Plant Assessment Form

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 commitee 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 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? 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?
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? 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? 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?
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? 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? 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? 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? 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? 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? 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? 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? 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?

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?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirs
Aquatic Systemsrivers, streams, canals
estuaries
Dunescoastal
desert
interior
Scrub and Chaparralcoastal 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 Communitiescoastal prairie
valley and foothill grassland
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forestD, < 5%
riparian woodlandD, < 5%
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forestD, < 5%
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
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