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.

The air photo shown here illustrates the contrast well. The tree density on the north-facing slope is high; the canopy is mostly completely closed, whereas the savanna on the south side is partly open, with scattered open-grown oaks.

Air photo (from 2010) illustrating with GIS the north-facing woods.

Visiting the oak woodlands

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 map above.

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

There are three ways then to view the north woods:

1. A stroll along County F shows the woods from below;
2. A walk along the North Fire Break, which can be reached from a side trail at the west end of Toby's Prairie
3. The North Woods Trail, which is especially nice in mid-May when the spring wildflowers are in bloom.

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. In the dense shade of summer, the principal flora is ferns, of which maiden hair fern is the most frequent and attractive.

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 two most frequent members of the spring flora are trillium (Trillium grandiflora) and yellow ladyslipper orchid (Cypripedium pubscens). Some of our most showy wildflowers are among the spring ephemerals (see Photo Gallery and species list below).

The tree database

All trees larger than 10 inches in diameter have been tagged, ID'd, measured, and entered into our database. The photo below (prepared with GIS) shows the distributions of the three dominant oak species, Northern Red (Quercus rubra), Hill's (Q. ellipsoidalis), and White (Q. alba). On the north slope the most frequent species is red oak, although substantial numbers of white oaks are scattered about. Hill's oak is only found in a patch near the top of the ridge. (There are many Hill's oaks in another cluster at the east end of the Conservancy.)

GIS map showing distribution of red, white, and Hill's oaks on the north-facing slope.

The tree canopy of the north woods as measured with a fish-eye lens is 90% or higher, and the amount of light available on the forest floor is probably less than 10% of 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.

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.

Although much of the woods remains as it would have been before settlement, there were two areas that had been cleared many years ago. These can be seen on the 1937 air photo. A large area at the far eastern end of the woods, near the property line, had been cleared some years before the 1937 photo, and had become a brush patch when this photo was taken. Presumably this area, easily reached, was cleared for firewood. Another area in the middle of the woods, across from where the Duhr driveway is today, had also been cleared. It is interesting that this formerly cleared area is now the site of a large population of Trillium grandiflora is .

Restoration Work in the Oak Woodlands

Although most of the emphasis of our restoration work has been on the oak savannas, work has being carried out on the oak woods as resources have permited.

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

Honeysuckle area at the west end There was 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 the following 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 this area was burned again in November 2010 (see below)..

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.

County Highway F

Pleasant Valley Conservancy owns about 2500 feet of Dane County Highwaty F. This roadside has significant prairie and savanna flora, and has been an area that we have been managing since 1999. This area was an important seed source in the early days of our restoration work. The importance of this roadside was first pointed out to us by Brian Pruka, and Paul West encouraged us to start collecting seed there. Although in the early years the Dane County road crew was somewhat uncooperative, since around 2005 we have had great cooperation following an agreement that we would cut and manage vegetation in this area.

There have been several management problems. Initially we had to deal with woody invasives such as honeysuckle and buckthorn ,, as well as aspen. When we began management the honeysuckle was especially bad on the upper slope where the county road mower did not reach. We continue to manage woody vegetation, although mostly now it is native species such as willow, elderberry, and viburnum. The goal here is to keep the roadside free of woody vegetation so that the prairie and savanna flora can flourish.

Wild parsnip was a major problem in the early years, but diligent hand pulling brought this under control and we have had no problems since the late 2000s. Although sweet clover was never a major problem, scattered patches were present and continue to require attention.

We were encouraged by the response to brush removal of prairie and savanna species, which seemed to have been living in a suppressed state. Those species which we have collected extensively on County F include Aster sagittifolius, Ceanothus americanus, Desmodium canadense, Euphorbia corollata, Gentianella quinquefolia, Hypericum pyramidatum, Krigia biflora, Pediculus canadensis, Polygala senega, Solidago nemoralis, Taenidia integerrima, Veronicastrum virginicum, and Zizia aurea. See this link for a detailed species list.

Further work on the County F roadside was initiated in 2011 under a LIP grant. See details at this link.

Controlled Burns

Since we started restoration work 15 years ago, we have done some large controlled burns in the oak woods (1999, 2007, 2008, 2010).

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 was probably the first 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.