Japanese honeysuckle

Japanese honeysuckle (Lonicera japonica)

COMMON NAMES:
Japanese honeysuckle

SCIENTIFIC SYNONYMS:
Lonicera japonica Thunb. var. aureo-reticulata (T. Moore) G.

Nicholson
Lonicera japonica Thunb. var. chinensis (P.W. Watson) Baker
Nintooa japonica (Thunb.) Sweet

CONFIRMATION STATUS: Confirmed.

TAXONOMY: The currently accepted name for Japanese honey-

suckle is Lonicera japonica Thunb.

NATIVE STATUS: Introduced, United States and Canada.

GENERAL BOTANICAL CHARACTERISTICS: Japanese honey-

suckle is a nonnative, woody, trailing or twining, perennial vine. Stems

are often 0.4 to 2 inches (1-5 cm) in diameter, reaching 4 inches (10 cm)

on older plants, and can grow to 18 feet (5.5 m) or more in length. Bark

is corky and shredded on older stems, peeling readily. Rooting depth is

generally 6 to 12 inches (15-30 cm) on moist sites, and up to 40 inches

(102 cm) on dry sites. Roots may extend laterally to 8.5 feet (2.5 meters)

from the root crown. Leaves of Japanese honeysuckle are 1 to 4.8 inches

(2.5-12 cm) long by 0.6 to 2.4 inches (1.5-6.0 cm) wide. Japanese honey-

suckle is generally evergreen in the southern parts of its eastern North

American range (Maryland southward), becoming increasingly deciduous

to the north. The deciduous/evergreen nature of Japanese honeysuckle in

the western United States is not clear. It has been characterized as "half

evergreen" in California. Flowers of Japanese honeysuckle are in axillary

pairs with corollas 0.6 to 2 inches (1.5-5 cm) long. Fruits are sessile berries,

0.16 to 0.24 inch (4-6 mm) in diameter, with 2-5 seeds per fruit.

REGENERATION PROCESS: Japanese honeysuckle is pollinated by
insects and hummingbirds. Research in Japan indicates flowers often do
not open until dusk, probably as a strategy to conserve pollen for nocturnal
hawkmoths. Hawkmoths consume only nectar and are more efficient pollin-
ators than bees, which consume both nectar and pollen. Sexual reproduc-
tion of Japanese honeysuckle may be pollinator-limited along the western
edge of its range in eastern North America; fertile fruit production has
been found to range from 0% to 36% in Arkansas and Oklahoma in natural-
ly pollinated populations.

Flowering and seed production are most prolific, and occur at an earlier age,
when plants are in open habitats. In eastern Texas, Japanese honeysuckle
bore fruit at age 3 when plants were open-grown and at age 5 when shade-
grown. In general, fruit production peaked when plants were 4 to 6 years
old and declined considerably thereafter.

Japanese honeysuckle seeds are frequently dispersed by frugivorous birds
and small mammals. Bird dispersal is typically by species that frequent
brushy areas, thickets, and forest openings. Birds that frequent forest open-
ings, for example, usually fly from 1 opening to another, depositing seeds

at each roosting site. This means of seed dispersal generally ensures de-

position in a habitat where the seedling has a high probability of success,

such as beneath a sapling tree suitable for stem twining.

Seedling establishment and growth are slow during the initial years of
development in new populations. Seedlings are susceptible to drought
and shading. Establishment is limited by competition for moisture with
prairie grasses and forbs at the western limits of Japanese honeysuckle's
distribution in eastern North America. Because seeds are small and contain
limited stored carbohydrates, seedlings must begin photosynthesis soon
after germination. For this reason, seedling establishment may be limited
in areas such as dense grasslands, where ground-level light competition is
intense and there are no structures for young honeysuckle stems to climb.

Once established, Japanese honeysuckle colonies can spread rapidly. Stems
growing along the ground provide structure for new twining stems so that,
even in the absence of other supporting vegetation, Japanese honeysuckle
can form dense mats of monospecific vegetation up to 5 feet (1.5 m) deep.
Single plants may produce 30 feet (9 m) of stem per year. Twining vines
have been reported up to 49 feet (15 m) above the ground in New Zealand.
Japanese honeysuckle vines are unable to climb tree boles > 4 inches (10
cm) in diameter without the aid of trellises provided by bole-climbing vines
such as grape (Vitis spp.).

Japanese honeysuckle sprouts from the root crown and layers. Adventi-
tious roots can occur at the nodes of trailing stems, or in response to stem
cambium damage.

SITE CHARACTERISTICS: Japanese honeysuckle occurs on a variety
of sites within its North American range. It is most common locally in areas
where it was previously planted for hedges, erosion control, wildlife habitat,
or ornamental purposes.

Disturbance is an important site characteristic promoting the establishment
and success of Japanese honeysuckle. It is capable of invading "openings"
within a variety of sites in eastern North America, either by seedling germ-

ination or vegetative spread. Japanese honeysuckle is most prolific at forest
edges and in open areas, but can persist under a closed forest canopy. It
often invades forests where there is moderate disturbance of vertical
structure, allowing more light into the understory. Overstory removal is
not a necessary precondition for invasion, although Japanese honeysuckle
biomass production is greatest where "vertical-structure disturbance" is
greatest.

Japanese honeysuckle occurs on a variety of soil types, but is "noticeably
absent" on coarse sands and poor peat soils. Distribution may be limited
on xeric sites with coarse, well-drained, infertile soils on the southeastern
coastal plain. It is likely that extensive areas of poorly drained soils contrib-
ute to the absence of invasive Japanese honeysuckle in southern Florida.

SUCCESSIONAL STATUS: While Japanese honeysuckle is found with-
in a variety of successional stages in eastern North America, it seems to
occur in the greatest densities in early-successional habitats such as old
fields and shrub thickets. It can be found in, and sometimes dominates,
abandoned agricultural fields in early stages of succession. Japanese honey-
suckle displayed the highest relative cover and greatest frequency of any
plant species 10 years after hurricane-related debris avalanches in the Blue
Ridge Mountains of Virginia. It appears that Japanese honeysuckle benefits
from a combination of available light and small-diameter vertical structure,
conditions commonly found in recently disturbed habitats.

Despite its relative affinity for open habitats, Japanese honeysuckle also has
the ability to spread extensively within mature forest, persisting for many
years in the understory until disturbance creates a gap in the canopy. If pre-
sent at the time of gap formation, it can respond with vigorous growth, poten-
tially dominating understory strata. The ability of Japanese honeysuckle to
establish and persist in later-successional stages of various eastern forests
partly depends upon its ability to tolerate shade. Japanese honeysuckle can
reportedly survive substantial periods of "extreme shade," although growth
is substantially reduced.

Dense concentrations of Japanese honeysuckle can inhibit regeneration of
woody forest species. This may lead to a "disturbance climax" where suc-
cession is altered and the community is maintained as a virtual Japanese
honeysuckle monoculture. Forest management activities that remove part
or all of the overstory can enhance opportunities for Japanese honeysuckle,
frequently at the expense of desirable native and/or commercial species.
For example, Japanese honeysuckle production in southeastern forests is
frequently stimulated by silvicultural thinning in mixed pine/hardwood
stands.

SEASONAL DEVELOPMENT: Japanese honeysuckle often retains its

leaves into winter, with abscission sometimes occurring after new leaves
have fully developed in spring. The timing of abscission is probably relat-

ed to climate and occurs earlier in the year in northern parts of its range.

For example, leaves are retained through late March in the South Carolina
coastal plain, but only until late December or January in Delaware. In
southern California leaves are shed in fall, or generally in response to
drought. New leaves form by mid-March in Maryland. Germination
occurs between early March and late April in eastern Tennessee.

GENERAL DISTRIBUTION: Japanese honeysuckle is native to east-
ern Asia. It was introduced to North America in the early 1800s. Self-sus-
taining populations have subsequently established in southern New Eng-

land and the Ohio Valley south to the Atlantic and Gulf coastal plains and

west to the Mississippi Valley and Ozark Mountains of Missouri and

Arkansas. Japanese honeysuckle is widely planted across much of North

America and frequently escapes cultivation. However, it not usually inva-

sive in areas outside the region described above. It can be found from

Maine to Florida and from Michigan and Wisconsin south to Nebraska,

Kansas, Oklahoma, and Texas. It is not reported from New Hampshire.

It also is reported in southern Ontario, Hawaii, and Puerto Rico, and as an occasional escapee in the southwestern United States.

SKY MEADOWS DISTRIBUTION:

Vine specimens can be found on trails marked in red.

       Bleak House
       Appalachian Trail/Old Trail
       South Ridge/North Ridge
       Gap Run
       Snowden
       Woodpecker Lane

       Sherman's Mill
       Rolling Meadows/ Lost Mountain
     Fish Pond

The specific distribution of Japanese honeysuckle has not been determined;

in some areas (e.g., Sherman's Mill trail), it has been observed growing pro-

fusely.

HABITAT TYPES AND PLANT COMMUNITIES: Japanese honey-
suckle occurs in a variety of habitat types and plant communities through-
out North American. It may be found within most plant associations of the
southern and east-central United States. It occurs in oak (Quercus spp.)-
pine (Pinus spp.) associations, northern white-cedar (Thuja occidentalis)
stands, white (Pinus strobus), red (Pinus resinosa), pitch pine (Pinus
rigida) stands, and mixed hardwood stands. It is rare in spruce Picea spp.)
and fir (Abies spp.) forest types and coastal pine barrens. Plant associations
for Japanese honeysuckle in the more arid western United States are less
clear.

IMPORTANCE AND USES: Japanese honeysuckle is an important
browse species for white-tailed deer throughout much of the eastern and
southern United States, especially during poor mast years and in winter
when other food sources are scarce or inaccessible. It is particularly impor-
tant for white-tailed deer in the South. Japanese honeysuckle is considered
a "choice" woody browse species for white-tailed deer on the Oconee

National Forest in the Georgia Piedmont. In areas of northern Alabama

managed primarily for loblolly pine production, Japanese honeysuckle

constituted 49.4% of the year-round diet of white-tailed deer. No other

single food item amounted to >6%. Cultivation and fertilization of Japa-

nese honeysuckle food plots may provide winter forage for white-tailed

deer in the southeastern United States, although such practices have been discouraged.

In eastern forests, wild turkeys, northern bobwhite, and various songbirds
utilize Japanese honeysuckle as food, particularly during winter when other
food may be scarce. Its persistent leaves shield fruit from sleet when other
food is glazed with ice. Wood thrushes, hermit thrushes, tufted titmice,
dark-eyed juncos, eastern bluebirds, purple finches, pine grosbeaks, Ameri-
can robins, white-throated sparrows, and yellow-rumped warblers consume
fruits. Japanese honeysuckle also provides excellent forage for rabbits.
Ruby-throated hummingbirds feed from the flowers.

Japanese honeysuckle thickets provide cover for eastern cottontails, north-
ern bobwhite, wild turkeys, and songbirds. Northern bobwhite nest in
Japanese honeysuckle thickets in southern Illinois. Japanese honeysuckle
thickets may provide bedding cover for white-tailed deer, and good habitat
for cotton rats.

Japanese honeysuckle was promoted for many years as a horticulture plant,
and is still sold for this purpose in many areas. It has been used as a fast-
growing plant for rehabilitation of disturbed, erodible ground. Several con-
stituents of Japanese honeysuckle have shown anti-inflammatory activity
comparable to aspirin.

While Japanese honeysuckle was promoted and planted as a beneficial wild-
life species in the eastern United States during the mid 1900s, emphasis
has now changed toward controlling its spread. Japanese honeysuckle does
provide food for wildlife, but it also suppresses many native plants that may
be of greater economic or ecological value. Japanese honeysuckle directly
impacts native plants through competition for light and soil resources. Twin-
ing vines grow up and past small-diameter trees and shrubs, blocking sun-
light with their dense canopy and eventually pulling down their dead hosts
with the weight of the vine. Twining Japanese honeysuckle vines may in-
crease stem:leaf ratios of host plants, presumably because the extra weight
exerted on the host plant requires greater stem support than would other-
wise be required.

Japanese honeysuckle may also impact native communities by altering for-

est structure and species composition. Invasion of Japanese honeysuckle in

east- ern forests can lead to suppressed reproduction of herbs and woody

plants. Although the ground layer is most suppressed, plants of nearly all

forest strata begin growth at the ground layer and are hence subject to sup-

pression. Presence of Japanese honeysuckle and its effects upon understory

regeneration could promote dramatic changes in forest structure. American
elm (Ulmus americana), black cherry, and yellow-poplar on a Potomac
River island in Washington D.C. were particularly susceptible to suppressed
regeneration due to shading from Japanese honeysuckle. Japanese honey-
suckle constrains oak regeneration in southeastern hardwood bottoms,
especially following overstory thinning or removal. It can also substantially
inhibit pine regeneration in harvested stands when it is present prior to har-
vest. Presence of Japanese honeysuckle vines in harvestable stands may
require substantial expense and effort to ensure pine regeneration.

Japanese honeysuckle retains photosynthetically active foliage during
winter throughout much of its range. This trait, combined with ability to
produce new leaves in early spring, enhances its competitive ability, and
hence, its invasiveness. In many areas, Japanese honeysuckle can produce
as much as 2 months of growth before most deciduous associates begin to
grow. For example, in Maryland Japanese honeysuckle usually leafs out by
mid-March, while the native oak forests are generally leafless until May.
However, Japanese honeysuckle becomes less invasive in northern por-
tions of its eastern North American range due to a shorter growing season
and frequent winter kill of accumulated stem growth. In the arid western
United States, Japanese honeysuckle is not likely to become widely inva-
sive due to drought intolerance, especially of seedlings. However, it may
persist in irrigated or riparian areas, becoming a localized pest.