From an Acorn

Now, thanks to studies by Loftis, earlier researchers at the Bent Creek Experimental Forest, and many other researchers in the East, we have a much better understanding of the oak regeneration process. The first and most important point is that upland oaks, as a group, will only be present in a new stand if competitive oak regeneration sources were present in the previous stand and persist through the disturbance—in this case, harvest. In its simplest form, the process involves three elements:

1. Establishment of new oak seedlings in an existing stand following a good acorn crop
2. Development of those seedlings in the existing stand into regeneration sources that can compete successfully when released
3. Timely and sufficient release from overstory competition

For oaks to regenerate, all three elements must occur in sequence and within a certain time frame. On many sites in the Southern Appalachians and beyond, the lack of oak regeneration appears to result from the failure of the second element—the development of seedlings into competitive regeneration sources—to occur.

“My colleague, retired research forester Paul Johnson with the North Central Research Station (NRS), literally wrote the book on oak ecology and silviculture,” says Loftis. “He suggested that on some very dry sites, development of competitive oak regeneration sources can occur without disturbance, because stand conditions are typically sparse enough to provide enough light for seedling development. Paul coined the term accumulator systems to describe this.”

But on most other sites, oak seedlings will not develop sufficiently to be able to compete with yellowpoplar and other species after release without some sort of stand disturbance that alters the light regime in just the right way and for a sufficient amount of time prior to release.

In the Southern Appalachians, very shady conditions under mature stands lead to substantial oak seedling mortality and little growth of the surviving oak seedlings. Treatments that provide too much light, while encouraging the growth of oak seedlings, also promote the establishment and development of competitors such as yellow-poplar.

Part of Loftis’ research has involved finding a stand treatment that provides the light necessary for oaks to grow, but retards the establishment and development of yellow-poplar. The treatment resulting from this research, sometimes called an oak shelterwood, leaves the main canopy intact but removes much of the vegetation between the main canopy and the ground. After 10 years or so, the small seedlings that had become established as a result of a good acorn crop have developed into much larger seedlings—the regeneration source—now capable of competing after release.

Cross-Region Ambitions

Attendants at a recent SRS All Scientists meeting talked about the possibility of a future cross-regional oak regeneration study. “The objective of the study we are planning is to test oak regeneration prescriptions across upland hardwood forests in the South, and to determine which prescriptions work and where, with a specific focus on the moisture gradient,” says Loftis. “Managers need this information to plan appropriate treatments where the regeneration and maintenance of oak ecosystems helps meet their management objectives.”

Loftis commented that some suggested prescriptions for regenerating oak include the use of prescribed fire. “Some people suggest that merely ‘returning fire to the ecosystem’ will ultimately restore and maintain oak ecosystems, or ecosystems where oak is an important component. Pat Brose (NRS) and Dave Van Lear (Clemson University) developed a much more specific prescription for the use of fire in oak regeneration. I developed a method that does not include the use of fire and seems to be applicable to higher quality sites.”

REGENerating More than Oak

Another component of Loftis’ research involves the development of regeneration prediction models. His early work focused on predicting the amount of oak that might be expected, if, at a given point in time, an existing stand were regenerated, based on the oak regeneration sources that already existed in that stand.

“The first step in oak regeneration is to assess the adequacy of oak regeneration sources that are present in the existing mature stand where regeneration is contemplated,” says Loftis. “Only then will we be able to compare the amount of oak desired in the new stand with what we would expect based on the prediction.”

In his more recent work, Loftis has attempted to develop a more general regeneration model.

“I began to think about a general regeneration prediction model in the early to mid-1980s. It is, in some ways, an extension of my work in oak regeneration and the model I developed to assess oak regeneration potential in the Southern Appalachians.”

“The earlier model predicts the amount of oak to be expected in a new stand given the oak regeneration sources that are present in the existing mature stand. But on moist sites that support many species, we need a model that predicts species composition—not just the amount of a single species group.”

The newer model, a hybrid that includes both an expert systems component and inputs from empirical models, was designed with regeneration harvests in mind, but could be applied to other stand replacing disturbances such as wildfires and major weather events. Known as REGEN, the program that implements the model predicts species composition of a new stand created by substantial overstory removal.

While REGEN was developed for the Southern Appalachian region, it can be adapted for use across most ecosystems and tree species.

“The REGEN program is designed to be modified or calibrated for other areas or ecosystems—wherever the underlying concepts seem to provide a reasonable model of the process, and where scientists and managers feel they have enough information to drive the model,” Loftis says. “Currently, a version for western Virginia has been calibrated by Tom Fox at Virginia Tech and for the northern Cumberland Plateau by Jeff Stringer at the University of Kentucky. Within our own unit, Callie Schweitzer has been collecting research data for several years that will provide very important information for calibrating and refining the version for the Cumberland Plateau.”

In early June, Loftis announced plans to step down from the project leader position to return his focus to regeneration research, effective this fall.

“I will be attempting to do a synthesis of our older regeneration studies, then use that synthesis to explain the working hypothesis for my regeneration model implemented by the REGEN program. And I will be using some newer data from plots I installed in the 1990s to test and refine REGEN,” he wrote in a letter to colleagues.