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Privet A privet is a flowering plant in the genus ''Ligustrum''. The genus contains about 50 species of erect, deciduous or evergreen shrubs, sometimes forming small or medium-sized trees, native to Europe, north Africa, Asia, many introduced and nat ...
s are any of a number of shrubs or
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
s in the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
''Ligustrum'', many of which are invasive. The genus contains about 50
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
native to the
Old World The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by th ...
and
Australasia Australasia is a region that comprises Australia, New Zealand and some neighbouring islands in the Pacific Ocean. The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecolo ...
. Many members of the genus are grown as
ornamental plants Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...
in parts of the world. Several species of privet have become a nuisance in regions outside their ranges. In these conditions they are most commonly found wherever there is disturbed soil, soil that is physically perturbed from its natural state through fire or mechanical machinery, such as along fencerows, old fields, ditches, and forest margins.Maddox, V., J. Byrd, Serviss, B. (2010). Identification and Control of Invasive Privets (''Ligustrum'' spp.) in the Middle Southern United States. ''Invasive Plant Science and Management''. 3:482-488. Privet grows particularly well in
riparian forests A riparian forest or riparian woodland is a forested or wooded area of land adjacent to a body of water such as a river, stream, pond, lake, marshland, estuary, canal, sink or reservoir. Etymology The term riparian comes from the Latin word ...
, which are found throughout the
Southeastern United States The Southeastern United States, also referred to as the American Southeast or simply the Southeast, is a geographical region of the United States. It is located broadly on the eastern portion of the southern United States and the southern po ...
.Hanula, J.L, Horn, S., Taylor, J.W. (2009). Chinese privet (''Ligustrum sinense'') Removal and its Effect on Native Plant Communities of Riparian Forests. ''Invasive Plant Science and Management'' 2:292-300. Although tolerant of varying soil and light conditions, including a tolerance for shade, privet survives best in mesic soil with abundant sunlight.Urbatch, L. Chinese Privet: Plant Guide. ''USDA and NRCS''.Retrieved 19 April 2022


Economic and cultural effects

Privet is considered a huge problem in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...
and the east coast of Australia (''
Ligustrum lucidum ''Ligustrum lucidum'', the broad-leaf privet,Weed profile: Privet
New So ...
'', ''
Ligustrum sinense ''Ligustrum sinense'' (Chinese privet; syn. ''L. villosum''; in Mandarin: 杻; pinyin: chǒu) is a species of privet native to China, Taiwan and Vietnam,Flora of China''Ligustrum sinense''/ref> and naturalized in Réunion, the Andaman Islands, N ...
'' and ''
Ligustrum vulgare ''Ligustrum vulgare'' (wild privet, also sometimes known as common privet or European privet) is a species of '' Ligustrum'' native to central and southern Europe, north Africa and southwestern Asia, from Ireland and southwestern Sweden south to ...
''). It is banned from sale or cultivation in New Zealand because its pollen is known to cause
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, c ...
and eczema in sufferers. Privet can be removed by contacting local government agencies to report its presence. but in Auckland it is only a surveillance pest plant in the 2012 Regional Pest Management Strategy. The NZ Weedbusters site provides guidance on how to get rid of the plant. When privet is invasive species, the cost of controlling and removing privet is economically detrimental, something that is problematic for conservation efforts. The annual cost of removing Chinese privet in the United States is estimated to be $737 per acre when a mulching machine and two-person herbicide application crew are employed.Environmental Assessment: Zebra Project (Timber Scale). (2010) ''USDA''. Retrieved 15 March 2013 The cost for foliar glyphosate applications on privet is approximately $130 per acre for chemical and surfactant treatments.


Invasiveness

Privet is a successful invasive species because of its ability to outcompete and therefore displace native vegetation. This competitive superiority to native vegetation is connected with the plant's ability to adapt to different light conditions.Lornalkfosko[ris, Jeffrey L. Walck, Hidayati, S.N. (2002). Growth and Reproduction of the Invasive Ligustrum sinense and Native Forestiera ligustrina (''Oleaceae''): Implications for the Invasion and Persistence of a Nonnative Shrub. ''International Journal of Plant Sciences''. 163: 1001-1010. For example, in low light environments, privet is able to produce fewer and larger ramets than its competitors. These larger ramets make privet more tree-like, making privet better able to compete for light than its more shrub-like native counterparts. Privet is an ideal invasive species because it reproduces both sexually and asexually. Through sexual reproduction, privet produces
seeds A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, includ ...
that are easily dispersed by wind and animals. These seeds can rapidly colonize disturbed soil such as that perturbed by fires, forest clearings, erosion, or abandoned agricultural land. Privet matures quickly, which allows for a short generation cycle and even greater dispersal. The roots of privet can reproduce asexually through root suckers. This
vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spe ...
makes privet difficult and costly to control because root fragments left in the soil can sprout and grow new plants. One reason why privet is so invasive in the United States is because it has few native shrub competitors.Greene, B.T., Blossey, B. (2011). Lost in the weeds: ''Ligustrum sinense'' reduces native plant growth and survival. ''Biological Invasions''. 14:139-150 In a sense, privet is invading and exploiting an open niche within the southern U.S.
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
ecosystem. Prior to privet invasion much of the native land was clear and open; currently, privet forms a dense thicket which chokes out other, usually native, plant life. Thus, privet is believed to be phylogenetically distinct compared to its native cousins.


Ecological impact in the U.S.


Introduction

All nine species of privet currently in the southeast U.S. are
invasive Invasive may refer to: *Invasive (medical) procedure *Invasive species *Invasive observation, especially in reference to surveillance *Invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer ...
. The first species of privet was introduced into the United States in the 1700s as an ornamental plant used as a hedge or foliage for gardens. Glossy privet arrived in the U.S. in 1794, Chinese privet in 1825, Japanese privet in 1845, California privet in 1847, and Amur privet in 1860. Privets escaped cultivation in the early 1900s, but became widely
naturalized Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the i ...
during the 1950s-1970s or later. Currently privet is designated as a foreign invasive plant in Alabama and Georgia and considered a severe threat in North Carolina and Florida. It is estimated that Chinese privet alone occupies over one million
hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100- metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre is ...
s of land across 12 states ranging from Virginia to Florida and west to Texas. The full ecological effect of privet is still being studied. However, data suggest that forests containing large amounts of privet tend to have fewer trees, less shrub diversity, and decreased density of herbaceous plants.Zhang, Y., Hanula, J., Horn, S., Braman, S.K., Sun, J. (2011). Biology of ‘'Leptoypha hospita'’ (''Hemiptera'': ''Tingidae''), a Potential Biological Control Agent of Chinese Privet. ''Ann. Entomol. Soc. Am''. 104: 1327-1333. When introduced to an ecosystem, privet grows quickly and, given time, will produce a thick layer under the forest canopy preventing sunlight from reaching the native plants below. In some cases, this can drive native populations to
extinction Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...
. If left unchecked, privet may result in large-scale ecosystem modification and an overall loss of native species diversity and richness. The Sierra Chicas of Cordoba have experienced just such a widespread landscape change since 1970. In a study by Greene and Blossey using field observations and a transplant experiment, a significant negative correlation was found between percent Chinese privet cover and
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition ...
cover,
species richness Species richness is the number of different species represented in an ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative ab ...
, and plant height. In a comparison of two experimental gardens, each with four native plant species, the plot with Chinese privet contained almost entirely nonnative plants after 64 weeks. Out of approximately twenty plants per species, only single individuals of '' Acer negundo'', ''
Chamaenerion latifolium ''Chamaenerion latifolium'' (formerly ''Epilobium latifolium'', also called ''Chamerion latifolium'') is a species of flowering plant in the evening primrose family known by the English common names dwarf fireweed and river beauty willowherb. I ...
'' and ''C. tribuloides'' survived the entire study when in the presence of Chinese privet. Surviving plants had lower leaf counts and stunted height relative to their counterparts in privet-absent plots. None of the ''Boehmeria cylindrica'' survived. Insects are greatly affected by the proliferation of invasive species such as privet.Hanula, J. L., Horn, S. (2011). Removing an invasive shrub (Chinese privet) increases native bee diversity and abundance in riparian forests of the southeastern United States. ''Insect Conservation and Diversity'' 4: 275-283. For example, one study found the abundance and diversity of butterflies increased following privet removal to almost the same abundance as that of a similar forest community, with no history of privet invasion. In a study conducted in Georgia, privet was found to decrease the diversity of native honeybee colonies. Plots removed of privet resulted in four times as many bee species as control plots in which privet was not removed. Traps placed in undisturbed forest plots with no history of privet caught an average of 210 bees from 34 species, while traps placed in privet-infested plots caught an average of 35 bees from only 9 species. Another example of how privet can have a negative ecological impact in ecological communities is its ability to threaten endangered species.Zhang, Y., Hanula, J., Horn, S., Braman, S.K. and J. Sun. 2011. Biology of Leptoypha hospita (Hemiptera: Tingidae), a Potential Biological Control Agent of Chinese Privet. Ann. Entomol. Soc. Am. 104: 1327-1333. For example, privet threatens the Miccosukee gooseberry, a native plant species that privet is similar to, by encroaching on the gooseberry's habitat and slowly displacing it.Langeland, K. A., Burks, K.C. (1998). Identification and biology of non-native plants in Florida's natural areas. University of Florida, Gainesville. 165 pp. Biological species invasion is considered a main component of global ecosystem change due to changes in
biogeochemical cycle A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and ...
s and
disturbance regimes In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abioti ...
.Gavier-Pizarro, G.I., T. Kuemmerle, L.E. Hoyos, S.I. Stewart, C.D. Huebner, N.S. Keuler, and Radeloff, V.C. (2012). Monitoring the invasion of an exotic tree (Ligustrum lucidum) from 1983 to 2006 with landsat TM/ETM + satellite data and support vector machines in Córdoba, Argentina. ''Remote Sensing of Environment'' 122: 134-145. Invasive species such as privet are known to alter the dominant vegetation type, soil properties, animal behavior, and the natural cycling of resources. For example, Chinese privet increases the decomposition rate of
leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...
by 2.6-fold in riparian forests.Mitchell, J. D., Lockaby, B.G., Brantley, B.F. (2011). Influence of Chinese Privet (Ligustrum sinense) on Decomposition and Nutrient Availability in Riparian Forests. ''Invasive Plant Science and Management'' 4:437-447. However, because the usual method employed to study the impact of privet is to compare invaded and non-invaded areas, available data may be inaccurate. This is because these types of comparison studies have trouble controlling for abiotic and
biotic Biotics describe living or once living components of a community; for example organisms, such as animals and plants. Biotic may refer to: *Life, the condition of living organisms *Biology, the study of life * Biotic material, which is derived from ...
habitat conditions that could be negatively affecting native plant growth.


Effect of climate change

Evidence suggests that
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
s, brought about by increased CO2 concentrations, will increase the spread and proliferation of privet.Bradley, B.A., Wilcove, D.S., Oppenheimer, M. (2010). Climate change increases risk of plant invasion in the eastern United States. ''Biological Invasions'' 12:1855–187 Climate change is predicted to increase competition between native and invasive plants. Additionally, the increased temperatures that result from climate change are predicted to expand the range of plants typically restricted to the deep south where it is warm and moist. In a projection based on the current and predicted CO2 levels, temperature, and precipitation, it was predicted that by the year 2100 privet will have spread as far north as Maine, sweeping across the mid-western United States into Nebraska. Thus, states that are currently free from privet invasion (
Michigan Michigan () is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the List of U.S. states and ...
,
Ohio Ohio () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Of the List of states and territories of the United States, fifty U.S. states, it is the List of U.S. states and territories by area, 34th-l ...
,
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th ...
,
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Roc ...
,
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virgini ...
,
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...
,
Pennsylvania Pennsylvania (; (Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Ma ...
, etc.) are all predicted to become invaded with privet within the next 100 years unless either privet is contained or conservation efforts decrease the effect of pollution on climate change.


Control and removal methods


Methods of control

The same qualities that allow privet to outcompete native species make it extremely difficult to control and eradicate. Privet is manageable with mowing or cutting consistently, as closely to the ground as possible.Chinese Privet. (2013). ''Center for Aquatic and Invasive Plants''. Retrieved 15 March 2013> This will prevent the spread of the privet but will not eradicate it. Even methods such as
controlled burn A controlled or prescribed burn, also known as hazard reduction burning, backfire, swailing, or a burn-off, is a fire set intentionally for purposes of forest management, farming, prairie restoration or greenhouse gas abatement. A contro ...
ing have proven ineffective and actually aid privet growth because privet recovers better than native plants from controlled burns. Mechanical removal of privet, especially for younger plants or smaller areas of growth, can be effective; however, all of the root must be removed to prevent root re-sprouting. Mechanical removal can prove difficult for more large-scale invasions. When such large invasions occur in the natural environment, herbicide use is usually avoided due to the negative impacts on native plants. Thus, the use of many workers or heavy machinery such as bulldozers is the most effective option. However, the soil disturbance and resulting erosion are important considerations when using such measures. When herbicide use is warranted, several methods have proven effective. In all cases, soil disturbance following herbicide treatment is inadvisable. This is due to privet's preference for disturbed soils and its increased ability to compete in such an environment. The length of time that the soil must be left undisturbed varies with the treatment. Foliar applications of
glyphosate Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...
, cut-stump applications of glyphosate or
triclopyr Triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) is an organic compound in the pyridine group that is used as a systemic foliar herbicide and fungicide. Uses Triclopyr is used to control broadleaf weeds while leaving grasses and conife ...
, and basal bark treatments for stems less than 0.5 inches is effective. The foliar treatments are most effective against dense thickets of privet. The best time for such treatments are in late fall and early spring when many of the native species are dormant. Care must be used with such an application to avoid spraying non-target plants. This treatment is generally considered to be less effective than the cut-stump and basal bark methods. The cut-stump method is most useful when treating single plants. This method consists of thoroughly covering the stump of a recently cut plant with herbicides, such as glyphosate and triclopyr. The effectiveness of this treatment is increased by cutting a hole into the surface of the stump. Use of this treatment when the plant breaks the dormant stage as well as when the ground is frozen is advised against as it greatly reduces effectiveness. The basal bark treatment consists of application of herbicide to all basal parts of the plant below 12-15 inches. The bark must be thoroughly wet with herbicide for this treatment to be most effective. The USDA suggests that 25% triclopyr and 75% horticultural oil is the most effective herbicide composition for basal bark treatments. The first known
biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically als ...
of privet is the privet lace bug (
Leptoypha hospita ''Leptoypha'' is a genus of lace bug, lace bugs in the family Tingidae. There are about 17 described species in ''Leptoypha''. Species These 17 species belong to the genus ''Leptoypha'': References Further reading

* * * * * ...
), which has been deployed in New Zealand.


Agencies working to control privet

The Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW) engages with public and private organizations in the effort to combat noxious and exotic weeds, including Chinese and European privet.Federal Interagency Committee for the Management of Noxious and Exotic Weeds Retrieved 15 March 2013 Privet is monitored by the
US Forest Service The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency inc ...
's Invasive Species Program while the
National Park Service The National Park Service (NPS) is an List of federal agencies in the United States, agency of the Federal government of the United States, United States federal government within the United States Department of the Interior, U.S. Department of ...
deploys Exotic Plant Management Teams.National Park Service. Retrieved 15 March 2013 Each team has jurisdiction over ten national parks and works with local volunteers, contractors, and service organizations. These agencies work to eliminate, contain, and/or remove privet because many areas invaded by privet, such as the Piedmont floodplains, are important areas of biodiversity, carbon storage, and resource production.


See also

*
Invasive species in the United States Invasive species are a significant threat to many native habitats and species of the United States and a significant cost to agriculture, forestry, and recreation. The term "invasive species" can refer to introduced/naturalized species, feral sp ...
* Environmental issues in the United States


References

{{wikispecies, Ligustrum Ligustrum Invasive plants Flora invasive in North America