Feb 24, 2020
Balance & Barrier: A Slow Explosion of Damaging Forest Insects
Play • 23 min

A biological invasion is an enormous increase in population of some kind of living organism. It happens when an organism — like an insect — arrives somewhere beyond its previous range, when it breaks out past its natural barrier, unbalancing the biological order. More than 450 non-native insects have invaded our forests and urban trees since European settlement. In this series, we'll explore four of these insects, and the scientists studying and combating these pests.

In 1957, a British ecologist, Charles S. Elton, gave three radio presentations entitled “Balance and Barrier.” Within a year, he had expanded these ideas into what was to become a bible for practitioners of a burgeoning new science: invasion biology. In a tribute to those broadcasts, this six-part series will explore biological invasions — and their repercussions — in the Midwest and the Northeast.

Related Research:


  • Therese Poland, Project Leader/Research Entomologist, Northern Research Station, Lansing, Michigan
  • Sandy Liebhold, Research Entomologist, Northern Research Station, Morgantown, West Virginia
  • Robert Haight, Research Forester, Northern Research Station, St. Paul, Minnesota

Produced by the USDA Forest Service Northern Research Station.

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