Tom's Blog

Monday, April 1, 2013

Oak regeneration in savannas

Most of the literature on oak regeneration deals with silvicultural matters, such as production of oaks for harvest. Oak regeneration must also be considered in savanna restoration, because the large, open-grown oaks that we encourage will eventually die and some replacement is needed.

The discussion here deals with what we call the White Oak Savanna (Unit 12A) a seven-acre site which has a large number of handsome open-grown oaks. This was the first savanna area we restored, in the year 2002. We based the work on the 1937 air photo, a portion of which is shown here. The large, open-grown oaks are very evident. The 1938 Bordner land use survey classified the area between the two ag fields as "stump pasture." Most of the large oaks present in 1937 are still present, but (presumably) much bigger.
The White Oak Savanna in 1937. The two surrounding fields were cropped but are now prairies.
 When we started restoration, the goal was to remove all of the trees that were crowding the open-grown white oaks. Although there was a mixture of tree species, including walnut, box elder, and cherry, many of the trees were black oaks (Quercus velutina), which are notorious for rapid growth. (Many of the black oaks were almost the same diameter as the large white oaks, but were many years younger.) Restoration involved removal of a huge amount of wood. However, there were patches of small-size (5-10" diameter) white oaks which, since they were not crowding the large oaks, were left. All of the smaller trees with leaves in the photo below are white oaks of this sort. These trees are large enough to be fire-resistant. We have considered removing most of these small white oaks, since we don't really need them, but we'll probably leave them until they start causing problems. (It would only take a day or two to get rid of them.)

Kathie walking up the White Oak Savanna Trail. Two of the original large white oaks are visible. Most of the small trees with leaves are also white oaks.
 In addition to these areas of smaller white oaks, there are quite a few black oak grubs, such as the one shown in the photo below.

The small plant with leaves is a black oak grub. There are dozens of such grubs scattered across the Savanna.

Where have these black oak grubs come from? Recall that we cleared this savanna of black oaks in 2002 and it has been burned every year since then. Since there is no longer a black oak seed source, these grubs were probably here when our restoration work began. Each year they are killed back by the fire, and resprout again, a phenomenon typical of oak species. As long as we burn at regular intervals, we can keep them under control. Because of their presumed extensive root systems, I'm not sure if they could be eradicated with herbicide, with or without cutting.


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