Salem Maritime National Historic Site
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  • Invasive Species

    Norway maple (Acer platanoides)


    Biodiversity: biological diversity; a measure of the diversity of life (species) in the world or in an ecosystem.

    Monoculture: one plant species dominating a forest or ecosystem.

    Wind dispersed seeds: plant seeds are carried sometimes long distances by the wind, or "flutter" to the ground.

    Nonnative species: a plant, animal, or fungus found outside its native range; introduced intentionally or accidently by humans.

    Native species: a species that naturally occurs without human intervention in a region or ecosystem.

    Invasive species: a nonnative species that has a negative impact on the environment.

    Audio Transcript

    As you travel down the Nature Trail, count how many different species of trees you observe. Even if you don’t know their names, can you tell one species apart from another? 

    The diversity of species in an ecosystem is important. Because as we’ve learned, plants and animals are always interacting and depending on one another. When an ecosystem supports a variety of life, there’s inevitably a variety of food, shelter, and resources. Scientists study this biodiversity to understand the health of an ecosystem.  

    The opposite of a biodiverse ecosystem is a monoculture, where one plant species dominates a landscape, and doesn’t allow space or resources for other plants to grow.  

    Years ago, the town of Saugus, along with numerous other New England communities, lined neighborhood streets with Norway maples. They were a good choice for street trees. They grow large, rounded crowns, creating welcome shade on hot, sunny days. In the autumn their leaves turn a beautiful bright yellow. And they’re hardy and tolerant of harsh conditions. They can grow quickly almost anywhere.  

    The one factor that makes the Norway maple less than ideal, is it's not native to North America, but to Europe and Asia. It was first introduced here sometime in the mid 1700s.  

    The Norway maples planted on Saugus streets grew quickly, and their wind dispersed seeds found their way to the Nature Trail. 

    Not all nonnative species are invasive. A species becomes invasive when it displaces and threatens native species.  

    Tall Norway maples with large crowns began to grow, shading out other plants. No natural diseases, fungi, or herbivores existed in the food chain to keep the species’ growth in check, and native species like the sugar maple and shagbark hickory couldn’t compete. And loosing those trees meant loosing sugar maple sap, rich in carbohydrates, and hickory nuts, rich in protein. And loosing those resources meant it was harder for the Eastern grey squirrel to survive long, cold winters. Threatening squirrels meant threatening red-tailed hawks. Up and across the food chain, a monoculture habitat can’t support a diverse ecosystem.