Thursday, November 12, 2015

The impact of invasive species

Earlier this week I shared a photograph of the tunnels created by Emerald Ash Borer larvae (Agrilus planipennis) under the bark of a Green Ash tree (Fraxinus pennsylvanica).  This photo was taken on Monday at Chipp-A-Waters Park in Mt. Pleasant.

Emerald Ash Borer galleries in a Green Ash log

As the larvae chews through the layers of phloem, xylem, and cambium under the bark of the ash tree, it disrupts the flow of water, dissolved minerals, and sugar throughout the tree.  If there are enough beetle larvae making these tunnels, the tree soon dies.

Dead Green Ash trees at Chipp-A-Waters Park

Initially these dead trees will support a large population of birds such as woodpeckers that feed on the ants and beetle larvae attracted by the dead tree.  Over the course of a few year, the ash trees will begin to topple.  When they fall, they often knock over or damage other living trees.

Dead, dying, and leaning ash trees - the one knocked over a Red Oak (stump in foreground) as it fell.

At Chipp-A-Waters Park, like many other places, has a lowland habitat that is largely dominated by Green Ash trees.  When these trees die, they open up the canopy and allow more sunlight to reach the forest floor.  This increase in sunlight allows allows the seed bank lying in the soil to sprout.  Unfortunately much of the new growth is dominated by invasive species such as European Buckthorn, non-native honeysuckles, and Garlic Mustard.

Garlic Mustard with honeysuckle in the background

A honeysuckle thicket and downed Green Ash trees

Right now the forests of Michigan (and many other states) are experiencing the short-term effect of the ash trees dying out.  What the long-term effect will be remains to be seen.  Will a different nativer species take their role in the canopy?  Will our forests become so overgrown with invasive shrubs that the canopy fails to regenerate?  Or will something else happen?  It will be interesting to find out.

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