Our natural landscapes in Maine are diverse and thriving, thanks in large part to a balance between native plants, soil, and wildlife. However, invasive plants threaten this delicate balance, crowding out native species and disrupting ecosystems.
Informed by Landscape Design School Instructor Rebecca Long's course Overused, Often Invasive Plants and Native Alternatives in Your Area, this article explores: what invasive plants are, why they matter, and argues for finding native alternatives that provide a similar aesthetic while helping protect Maine's ecosystems.
What Are Invasive Plants and Why Do They Matter?
Invasive plants, by definition, are non-native species that spread rapidly and disrupt local ecosystems. These plants are introduced—often by human action, whether intentionally or accidentally—to areas where they have not evolved naturally. Their impact can be profound; they outcompete native species, diminish biodiversity, and interfere with the ecosystem's balance. Before we delve into examples of invasive plants in Maine, let's clarify the definitions of terms essential to understanding this topic:
Native Plant: A native plant is a species that has evolved in a particular ecosystem over hundreds or thousands of years, forming integral relationships with the surrounding flora, fauna, and climate.
Non-Native Plant: Non-native plants are introduced with human help to new regions or habitats where they were not previously found. These introductions can occur intentionally, such as through gardening, or accidentally, as seeds hitch rides on vehicles or shoes.
Invasive Plant: Invasive plants are non-native species that establish quickly and spread aggressively, often at the expense of native plants. Their growth and spread can significantly alter or even damage ecosystems.
Opportunistic Native (Aggressive Native): Opportunistic natives, while technically native, can act in a way similar to invasives in disturbed environments. They spread rapidly, often outcompeting other plants on the site.
Understanding these distinctions is essential because not every non-native plant is harmful, and some native plants can become problematic in certain settings.
The Role of Native Plants in Maine's Ecosystem
Native plants provide the foundation for Maine’s ecosystems. They support wildlife by offering food, shelter, and breeding grounds for various species. Native plants have co-evolved with insects, birds, and mammals, creating complex interdependencies. For instance, many pollinators, such as butterflies and bees, rely exclusively on native plants. These plants also contribute to soil health and water regulation, maintaining ecosystem stability.
The Impact of Invasive Plants on Maine’s Ecosystem
Invasive plants disrupt these established relationships. They often lack natural predators in their new environment, allowing them to grow unchecked. By taking over large areas, invasive plants decrease habitat availability for native species, reduce biodiversity, and alter soil composition. Additionally, invasive plants can disrupt food webs, as native herbivores and pollinators may not recognize these foreign species as sources of food or shelter.
How Invasive Plants Spread
Invasive plants spread through various mechanisms, both natural and human-induced. Wind, water, birds, and animals can carry seeds across large areas. Humans inadvertently transport seeds on clothing, equipment, or through landscaping practices. Once an invasive plant establishes itself, its rapid growth and high seed production enable it to dominate new areas quickly, displacing native species.
Four Invasive Plants and Native Alternatives
Maine’s beautiful and varied landscapes are vulnerable to several invasive plants that can displace native species and alter ecosystems. Here are four invasives commonly found in Maine, along with native alternatives that can help restore ecological balance.
1. Japanese Barberry (Berberis thunbergii)
Impact: Japanese barberry alters soil chemistry, creating an environment less suitable for native plants. It also provides ideal conditions for ticks, leading to an increase in their population.
Native Alternative:
Winterberry (Ilex verticillata): It thrives in wet soils and supports local wildlife with its berries.
Black Chokeberry (Aronia melanocarpa): It's known for its resilience in various conditions and support of pollinators.
2. Burning Bush (Euonymus alatus)
Impact: Burning bush, also known as winged euonymus, spreads aggressively in natural areas, creating dense thickets that outcompete native vegetation.
Native Alternative:
Arrowwood Viburnum (Viburnum dentatum): It grows well in moist soils and provides valuable food and shelter for wildlife.
Serviceberry (Amelanchier canadensis): It's a versatile small tree or shrub that attracts pollinators and birds with its flowers and berries.
3. Norway Maple (Acer platanoides)
Impact: Norway maples are known to shade out understory plants, reducing native diversity and making it difficult for other species to thrive.
Native Alternative:
Sugar Maple (Acer saccharum): Sugar Maple is native to Maine. It’s one of the most iconic trees in the region, known for its sap production and its role in supporting forest ecosystems.
Red Maple (Acer rubrum): It’s widely distributed across the state and thrives in a variety of soil types, making it a strong native alternative.
Shifting the Balance: Invasives to Natives
Replacing invasive plants with native species requires careful planning and commitment, but the ecological benefits are well worth the effort. When transitioning your garden from invasives to natives, consider the following tips:
Identify and Remove Invasives: Use resources like the Maine Natural Areas Program's Field Guide or iNaturalist to accurately identify invasives.
Select Native Alternatives: Research plants that provide the same benefits as the invasives you’re removing. For example, if you’re replacing an invasive ground cover, choose a native ground cover that thrives in similar conditions.
Choose Nativars Wisely: Nativars are cultivated varieties of native plants. While they offer aesthetic variety, they may not always provide the same ecological benefits as the wild types. Opt for nativars that retain essential features, such as flower shape and color, that attract pollinators.
Buy from Reputable Sources: Avoid plants that may have been treated with pesticides harmful to pollinators. The Wild Seed Project and the Native Plant Trust’s Garden in the Woods both provide lists of nurseries that sell true natives.
Consider Growing from Seed: Starting natives from seed can be a rewarding way to cultivate a garden with minimal environmental impact. Wild Seed Project provides guides on how to grow various native plants from seed, allowing you to support local ecosystems directly from your garden.
Resources for Learning More
Here are some resources that can aid you in identifying invasive plants, learning about native alternatives, and sourcing plants for your garden:
Maine Natural Areas Program: Offers a free PDF guide on invasive plants, fact sheets, and an advisory list of plants to avoid.
iNaturalist and iMapInvasives: Useful for identifying and reporting invasives in your area.
DACF Horticulture Program: Provides a "Do Not Sell" list for invasive plants.
Wild Seed Project: Features a comprehensive list of plants by growing conditions, a nursery list for native plants, and publications on native plant landscaping.
Garden in the Woods (Native Plant Trust): An excellent resource for viewing native plants in naturalized settings.
Recommended Books
Doug Tallamy’s Books: Doug Tallamy’s works, such as Nature’s Best Hope, Bringing Nature Home, and The Nature of Oaks, offer insights into why native plants are crucial for ecosystem health.
Integrated Landscaping: Following Nature’s Lead by Chase-Rowell, Hartnett, Davis, and Wyzga: This book provides practical guidance for creating landscapes that support native species and biodiversity.
Conclusion
Opting for native plants over invasives in your garden is a significant step towards preserving Maine’s natural beauty and ecological health. Native plants not only maintain biodiversity but also offer better support for local wildlife. By choosing to grow natives, we can contribute positively to our environment, creating landscapes that are resilient, sustainable, and vibrant.
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