Why Is There Paint on Hillside Trees?

By Róisín O'Flaherty

Recently you may have noticed some white lines across certain trees in the Hillside Woods. Maybe you assumed they were some poorly delivered trail markings or a minimalist Banksy project. It is neither. These white lines are part of the Hillside Woods Restoration Project’s effort to combat invasive species in our woods. Trained volunteers have marked two invasive tree species: Norway maple and tree of heaven (aka ailanthus). These trees are being surveyed so that they can be removed. Invasive species like these trees compete with native plants, offer little to nothing to native animals, and decrease the biodiversity of an area. But these aren’t the only invasives present in Hastings, so why these trees specifically?

The Norway maple has a particularly large presence in our woods, which is problematic for a number of reasons. It leafs-out early, casts dark shade and has a shallow root system, all of which disrupt the growth of native plant species that need ample sunlight to grow, especially wildflowers and the sugar maple. In a domino effect, this also affects native birds and insects, who depend on these native plants for food. The Norway maple may also serve as a host for aphids, small insects which in large numbers will damage other plants.

The second tree you need to know about is the alianthus, more commonly known as the tree of heaven, a rather misleading name. The tree of heaven produces allelopathic chemicals, which are chemicals that leach into the soil and inhibit the growth of other plants. Quite rude, really. The tree of heaven also attracts the spotted lanternfly, an agricultural pest that attacks native trees and produces a sugary fluid that encourages mold and disease. The tree of heaven’s impressive root system can buckle pavement, and it’s partly this root system which makes it very hard to get rid of. In fact, you may recognize the tree of heaven from A Tree Grows in Brooklyn by Betty Smith, in which it symbolized perseverance, especially in challenging or dangerous environments. But with the time and dedication of many, both the tree of heaven and the Norway maple can be removed and our woods can become a happier, healthier place. 

How to Identify these Two Invasives

Norway Maple

  • The leaves of Norway maples are wider than they are long. 
  • They have five distinct lobes, or sections, on each leaf. 
  • During the spring, Norway maple has clusters of yellow-greenish flowers, which mature to seed pockets with helicopter-like blades during summer. 
  • In the fall, the Norway maple turns yellow. 
The Norway maple looks very similar to it’s non-invasive native cousin, the sugar maple. Here are a few key characteristics that differentiate the Norway maple from the sugar maple: 
  • The Norway maples have white sap. If you break the stem off a leaf and see white sap then you know it’s a Norway maple. Good way to remember: white sap, snow is white, and there’s lots of snow in Norway. 
  • Norway maples have longer stems. 
  • They tend to have less bug-bitten leaves, due to the fact Norway maples are invasive and aren’t consumed by most native insects.
 
Tree of Heaven (Ailanthus)
  • The tree of heaven has long-stemmed leaves with anywhere from 10 to 40 leaflets. 
  • Its individual leaflets are a few inches long, with bumps at the base.
  • Its bark is described as looking like cantaloupe skin. 
  • It has yellow flowers in early summer to late spring, which become clusters of orange-yellowish seed pods during late summer. 
  • The tree of heaven has a pungent odor. Its distinct smell has been described as burnt peanut butter, “that new gym smell,” or burning rubber. Next time you spot one in the woods, crack a stem or leaf, take a whiff, and you can decide for yourself the odor. 
The tree of heaven may look similar to wisteria, another invasive plant. However, you can easily pluck tree of heaven seedlings in your garden in early spring through summer. Sprouting wisteria tends to be connected to a longer root and is harder to remove.
 
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