The Three Rivers Trail crosses and runs along our major rivers. Before white settlement, our rivers had many oak savannas on the upland parts of their river valleys.
Bur and white oak trees along the Three Rivers trail probably owe their existence to once being part of an oak savanna. Oak savannas were found along our rivers with U-shaped valleys near the top of the slope, where the prairie met the forest.
As you may know, prairies depended upon fire to thrive. Without fire, Iowa prairies would have been over taken by woody plants and soon become forest. The wetter river bottoms were resistant to fire and were typically wooded. Prairie plants evolved to thrive and, in some cases, even depend on fire.
As you might imagine, there developed a transition zone between the prairie and forest: the oak savanna. Large oak trees are fire resistant. Small oak trees will grow back after being burnt to the ground on their existing root system.
This spot on the landscape where prairie fires burned themselves out turned out to be great for the oaks. These fires weren’t large or frequent enough to affect the large oaks, but they keep in check other woody plants that competed with smaller oaks.
Oak savannas, like all transitional ecosystems, were places that teemed with fauna. In addition to species that we would recognize like bison and elk, Iowa had its own pachyderms, sabertooth cats, and giant ground sloths.
If you see an oak tree along the trail, appreciate that it somehow out competed all the invasive species like honeysuckle and other native trees. Imagine an oak forest running along the ridge above the river. Think about the heard of elk or the odd mastodon that may have stopped in the shade to munch on the understory.
