Hazel is a native shrub that is widespread in Eastern U.S.
It is found in every county in Wisconsin, and was occasionally reported by the
surveyors in the original public land survey as part of the plant understory. Although
not considered an invasive plant in Wisconsin, it is a serious problem in the
red or jack pine forests of Minnesota. It is also considered a problem in other
areas, as the following quote from the Flora of North America attests: “Corylus
americana is a weedy
species, sometimes considered a pest in carefully managed forests.”
During our early savanna restoration work, based on the
prevailing sentiment in southern Wisconsin, we either ignored hazel or allowed
it to grow, in some cases even encouraged it. Now we realize that this may have
been a mistake.
Although it grows rhizomatously, its rhizomes only grow a
short way before they send up new shoots. Thus, in contrast to sumac, gray
dogwood, and prickly ash, hazel often grows as tight, compact bushes. A single
bush like this may remain compact for a number of years, although its duration
in this well-behaved capacity is unpredictable.
Under some conditions a single hazel bush may turn into what
is called a “hazel thicket”.
In his pioneering paper on the relationship between forests
and fire, Gleason noted that the margin between prairie and forest consisted
chiefly of hazel, “a shrub which is not seriously affected by repeated
burning…. There is one record known to
the writer of a large hazel thicket, covering several acres at the western edge
of an upland forest, and several such records of scattered thickets of hazel in
the middle of the prairie.” (Gleason, Henry A. 1913. The relation of forest
distribution and prairie fires in the Middle West. Torreya 13: 173-181.)
A survey of the literature reveals a number of mentions of
“hazel thickets” associated with either prairies or savannas. Thus, hazel “can”
become a problem, although the conditions leading to this situation are not
clear. At any rate, it seems obvious to me that it would be foolhardy to allow
hazel to “run amok”.
At Pleasant Valley Conservancy I have been seen several sites
where hazel seems to be getting out of hand. At the south side of Toby’s
Prairie, in a former aspen zone, hazel has been spreading even in the face of
annual fire. It has also spread extensively in some areas of the White Oak
Savanna (Unit 12A), also burned annually. Both of these areas seem to have the
potential of becoming bad, so we are killing them this winter by Garlon basal
On the other hand, there are several hazel bushes along the
margin between the Ridge Prairie and the East Basin that seem to be well behaved.
They were left ten years ago when we cleared all the honeysuckles away, and
although they have bulked up they have not spread.
These are savannas. How about prairies? Here I think it
depends upon the history of the site, what I call the “legacy”. At Black Earth
Rettenmund Prairie, where hazel was present before restoration work began,
there is a large hazel clone on the Saddle that has survived dozens of
prescribed burns. Also, on the knoll at the top of the North Unit, where the
woodies formerly consisted of prairie willow and sand cherry, both relatively
benign, in 2012 many clones of hazel appeared. Even more disturbing, they were not
only spreading rhizomatously, but were sending up suckers (see photo). In this clone
I counted over 350 shoots.
conditions, it seems reasonable to control the hazel, and this is what we are
|New shoots of a hazel clone spreading away from the main shrub.|