More on hazel (Corylus americana)
A recent blog post from Chicago about protecting hazel from fire and deer browse brings me to a further discussion of this widespread shrub.
Hazel (Corylus
americana) is one of those plants that people love until they have it,
after which they may discover that it is invasive and nasty, and then they hate
it.
Why is it sought after? For its wildlife value. Its leaves,
twigs, and catkins provide browse for deer and other ungulates. Its nuts are
eaten by small mammals, birds, and deer. Beaver eat the bark. In America it has
been cultivated as an ornamental since the 18th century. It is also
cultivated commercially for its nuts.
However, it is an early successional species, which, left unchecked, can destroy native prairies and savannas, making way for dense forests. It is a dominant or co-dominant shrub (understory
species) in maple/basswood, jack pine, paper birch, aspen, and northern pin oak
communities in northern Wisconsin. It can form extensive thickets in oak
savannas in southern Wisconsin. It often competes with hardwoods and pines and
because of shading and aggressive growth, it is considered a major deterrent to
successful forest regeneration. It is blamed for the failure of red pine
regeneration in Minnesota. There has been extensive
study on hazel at Minnesota’s Cedar Creek Natural History Area.
Hazel can potentially form large shrubs, 3-10 feet tall, and
because it is rhizomatous, can form dense thickets. Such thickets were
described by early observers in the Midwest.
Although hazel is a prolific seed producer, most of the
seeds are eaten by animals and birds; the most important mode of reproduction
is by rhizomes. After initial establishment of a shrub, extensive aerial stems
(root suckers) can form from underground buds. It is shade tolerant and can
grow at light intensities of 15% or less. Below a dense hazel stand light
intensity may be 2-7% of full sun (Stearns) so that it can crowd out or shade
other plants. Competition for moisture is also severe.
Hazel is easily top-killed by fire, but it readily resprouts
from rhizomes, so that annual burning does not eradicate but actually increases
the hazel stem density. However, stems on burned sites are shorter and smaller
than those on unburned sites. Where fire is excluded, a
heavy density of hazel may develop, greatly suppressing tree growth.
Although hazel can be controlled by annual fire, it is never
eradicated. Thus, if fire does not occur for a few years, hazel growth may take
over and suppress desirable understory plants. Once a dense hazel thicket has
developed, satisfactory fire will not be possible due to a lack of fuel.
Our hazel experiences:
In Black Earth Rettenmund Prairie prairie, whose units have been burned
on a two-out-of-three-year cycle for many years, hazel recently began to
flourish. Clones with as many as 250 stems develop within a single growing
season. (See photos at end of this post.) Because of the stem density, such clones never completely burn, so that
eradication of hazel requires the use of herbicide.
At Pleasant Valley Conservancy, hazel has been a persistent
problem in savannas and prairie edges. Annual fire continuing for at least ten
years has not eradicated hazel, although none of the hazel patches are very
tall. Only herbicide can control it.
Recommendations:
A hazel bush is handsome and its leaves are very colorful in
the fall. However, if hazel is desired for wildlife, then it must be rigorously
controlled. Select choice bushes and eradicate all the rest. Especially in savannas and prairie borders, careful attention to
control must be exercised. A three year burn cycle is recommended, two burn years
followed by a nonburn year. In the nonburn year, hazel should be surveyed in
mid-summer and a few choice bushes should be retained, and all the rest
eliminated by herbicide treatment (see below for herbicide use).
Herbicide treatment:
- New spring/summer growth. Canvas the site and spray all plants at the rosette stage with 3% Garlon 3A in water.
- Small bushes can be treated with 20% Garlon 4 in oil by basal bark any time during the late summer or early fall. Since hazel bushes can easily be found in the fall due to their colorful leaves, this is an excellent time to treat, although it is possible to treat anytime, including winter, but before the following spring burn.
- Large bushes should be cut with a brushcutter and the cut stems and stumps treated with Garlon 4 by basal bark.
References:
Forest W. Stearns 1974. Hazels. In Gen. Tech. Rep. NE-9, Northeastern Forest Experiment Station.
Gleason, Henry A. Torreya Vol. 13, August 1913.
Hazel clone that developed in a single growing season at Rettenmund Prairie |
Over 250 stems were counted in this clone. Also, spreading occurred by rhizome extension. |
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