Planting oaks: a recipe for success

One-year-old northern red oak seedlings growing in nursery beds at the East Tennessee State Nursery near Delano, TN. USDA Forest Service photo by Stacy Clark.

Growing oak trees to maturity begins with two ingredients: viable acorns and competitive seedlings. USDA Forest Service scientist Stacy Clark wrote a cookbook to help managers with the regeneration process in healthy, productive oak forests.

To regenerate an oak forest, healthy, large oak seedlings and saplings must be present in the understory before overstory trees are removed. This regeneration layer is often lacking, especially in the Southern Appalachians.

It is the hope that tips from these guidelines will help national forest managers and landowners supplement the natural oak regeneration layer with planted seedlings so that they can successfully compete and grow a new generation of oak forests where it may be desired.

Clark and collaborators from the University of Tennessee’s Tree Improvement Program and the Southern Region of the National Forest System have been working together for the last 16 years as part of a decades long partnership. They wrote these guidelines specifically for national forest silviculturists and foresters — but any landowner or forester who wants to regenerate upland oak through planting will find nuggets of wisdom between the pages.

For example, if you collect your own acorns, start the process a year and a half before the planting. Be prepared to collect three times as many as you need: up to 30% of the acorns will be lost due to poor germination and another 40-60% will be discarded during seedling grading. Only seedlings above a certain size threshold and with a well-developed root structure should be planted. This improves seedling survival and growth.

Collecting locally-sourced acorns ensures that seedlings have the genetic adaptations best suited for the conditions where they will be planted. For example, acorns collected in the Pisgah National Forest of North Carolina should be replanted in the Blue Ridge Mountain region, not the Coastal Plain of northern Mississippi. Acorns collected from high elevation forests (above 4,000 feet) have evolved traits to survive well at that altitude and thus should be replanted there.

Variable sizes of one-year-old bareroot nursery seedlings of northern red oak, from lowest quality on the left to highest quality on the right. USDA Forest Service photo by Stacy Clark.

“It’s a good idea to collect acorns from a variety of trees spaced at least a quarter mile apart to increase the genetic diversity of your crop,” says Clark. “We have found that genetics affect nursery seedling quality and planting outcomes.” Remember the float test! Discard the acorns that float, because they are more likely to be insect damaged or desiccated.

Planting oak seedlings correctly is critical to their survival, growth, and competitiveness. Another key message from the guide: do not let the roots dry out. Shorten the time between lifting seedlings from the nursery and planting them, use the proper planting tools, make sure the root collar is flush with the ground, and distribute the largest seedlings evenly across the planting area. “Another tip is to plant the best quality seedlings in areas that have the most competition or where early seed production is desired,” notes Clark.

The Southern Region has many active seed orchards, including the Watauga Northern Red Oak Seed Orchard, the oldest northern red oak orchard in the country, established in 1974. It is in full production and managed by University of Tennessee’s Tree Improvement Program to provide high quality oak seedings to Ranger Districts across the Southeast. They have supplied experimental material for many of Clark and colleagues’ research projects.

Read the oak planting guidelines in this General Technical Report.

For more information, email Stacy Clark at stacy.l.clark@usda.gov.

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