November Tree (or Shrub, Rather) of the Month – Invasive Asian Honeysuckle

Honeysuckle HackFest 2024

Two summers ago, my neighbor approached me about planting some arborvitae along the fence-line in the alley between our two garages. Initially, I expressed hesitation because there was already a bush there providing fairly dense privacy and blocking access to my fence, and therefore, my backyard. This was important to me because I have been the victim of at least three garage break-ins. I simply can’t afford to keep replacing my lawnmower over and over. But I admitted I did love arborvitae, and so I looked into this plant providing dense coverage. Lo and behold, it was Asian honeysuckle.

Asian honeysuckle, a group of honeysuckle species including Lonicera maackii, Lonicera japonica, and Lonicera tatarica, is native to regions of East Asia. Known for its fragrant flowers and hardy growth, these species were introduced to the United States in the 1800s as ornamental plants, valued for their fast-growing, attractive vines and ability to provide quick hedgerows. Additionally, they were planted for erosion control and as a natural fence in agricultural landscapes, appreciated for their dense growth and adaptability to different soils. However, over time, the spread of these plants revealed an unintended consequence: they began to outcompete native flora and dominate the ecosystems in which they were introduced.

Asian honeysuckles belong to the Caprifoliaceae family, and their taxonomy within the genus Lonicera places them among a variety of honeysuckles with diverse traits. However, unlike native honeysuckle species, which typically coexist with other plants without disruption, the Asian varieties exhibit aggressive growth patterns. Lonicera maackii, or Amur honeysuckle, for example, can grow up to 20 feet tall with branches that form thick layers, blocking sunlight from reaching the forest floor. This shading effect hampers the growth of native plants, which often cannot compete with the honeysuckle’s rapid expansion. The dense canopies created by these shrubs limit biodiversity, as native plants struggle to survive beneath the honeysuckle’s dense foliage. This reduction in plant diversity has downstream effects on the ecosystem, affecting pollinators and other wildlife that depend on native plants for food and habitat.

The rapid spread of Asian honeysuckle can also be attributed to its prolific seed production. Birds and other animals are attracted to the bright red berries produced by species like Lonicera maackii, which are high in sugars but nutritionally inferior to berries from native plants. As birds consume these berries and disperse the seeds, the honeysuckle finds new areas to colonize, spreading further into native forests, grasslands, and even suburban areas. The seeds are remarkably resilient, able to germinate in a variety of soil types and conditions, making the plant even harder to control.

What makes Asian honeysuckle particularly challenging from an ecological perspective is that it not only competes directly with native plants but also alters the soil chemistry. Studies have shown that some species of Asian honeysuckle release allelopathic chemicals—substances that inhibit the growth of other plants. This further suppresses the growth of native flora, creating a feedback loop where the honeysuckle becomes more dominant, and native species struggle even more to re-establish. This disrupts the balance of ecosystems, reducing habitat quality for native animals and making it difficult for indigenous plants to regenerate naturally.

The invasion of Asian honeysuckle into native ecosystems has prompted numerous control efforts. Methods range from physical removal and cutting to the careful application of herbicides. However, controlling this invasive species is complex and resource-intensive. Without intervention, the spread of Asian honeysuckle is likely to continue altering habitats across North America, reducing biodiversity, and reshaping the landscapes we depend on. In this way, Asian honeysuckle’s introduction highlights the importance of considering ecological impacts when importing non-native species, as well as the intricate balance required to maintain healthy, biodiverse habitats.

And so, armed with this newfound knowledge, I decided to hack that honeysuckle to make way for the arborvitae my neighbor desired. Now, two seasons later, that resistant, stubborn, invasive honeysuckle is still shooting sprouts up from the remnants of the former plant. Seeing firsthand how tough this invasive species is to control has only strengthened my commitment to fighting it back—especially as I learned that I’m not alone in this effort.

During a recent walk at Deer Haven / Havener Park south of Delaware, our resident tree expert Mort Schmidt met Brian Mayer, who is coordinating the first annual Honeysuckle HackFest. Invasive honeysuckle is destroying our understory and ruining native habitat, but it can potentially be beaten back. On Saturday, November 16, volunteers are needed to cut plants, and to assist with logistics. Your efforts will consist of 3-hour shifts between 9:00 a.m. and 6:00 p.m. You can go to https://givepul.se/hm5191 to register.

– Written by Luke Toney with contributions from Mort Schmidt