means 20% to 50%; C means 5% to 20%; D means present but <5%; U means unknown (unable to estimate percentage of occurrences invaded)
Marine Systems	marine systems
Freshwater and Estuarine	lakes, ponds, reservoirs
Aquatic Systems	rivers, streams, canals
Aquatic Systems	estuaries
Dunes	coastal
	desert
	interior
Scrub and Chaparral	coastal bluff scrub
	coastal scrub
	Sonoran desert scrub
	Mojavean desert scrub (incl. Joshua tree woodland)
	Great Basin scrub
	chenopod scrub
	montane dwarf scrub
	Upper Sonoran subshrub scrub
	chaparral
Grasslands, Vernal Pools, Meadows, and other Herb Communities	coastal prairie
	valley and foothill grassland
	Great Basin grassland
	vernal pool
	meadow and seep
	alkali playa
	pebble plain
Bog and Marsh	bog and fen
Bog and Marsh	marsh and swamp
Riparian and Bottomland habitat	riparian forest	D, < 5%
	riparian woodland	D, < 5%
	riparian scrub (incl.desert washes)
Woodland	cismontane woodland
	piñon and juniper woodland
	Sonoran thorn woodland
Forest	broadleaved upland forest
	North Coast coniferous forest	D, < 5%
	closed cone coniferous forest
	lower montane coniferous forest
	upper montane coniferous forest
	subalpine coniferous forest
Alpine Habitats	alpine boulder and rock field
Alpine Habitats	alpine dwarf scrub
	Amplitude (breadth):	B
	Distribution (highest score):	D

Infested Jepson Regions

Click here for a map of Jepson regions

Central West
Great Valley
Northwest
Sierra Nevada
Southwest

California Invasive Plant Council

Protecting California’s environment and economy from invasive plants

Plant Assessment Form

More Ilex aquifolium resources

Ilex aquifolium

Evaluator(s)

List committee members

General Comments

Table 2. Criteria, Section, and Overall Scores

Table 3. Documentation

Worksheet A - Innate reproductive potential

Related traits:

Worksheet C - California Ecological Types

Infested Jepson Regions