By Bill Kleiman, Nachusa Grasslands, TNC
The photo above shows mostly bur oaks growing in a prairie restoration. We planted the bur oaks in 2006, but first we planted prairie in 2001. This makes the start of a savanna. The 2001 prairie planting was maturing and we decided to plant some acorns into the five year old prairie where it approached the oak woods so we would not have an abrupt prairie to oak woods edge. It worked. Those shrubs are all oaks, many bur oak. I know they are from the acorns we planted because we planted bur oak acorns and the oaks near the edge are black and white and northern red oak.
We burn this unit frequently and the nearest oak shrub shows a few stems that were top killed by fire. In another place on the preserve where we have frequent fire there is one or two small tree sized oak for every 100 oak shrubs. So frequent fire supports development of savanna. I bet these open savanna were a common sight a few centuries back.
Above photo is when I turn around and shoot the opposite direction which shows the old oak woods adjacent to this planting. Shagbark hickory, white oak, northern red oak. A cup plant in the foreground. There is very little oak recruitment in this woods in spite of a frequent fire regime.
Above is seasonal crew Stephanie in 2006. She and I used dibble bars to plant oak acorns. Bernie uses a tile probe with similar effect. I remember getting blisters on my hands as the soil of the new planting was hard and dry. A study on this same field by soil scientist Mike Konen showed that the soil became less dense about ten years after planting to prairie. It took at least five years to notice any oaks emerging.
Above is a later photo from a different planting of acorns. Our dibble bars in 2006 made just a small dent in the ground. I think we scuffed in the opening with our boots.
So to restore a savanna, try planting a prairie first, and burn it frequently.