Oak Woodlands at Pleasant Valley Conservancy

The contrast between the north-facing and the south-facing slopes at Pleasant Valley Conservancy is extreme. If one stands at the top of the ridge and looks south, one sees open oak savanna and prairie. Looking north, one sees a dense oak woods. The north-facing slope, which is almost always in the shade, is cool and moist, offering conditions favorable for dense growth of trees. Snow remains long on the north slope.

Although there was some clearing of the oak woods at Pleasant Valley Conservancy many years ago, much of the woods remains as it would have been before settlement.

In contrast to the savanna, the oaks in the north-facing woods are not open-grown. They are fairly close together, growing tall and reaching for the sunlight. Because the north-facing woods is heavily shaded, the forest floor is cool and damp. Because of this, these woods probably rarely if ever burned.

Because the north-facing woods is cool and moist, the plant understory is completely different from that of the south-facing slope. The predominant flowering plants here appear early, before the leaves are out. They flower, set seed, and senesce. Plants of this type are called spring ephemerals. At Pleasant Valley Conservancy spring flowers start to appear in early to late April and flourish up to the time when the oak leaves appear, which is usually mid May. After leaf-out, there are very few flowering plants on the forest floor, due to insufficient sunlight. During the summer the predominant plants are ferns, which are able to grow with reduced sunlight.

The tree canopy of the north woods as measured with a fish-eye lens are 90% or higher, and the amount of light available on the forest floor is probably less than 10% that found in savannas. The only places in oak woodlands where forbs are found in significant amounts during the summer are "canopy gaps", which are clear areas where trees have come down, either because of disease, or by windthrow.

Some of our most showy wildflowers are among the spring ephemerals (see Photo Gallery and species list below).

Restoration Work in the Oak Woodlands

Most of the emphasis of our restoration work has been on the oak savannas, but as resources permit, work is being carried out on the oak woods.

Controlled burns Since we started restoration work 13 years ago, we have done three large controlled burns in the oak woods. This is probably three more than has ever been done there.

The first controlled burn was done by the Prairie Enthusiasts in late October (Hallowe'en) 1999. Probably because of the unusually dry fall, this was a very successful burn. The spring ephemerals responded very well, and we had probably the largest display of large yellow lady slipper orchids we had ever seen. This may have been the only time that most of this woods had been burned since presettlement.

For years we waited for the right conditions to carry out another woodland burn. Finally, in spring 2007 everything was right and another burn was done. Again, the spring ephemerals responded well.

Encouraged by a new grant from the USDA Wildlife Habitat Incentives Program, we had a third fairly successful burn in October (Hallowe'en) 2008. The air photo below shows the results. About 25 acres burned.

What have these burns accomplished? They have helped keep the woods open and relatively free of invasive brush. They have definitely promoted the growth of spring ephemerals as well as the ferns. The maidenhair ferns, which do very well at Pleasant Valley Conservancy, really seem to thrive after a burn.

Time of year for the burns

Two of the three burns were done in the fall and one in the spring. Fall burns aren't often done by prairie people, but this was when the Native Americans always burned. It makes sense to burn the woods in the fall. One important reason is that in the spring one always has snow to contend with on the north-facing slope. Our snow often lingers there until early April, and then it takes a while for the forest floor to dry out. In the fall, we burn before the snow comes. By late October, most of the bur oak leaves have fallen, providing fresh fuel for the burn.

The day we burned in fall 2008 was especially good. It was very warm, the humdity was low, and the oak leaves carried fire fairly well.

Control of Woody Invasives There were lots of exotic honeysuckles and buckthorn in the north-facing woods. Although fire temporarily kills woody species, it does not eradicate them. Dormant buds in the soil are not affected, resprout, and the shrub continues to thrive. The most economical way of eradicating shrubs is with the use of herbicides.

In January 2006 we carried out an extensive herbicide project to control invasive shrubs in the oak woods. Although these shrubs were not as dense in the woods as in the savannas, there were quite a few large buckthorn and honeysuckle. The approach used was basal bark treatment with triclopyr (Garlon 4) in oil. This work was done by an outside contractor. Approximately 23 acres of the oak woods were treated. A series of swaths about 100 feet wide were marked, beginning at County Highway F and continuing straight up the hill to the upper ridge. A worker walked up each swath, moving back and forth and spraying the base of each undesirable shrub. The procedure took about 7 worker-hours per acre. Although costly, this approach was much less expensive than cutting and treating, and caused little damage to the woods.

The shrubs did not leaf out in the spring and gradually toppled over during the succeeding years.

Honeysuckle area at the west end

There is one bad honeysuckle area, about 3 acres, at the west end of the north woods. This is an area that had been logged at one time, opening up the habitat and providing light for proliferation of shrubs. This area consisted of almost solid honeysuckles.

During the late fall/early winter of 2006, a contractor cut all these honeysuckles and treated the cut stems with glyphosate. Large piles were made of the cut slash, and most of these piles were burned during a snow period in the winter.

Although this work eliminated the large honeysuckles, it did not eliminate the seed bank. New honeysuckle growth developed over this whole area and had to be dealt with. Because the winters 2007-2009 were heavy snow years, work on this honeysuckle area could not be done until early spring 2010. At that time, Susan, Amanda, Marci, and Tom spent several days herbiciding (by basal bark with Garlon 4) all of this honeysuckle. The area was then burned on 12 April 2010 (see photos below). This burn was moderately successful, but further work in this area will be needed in the winter 2010-2011, if the snow cover cooperates.

Burning the oak woodland (part of Unit 15) on 12 April 2010. The honeysuckles in this area had been herbicided (basal bark) before the burn.

The day after the burn in the oak woods, in an area where the burn was fairly successful. Getting an oak woods to burn requires a big burn crew and lots of drip torch fuel.

Access to the Oak Woods

We maintain a modest trail through the middle of the oak woods. This trail starts at the top of Unit 1 just above the quarry, and continues more or less along the middle of the north slope. About three-quarters of the way along, the trail forks. One fork goes steeply up and ends at the woods road in the savanna. The other fork continues east and eventually climbs to the west end of Toby's Prairie. This trail is shown as dashed blue lines on the management trail map.

Although this trail is interesting at any time of year, it is best taken in mid-May when the orchids are in bloom.