Oak savanna restoration; how long does it take?
I’m often asked how long it takes to restore a property or plant community. It’s difficult to answer because every property is unique. But what follows is my attempt to chronologically timeline an oak savanna restoration. Keep in mind that your restoration efforts and results will be different, but I hope this provides a better sense of expectations, and helps define what “restoring” is all about.
Begin with your goal. Is there a time period you want the land to return? Generally, restoration ecologists target the time prior to European settlement. Maybe you want the land returned to how it looked when you were a child. Try not to get too hung up on a time period. Even if we knew what the land looked like prior to European settlement, there are many reasons that preclude us from going back. A reasonable – and realistic - goal is to restore a diverse set of native plant and animal communities that scientists believe are historically appropriate. This will fall sometime before the onslaught of major land alterations and invasive species.
Let’s consider a 5-acre oak savanna that was grazed during most of the twentieth century:
Year 0 -1 Assessment and study: Historical aerial photos reveal a gradual closing of the tree canopy with total closure occurring around the year 1980. The site assessment reveals a large stand of even-aged, open-grown bur oaks on the ridgetop. On the side slopes, there are black oaks, northern pin oaks and white oaks. The oaks are being “overtopped,” or shaded out, by Siberian elm, white mulberry, box elder, black locust and black walnut. The shrub/small tree layer is dense with European buckthorn and prickly ash. The herbaceous layer (grasses and flowers) is largely absent due to the dense shade of the buckthorn. The “terracing” effect of cattle paths are still visible on the side slopes.
Year 1 – 2 Active management: The first task is to save the oak trees from further decline. The initial plan calls for “daylighting” oaks by felling (cutting down) adjacent, light-competing, non-oak trees, and girdling (killing the tree but allowing it to stand) occasional trees for wildlife habitat. Early into the effort, it becomes clear the amount of fallen wood is too voluminous to reasonably handle. (Your arms are weary from all the chainsaw work, or your budget is going fast). A decision is made to remove the small trees and girdle the larger ones. The landowner, who has been struggling with the idea of killing walnut trees, decides to allow the walnuts to grow if they have potential future timber value.
Year 2 – 3 Tackling invaders: Management activities now focus on removing buckthorn and thinning prickly ash. “Cut and treat,” a method for removing unwanted bushes & trees followed by treating the stumps with an herbicide, is the management method selected. This approach promises to quickly release the ground layer (grasses, sedges and flowers) in hopes that desirable species will return. Landowner and contractor push hard, and they clear 2.5 acres of buckthorn. The visual results are immediate and satisfying. The “structure” of the savanna is returning. A few of the large trees girdled last year are dead. Others appear sick. Some seem perfectly healthy (stand by … this can take time.) The cleared buckthorn area is seeded with native grasses as called out in the management plan.
Year 3 – 4 Keep going: The remaining buckthorn are cleared and seeded with native grasses. Visually and aesthetically, the savanna looks great, and you can see completely through it now. More of the large girdled trees are dying. The buckthorn area cleared last year now has short-stature “green” plants showing up, along with some small brambles and young seedlings. Some of the buckthorn stumps are re-sprouting.
Year 4 – 5 Fire begins: The first prescribed fire is attempted, and the results are a spotty burn. The fire only carried well through areas with oak leaves on the ground. Most of the girdled trees are now dead or nearly there, and you swear you see a red-headed woodpecker using one of the dead trees. By mid-spring and early summer, it’s clear that most of the green plants in the buckthorn area, which was cleared year 2-3, are weeds such as bull thistle, mullein, burdock, Canada thistle, and the small seedlings are buckthorn. Even more troubling, invasive weeds such as Japanese hedge parsley, sweet clover and garlic mustard are found. In some areas, raspberry and blackberry brambles are rapidly increasing in numbers. It’s difficult to fight discouragement, but you press on. Management efforts to control these species begin in earnest. The first efforts focus on controlling the invasive species followed by the occasional mowing of bramble patches as time and finances allow. Some native plant species are discovered, including the grasses that were seeded. You definitely spot a red-headed woodpecker using one of the girdled dead trees. New branches are appearing on the lower trunks of the old bur oaks.
Year 5 – 6 Progress shows: The second prescribed fire is attempted. Burn coverage is better because now native grasses and oak leaves provide fuel for the burn. The first-year buckthorn clearing area is now even thicker with weeds, brambles and buckthorn seedlings. The second-year buckthorn clearing area is following the same trajectory as the first-year clearing, but this time, you are smarter and control the weeds earlier in their growth cycle. More native plant species are appearing, including yellow pimpernel, a savanna indicator species. There are now two girdled snags being used by red-headed woodpeckers.
Years 6 -10 Maintenance and time: The same management sagas continue. Prescribed fire followed by weed control, buckthorn seedling control, and occasional bramble mowing. New plant and animal species are found regularly. Oak regeneration (young seedlings) is beginning to occur. When you can pull your mind out of the dread of battling weeds, you notice that the plant composition trajectory is shifting away from invasive weeds to native species. Areas once dominated by brambles are shifting to native sedges, grasses and flowers. The natural processes responsible for maintaining the ecological health of an oak savanna are starting to kick in on their own. Patterns are becoming apparent to you such as which native species are good at out-competing undesirable species. You exploit these patterns by introducing these species’ seeds to other trouble locations. And those sacred walnut trees? You removed them in year 8 once you recognized that their chemical warfare activities (juglone) are limiting your ecological goals.
Post year 10: Seasoned and confident: You are a seasoned restoration practitioner now, an expert on your own land. Your management techniques are proven and efficient. You can spot and preempt potential issues before they become major time consumers. You recognize that scouting for invasive species and prescribed fire will be required management activities indefinitely. But unlike in the early years, this no longer scares you. Somewhere along your ecological restoration journey, you realized that it is not just you anymore. You against the continuous waves of enemy weeds. You are part of an army now. You stand shoulder to shoulder with your native plant and animal allies; working together to unlock the power of the oak savanna!