It’s a blaze of red in the autumn, thin branches with tiny leaves aflame. Despite being covered in thorns, red barberry (Berberis thunbergii) likely won over the hearts of homeowners with its colorful fall display. But today this woody plant can be seen far from yards, flanking woodland streams, harboring ticks, and spreading in the Pine Barrens of Long Island, now prohibited from sale in New York State. Understanding how we can prevent the impacts of the “next” barberry and other woody invasive species is a mission horticulturalists, landscapers, and ecologists can take on together.
Barberry did not get up and spread itself to North America on its own. Rather, very often these woody invasive species had a human mediator that helped the plants cross oceans, facilitated their reproduction, showed off their best features, and distributed them widely, in order to make a profit and populate gardens with exciting new species.
For example, in 1862, avid plant collector Thomas Hogg sent numerous Japanese plants to North America during his time as a U.S. Marshall in Japan, including itadori knotweed (Reynoutria japonica), miscanthus (Miscanthus sinensis), vine honeysuckle (Lonicera japonica), bittersweet (Celastrus orbiculatus), porcelain berry (Ampelopsis brevipedunculata) and kudzu (Pueraria montana) – today known to be invasive species in New York. Samuel Browne Parsons of Flushing, Queens, planted and propagated many of these plants for sale at his Kissena Nurseries, facilitating their movement around the region (Del Tredici 2017). We know how the rest of the story goes: introduction, establishment, invasion, panic! – but is it always that simple?
Presumably there were many plants propagated by Parsons that were introduced from other countries but never became “invasive” species. Many non-native species, including some cultivated by Parsons, are enjoyed today for their beauty and style– peegee hydrangea (Hydrangea paniculata var. grandiflora) and zelkova (Zelkova serrata) being two examples. Non-native horticultural species may be prized generally for their resistance to diseases, pests, and deer herbivory. All of these features make a great woody plant for the discerning landscaper.
Invasive species are set apart by being non-native species that also pose harm to the economy, environment, or human health. While most species that are introduced to a new location do not become invasive, the issue really lies with the ones that do. A study from 2024 estimated that invasion rates average 17-25% globally, meaning that in some regions, up to 25% of established, non-native species eventually become invasive (Pfadenhauer & Bradley 2024).
You might ask yourself, how do species “eventually” become invasive? Scientists have long documented a lag phase with invasive species: the period of time between a species’ introduction and explosion in population. One study from New Zealand found that over 90% of 142 invasive plant species had a statistically significant lag phase, and 5% of these species were present for more than 40 years before becoming invasive (Coutts et al. 2017). As our summers and winters get warmer, we expect to also start seeing the emergence of “sleeper species”, or those that are not yet invasive because they are limited by current climate conditions, but could become invasive with climate change (Bradley et al. 2018).
So that leaves us a challenge for assessing new non-native woody plants. Which of the bunch will demonstrate that invasive tendency in the future? If there’s a lag phase, how long would we have to wait to see invasiveness? And how would we recognize it if we saw it?
We can learn something by looking back at the non-native plant invasiveness ranking form that helped inform the prohibited species list for New York State. The form asks dozens of questions about the plant of interest, including its escape from cultivation, known suitable habitats, impact on ecosystem processes and community structure, dispersal ability, germination requirements, and more (NYIS.info 2025). Because invasive species are defined by their negative impacts, ecologists, landscapers, and horticulturists can document the impacts we observe and look to existing research from other areas to make sound decisions.
In light of these questions, some woody species emerging on our radar in the Long Island Invasive Species Management Area include wintergreen barberry (Berberis julianae), giant tree lilac (Syringa reticulata), sapphire berry (Symplocos paniculata), fuzzy deutzia (Deutzia scabra), hardy kiwi (Actinidia arguta), and tea viburnum (Viburnum setigerum). Our early detection and rapid response team is on the lookout, following up on reports of these species in natural areas and coordinating their management where applicable.
The overall goal is to move from reactive actions to proactive prevention of new invasive species, to protect the environment, economy, and human health. As woody plants play an important role anchoring our landscapes, giving structure to gardens, and defining ecological communities, it seems like a great place to start.
Citations:
Bradley, B. A., Beaury, E., Fusco, E. J., Laginhas, B., Pasquarella, V. (2018). Preparing for sleeper species. Northeast Regional Invasive Species & Climate Change Management Network. https://doi.org/10.7275/R5F18WXT
Coutts, S. R., Helmstedt, K. J., & Bennett, J. R. (2017). Invasion lags: The stories we tell ourselves and our inability to infer process from pattern. Diversity and Distributions, 24(2), 244–251. doi:10.1111/ddi.12669
Del Tredici, Peter (2017). The Introduction of Japanese Plants Into North America. Botanical Review 83(5):1-38. 10.1007/s12229-017-9184-3
NYIS.info (2025) NY Invasiveness Ranking Forms 2013. https://nyis.info/resources/ny-invasiveness-ranking-forms-2013/
Pfadenhauer, William G., and Bethany A. Bradley (2024) “ Quantifying Vulnerability to Plant Invasion across Global Ecosystems.” Ecological Applications 34(8): e3031. https://doi.org/10.1002/eap.3031
