A "wolf" tree in a former pasture

The term "wolf tree" is often used by foresters to indicate ancient open-grown "relic" oaks that have survived in degraded oak savannas. Open-grown oaks are "indicators" of former oak savannas and provide strong justification for oak savanna restoration work.

At Pleasant Valley Conservancy we had (have) large numbers of open-grown oaks. These oaks survived through generations of agricultural activity and are still present in our restored savanna.

What happens when land containing one or more open-grown oaks is neglected? Without fire, and without brush/tree clearing, the land surrounding these oaks gradually turns into a dense forest of brush and invasive trees. The open-grown oaks become crowded and their lower branches shaded. Depending on how long the former savanna is neglected, the oaks may be seriously damaged, although perhaps still struggling along.

Yesterday, while doing the annual Audubon Christmas Bird Count, I spied a "wolf" tree (white oak) that I had overlooked. In summer, with so much greenery around, such a tree does not stand out, but in winter cover it is very obvious. As the photo shows, this venerable tree is covered with gnarled remains of branches that had been shaded and killed. A few branches still remain, although some of these are probably dead also. This tree is easy to find, especially this time of year. In the background of the photo is Toby's Prairie, and the service road is just to the north.

I'm not sure why I missed this tree earlier, but it stands out well today.

This tree is in the middle of an area that was classified as "stump pasture" in the 1938 Wisconsin Land Use Inventory. This tree stands out clearly in the 1937 photo shown below.

GIS 1937 photo showing the location of the "wolf" tree. The open land surrounding
the tree was classified as "stump pasture". 

 In Henry David Thoreau's time such oaks were called "pasture" oaks. See the following quotation from Thoreau's journal:

It is evident that the pasture oaks are commonly the survivors or relics of old oak woods,---not having been set out of course, nor springing up often in the bare pasture, except sometimes along fences.....Such trees are often found as stragglers beyond a fence in an adjacent lot. Or, as an old oak wood is very gradually thinned out, it becomes open, grass, and park-like, and very many owners are inclined to respect a few larger trees on account of old associations,  until at length they begin to value them for shade for their cattle. These are oftenest white oaks. I think that they grow the largest and are the hardiest. This final arrangement is in obedience to the demand of the cow. She says, looking at the oak woods: “Your tender twigs are good, but grass is better. Give me a few at intervals for shade and shelter in storms, and let the grass grow far and wide between them.”
What a great description of an oak savanna!