Invasive Tree Lilac (Syringa reticulata)

tier 5

By Melody Cerniglia

History & Introduction

Lilacs include 30 species of deciduous shrubs and small trees belonging to the Oleaceae, or olive, family. They are native to southeastern Europe and eastern Asia and were introduced in North America. Invasive tree lilac (Syringa reticulata) was discovered in the mountains of Japan. This species was first described in 1875 by the Russian botanist Maximowicz, who named it Syringa amurensis var. japonica. It was introduced in the United States in 1876 at the Arnold Arboretum in Boston. Since then, it has long been used in ornamental plantings in yards and urban areas, as well as a common street tree for many cities, counties, and local municipalities (which is not recommended by LIISMA).

Today, the invasive tree lilac is escaping cultivation in many parts of the country, especially the northeastern US and parts of upstate New York. In the Adirondack and Catskill regions, the species has been reported escaping cultivation and invading natural areas, such as riparian corridors and floodplains, where it can form monocultures that exclude native plants. According to the New York Natural Heritage Program (NYNHP) NYS Tier Ranking list, the species is listed as a Tier 3 species (containment) for the state, and a Tier M (monitor) for the LIISMA region, with consideration in making it a Tier 2 species (early detection and eradication) in the near future.

Identification & Biology

The genus (Syringa) is derived from the Greek word “syrinx,” meaning tube or pipe–in reference to the pith-filled (but easily hollowed) stems of some genus plants. The specific epithet (reticulata) refers to the netted-vein appearance of the leaf veins.

The invasive tree lilac is quite larger than its shrubby relatives, growing from 15 to 40 feet tall and about 20 feet wide, with an oval, rounded canopy. The species may be single or multi-stemmed, thus categorizing it as a small tree or large shrub. The species is deciduous. Leaves are simple, opposite facing, acuminate, and ovate/orbicular to cordate with smooth margins, a rounded base, and slightly downy undersides. The leaves are a matte dark green color on the front of the leaf, with a slightly duller matte green underside. Reddish brown, peeling bark is observed on younger branches, turning closer to gray in the plant’s maturity. The bark is mostly smooth with raised blisters and lenticels.

This plant produces showy, creamy white inflorescences born in large, upright, terminal panicles that can grow up to 12 inches long. These are most notably emerging in late spring to early summer, which is considered late for most lilac species. The inflorescences give way to “open banana peel” shaped clusters of brown capsules that persist into winter.

The invasive tree lilac and common lilac (Syringa vulgaris) are close relatives, but differing species. They somewhat resemble each other in leaf shape and arrangement; both have the potential to be multi-stemmed and possess showy clusters of flowers. These species differ in that the invasive tree lilac has a more tree-like habit and can grow to 30 feet tall, and in rare cases, taller. In comparison, common lilacs tend to stay below 10 feet in height.

The tiny, four-petaled flowers that make up the large inflorescence in common lilacs are usually a pinkish/violet color, but sometimes can be white. The (also tiny) flowers that make up the (larger) inflorescences of invasive tree lilacs have smaller petals than the common lilac and are always white or cream-colored.

Subspecies:

Syringa reticulata subsp. reticulata is native to Japan and is sometimes commonly called Japanese tree lilac. Syringa reticulata subsp. pekinensis is native to China and is sometimes commonly called Chinese tree lilac or Peking lilac. Syringa reticulata subsp. amurensis is native to Korea and eastern Russia and is commonly called Amur tree lilac or Amur lilac.

Damage & Concern

Invasive tree lilac tolerates a range of site conditions. A popular ornamental, this species is frequently found in yards or urban areas. It can escape cultivation, invading and dominating natural areas such as riparian corridors and floodplains. It is known to form monocultures that can shade out native understory plants and compete with native tree species. It also produces a large seed bank that could threaten biodiversity and ecological sustainability.

Experts in the Midwest consider the tree a plant of concern, and some gardens in the region have reported it spreading from cultivation. Escaped populations of the tree have been detected in several North American states, including Vermont, Minnesota, and Pennsylvania. It was also reported that the tree was the most common tree species in multiple forested sites according to a University of Pittsburgh study, which could indicate a negative impact on local ecological communities.

Management & Control

Early detection and prevention:

Early Detection and Rapid Response (EDRR) is a crucial part of managing invasive species because management is more likely to be successful when implemented early. EDRR is a coordinated set of actions to find and eradicate invasive species before they can spread and cause harm. It can reduce the long-term costs, economic burden, and ecological harm that invasive species can have on communities.

Assist LIISMA’s Early Detection and Rapid Response efforts by reporting any newly emerging infestations of invasive tree lilac on Long Island to iMapInvasives or iNaturalist.

Manual and mechanical control:

Small saplings can be hand-pulled or dug out. Larger trees can be more difficult to manage, but you can try using a shovel, spade, truck, or tractor.

Chemical control:

You can use systemic herbicides such as glyphosate or triclopyr on larger lilac trees by applying them to the cut stem, basal bark, or with a hack and squirt method. You can also spray lilac runners with a “sucker stopper” herbicide, which typically contains the active ingredient, Ethyl 1-naphthaleneacetate. Always follow the herbicide label and federal, state, and local regulations when selecting and applying herbicide.

Monitoring & Reporting

LIISMA is monitoring invasive tree lilac as part of our Early Detection and Rapid Response program. As reports of the species are collected, LIISMA works with partners and landowners to delineate and manage early emerging infestations of the species before they become widespread. Invasive tree lilac is currently a Tier M species on Long Island, prioritized for monitoring, with the potential of it becoming a Tier 2 species (early detection and eradication) in the foreseeable future.

Your reports matter to us–report the species to iMapinvasives or iNaturalist as soon as you detect it!

iNaturalist is an app and website that can help you record your own observations, identify species, collaborate with others, and access the observational data collected by iNaturalist users. Already using iNaturalist? Join a LIISMA iNaturalist Project to have your invasive species observations automatically uploaded to our projects! Here are some of our projects you can join: Invasive Species in Priority Areas, EDRR Species, LIFERS, Tier 1 Invasive Species, and more!