Clearing Invasives from Savannas and Woodlands

…on the fertile Corn Belt soils, all our oaks are headed for oblivion, except where ecological restoration or other intentional management protects them.

 Stephen Packard


The Tallgrass Restoration Handbook

Edited by Stephen Packard  and

Cornelia F. Mutel



Clearing Invasives from Savannas and Woodlands

 By Mid-November,  in the Chicago region, most of the leaves have fallen from the trees.  Except–what is that shrubby, choking undergrowth that’s  still hanging unto its dirty green foliage in the understory of our oak savannas and woodlands?  You know the answer–it’s Common Buckthorn (Rhombus cathartica), an alien imported from Europe in the late 1800’s.   Buckthorn leafs out early and abcisses late, not allowing sunlight to reach the ground level. The excessive shade keeps oak trees from reproducing, guaranteeing their eventual demise.  It also keeps native wildflowers from sprouting and  growing on the woodland floor.  Without an herbaceous carpet, the soil will soon erode away.  In addition, trees rely on the deep fibrous roots of herbaceous plants to keep them adequately hydrated.

Amur and Tatarian Honeysuckles (Lonicera maackii and L. tartarica) are other alien shrubs equally harmful to our oak savannas.    Honeysuckles flower prettily in May, but their aggressive weediness soon chokes out native plants.  “It would be difficult to exaggerate the weedy potential of this shrub,” say Floyd Swink and Gerould Wilhelm of the Amur Honeysuckle in Plants of the Chicago Region.

Still more aliens choking our woods and savannas are European Cranberry, Multiflora Rose,  Autumn Olive, and Oriental Bittersweet.

Many of these shrubs were brought to this country because their berries would feed wildlife.  Why anyone thought native plants weren’t adequate to feed native animals is a mystery.  Here is a paragraph I found in a website this morning called Forager’s Harvest.  The autumn-olive was lauded as a virtual miracle forty years ago; it was intentionally planted by the same government agencies that are now villainizing it and spending millions trying to eradicate it. Latham (1963, p. 19) expressed the prevailing attitude when he said, “These shrubs add beauty to narrow field corners, roadsides, [etc.]—with no evident danger of becoming a pest by spreading onto pastures or well-kept places.” Latham then lived in Ann Arbor, Michigan—around which, today, the autumn-olive is the most prevalent shrub, having choked out most native species. I wonder how many of the current ideas espoused by today’s natural resource managers will be laughed at in a generation. (I can name a few.)”

And here is Swink and Wilhelm’s description  of Autumn Olive in Plants of the Chicago Region:

“Introduced from Asia.  Commonly planted as an ornamental and in ”wildlife areas” as a forage plant, this species was unknown as a spontaneous element in the Chicago region flora until the late 1970’s.  By the late 1980’s it had become nearly ubiquitous in degraded open woods, railroad rights-of-way, and unmowed meadows.”

Prior to European settlement, the grasses in the savannas burned, just as they did in the prairies, keeping woody plants from taking hold.  But the suppression of fire, plus the introduction of the aggressive alien shrubs, mentioned above, has spelled ruin for our oak savannas and woodlands.

What to do?  Late fall and winter are the perfect time to cut out the brush that is choking our savannas and woodlands.  Cut the trees to the ground and paint the stump with Brush-Be-Gone or Garlon.  If you don’t want to use chemicals, you can cover the stump with black plastic and, given time, it will die.  Or you can girdle the tree trunk by removing a section of the bark encircling the tree.  Best time to do this is early spring before the tree leafs out.

And then follow up with a yearly autumnal burn.








Burnidge Forest Preserve after controlled burn.








You can use the branches from the Buckthorn to make a fence as did this homeowner.










Dr. Gerould Wilhelm conducting the first woodland burn at Morton Arboretum in the fall of 1987.












Woodland at Morton Arboretum that has had a controlled burn every fall since 1987.  The Cardinal Flower grew spontaneously.

A yearly burn is necessary, says Dr. Wilhelm.  In my area, Bluff Spring Fen and Trout Park, both Illinois Nature Preserves, are burned yearly by the stewards that result in almost pristine natural areas. On the other hand, our Kane County Forests Preserves are burned on a 3 year rotating schedule.  Better than not burning at all, but after 3 years, the areas that were burned have grown back–either from re-sprouting or from all those berries. scattered by birds.


To read an  Assessment of Landscape Management of Timberhill Savanna in southern Iowa go to this link:




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