Maple trees (Acer) are recognized across the Northern Hemisphere for their shade and vibrant autumn foliage. The question of whether maples are invasive is common, but the answer depends entirely on the specific species and the geographic location where it is growing. Understanding the true impact requires distinguishing between an ecological invader and a species that is simply aggressive in a garden setting.
Understanding the Definition of Invasive Species
An invasive species is defined as one that is non-native or alien to the ecosystem under consideration. Its introduction must cause, or be likely to cause, economic or environmental harm, or harm to human health. This harm usually involves displacing native plants, altering the food web, or changing ecosystem processes. A non-native species that establishes a self-sustaining population without causing widespread damage is often called “naturalized.” The term “invasive” is reserved for non-native species that outcompete and disrupt the natural balance of a region.
The Norway Maple: A True Invasive Threat
The primary reason for the concern about invasive maples is the Norway Maple (Acer platanoides), which is native to Europe and Western Asia. Introduced as an ornamental tree, it meets the full criteria for an invasive plant throughout much of the United States and Canada. The Norway Maple establishes dense canopies that cast heavy shade, preventing native woodland plants from growing beneath it. Its shallow, fibrous root system aggressively outcompetes native understory plants for water and nutrients, reducing local biodiversity. The tree is also a prolific seed producer; its shade-tolerant seedlings form thick mats on the forest floor, further displacing native flora.
Native Maples and Aggressive Seeding
In contrast to the Norway Maple, native North American species like the Sugar Maple (Acer saccharum) and Red Maple (Acer rubrum) are essential components of their ecosystems. These maples are often perceived as invasive by homeowners because of certain aggressive growth habits. The most common complaint involves the sheer quantity of “helicopter” seeds, or samaras, they produce each spring. While this can be a nuisance for gardening, these native seedlings do not pose the same threat of ecological displacement as the non-native Norway Maple. Some native maples also develop large, shallow root systems that can lead to problems in urban environments, such as lifting sidewalks or cracking driveways. These behaviors are examples of a native species being aggressive, not ecologically invasive.
Practical Control and Removal Strategies
Managing problematic maples requires identifying the species, as control methods differ significantly between native and invasive varieties. For the non-native Norway Maple, removing the mature tree is the most effective solution to stop seed production. Small seedlings can be manually pulled or dug out, especially when the soil is moist. For larger trees, cutting the tree down followed by an immediate application of a systemic herbicide to the freshly cut stump is necessary to prevent re-sprouting. Alternatively, a mature tree can be girdled by removing a continuous ring of bark and cambium around the entire trunk, causing the tree to die slowly.
Managing Native Seedlings
Managing the abundant seedlings from native maples is typically less intensive. In lawns, regular mowing easily controls new maple seedlings before they establish a substantial root system. For garden beds, a thick layer of mulch can suppress germination, and any seedlings that sprout can be easily hand-pulled. Choosing the right native maple for a specific location, such as one with deeper root growth, can help avoid future conflicts with infrastructure.