Tom's Blog

Thursday, December 10, 2015

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.

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.
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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