NORTH CAROLINA—Land managers can now estimate the number of acorns in their forest each fall with methods devised by Southern Research Station scientist Cathryn H. Greenberg and her colleagues.

A forest's number of acorns can determine how fat deer get, which can influence where hunters choose to go.

Land managers for years stood or lay beneath oaks to estimate the number of acorns on the tree crowns. They categorized what they found by ranking, or indexing, crop years as excellent, good or poor. Because they used different methods, results couldn't be compared across a region.

Greenberg and collaborators knew there had to be a better, more efficient way. The scientists developed a standardized approach that takes much less time. Their 2020 study, published in The Wildlife Society Bulletin, builds on earlier studies that show how to best quantify acorn production for wildlife and forest management.

Crop sizes “fluctuate like crazy from year to year” and between oak species and locations, said Greenberg.

Using 21 years of acorn data, collaborators verified that when more trees are producing acorns, they're also producing more acorns per tree. That means land managers can rank their acorn crop simply by counting the number of oaks with acorns. This simpler method is called percentage-bearing-acorns.

Its results can be converted to the traditional index method, so land managers can still compare with past years.

The last piece of the puzzle explains how the PBA method can predict the number of acorns.

“It’s a more meaningful way to estimate acorn crop sizes, because it provides an estimate of actual quantities of acorns, rather than a general ranking of poor, good or excellent crop sizes,” Greenberg says.

Some forest planners are less interested in each year's crop size but want to know how many acorns their forests can potentially produce on average. In a related study, Greenberg and colleagues developed a way to model a forest's average acorn crop. They added their acorn averaging model into the Forest Vegetation Simulator—the growth-and-yield modeling system of the USDA Forest Service that virtually “grows” trees over time.

For a more thorough explanation, you can watch Greenberg explain the research in a PBS video.

For more information, email katie.greenberg@usda.gov.