Embarking on Tree Research

July 14, 2021
Danie Frevola, a young white woman, points to a map in a forest as she conducts her research at Rowe Woods

by Laura Schmid, Membership Manager

One of the ethical concepts underlying the creation of Cincinnati Nature Center was the mindset proposed by Aldo Leopold in his famous Sand County Almanac. One of Leopold’s important points was that nature is not something that you go find at Land’s End or in the heart of the Amazon. Nature is thriving wherever you are right now—and nature is working 24-7 at Rowe Woods, with some very curious results. A land manager and a scientist have uncovered something of an ecological mystery, and they are branching out to find the answers.

Olivia Espinoza is the Nature Center’s Land Manager—and she is a certified Burn Boss. Since 2018, Olivia has conducted prescribed burns on our field habitats.

“Burning is such an important land management tool,” says Olivia. “Fire is used prescriptively for a variety of reasons. For example, in our fields, we use it to suppress nonnative species and boost the growth of native forbs and grasses.”

One thing Olivia and the land steward team noticed was our forests appeared to be maple-dominant.

What’s wrong with so many maples? Nothing, really. It’s just that land managers are keen to have oak-dominant woodlands because they provide so many benefits for wildlife. In fact, oaks support more life forms and species interactions than any other tree genus in North America.

In Ohio, more than 90 forest species eat acorns. Native oak trees also support over 550 species of caterpillars—a critical food source for songbirds.

Simply put, the oak tree may be one of the most essential members of the plant kingdom!

How do land managers achieve the result they prefer? In a woodland, prescribed burns have been used to promote an oak dominant ecosystem. New research suggests that without fire, woodlands can become more maple dominant. A century of fire suppression has contributed to fewer oaks in our forests, and land managers are now struggling to create conditions favorable for oak regeneration.

Olivia explains further, “Other variables are hurting oak regeneration, too, like climate change, invasives, and wildlife browse. In fact, deer and other wildlife tend to prefer oak saplings and seeds to maples, so that gives maples an advantage.”

There is much more to the problem. Some finicky invasive species like Amur Honeysuckle, Lonicera maackii, appear to be playing a contributory role. Amur Honeysuckle exhibits the characteristic of allelopathy, a genetic trait in which an organism actively doses the ground around it with toxic compounds to discourage competitor plants or consumption by animals.

Some think this allelopathic activity may be a contributing factor to oak suppression.

A couple of years ago, Olivia started to consider a woodland burn at Rowe Woods, but she didn’t have the data to back her intuition about the maple-rich forests.

Coincidentally, the Nature Center had just been awarded a generous three-year grant from the Charlotte R. Schmidlapp Fund, Fifth Third Bank, Trustee. This grant was earmarked to create a professional development and mentorship opportunity specifically for women interested in conservation and environmental careers. It was a perfect match, and Danie Frevola was hired as the Nature Center’s first Applied Conservation Apprentice.

She was subsequently tapped to census and develop the study of our old growth forest. The Nature Center’s conservation team has seen huge benefits since her arrival. Danie is originally from Cincinnati, and her academic career includes bachelor’s and graduate degrees from Northern Kentucky University and Ohio State University respectively, where she developed expertise in ornithology, wetland ecology, and invasive species biology.

After a couple stints in Hawaii and Montana, we were able to bring her back to her home roots. “We were looking for a strong female leader to help build a robust research program focused on land management,” says Director of Conservation Cory Christopher. “Danie was it!”

Since then, Danie has flourished and expanded her ecology prowess. “During my first year at the Nature Center, I focused primarily on learning land management skills. For example, I learned how to install prairies and several ways to manage invasive species. This year, I’m still doing a lot of land management, but now I’ve been able to dedicate time to research and our community science programs—like stream monitoring and butterfly monitoring. This past winter, I spent a fair amount of time compiling data, analyzing it, and sharing it back with our volunteer monitors.”

Shortly after joining the Nature Center, Danie started her woodland research. She set up plots using Geographic Information System (GIS) throughout our 43 acres of old-growth forest at Rowe Woods. “Old growth” means the forest has attained great age without significant human disturbance, and the plants, animals, and fungi in the area have “climaxed” in ecological natural succession.

Danie identified each tree in those areas by species and recorded their Diameter at Breast Height (DBH). DBH is a standard forestry metric, taken about 1.5 meters from the ground. After that, she examined the saplings in the area, counting all maples and oaks.

What came out of the census was this—across our old-growth forest, we have about ten times more maples than oaks. Danie’s findings created a baseline for further research, which is taking the form of a rather interesting experiment.

The Problem

Why do we have more maple trees than oak trees growing in our old-growth forest? What is affecting the overabundance of maple?

The Hypothesis

  1. Drought: Oaks are more drought tolerant. Weather data shows that we have a wetter climate today. Do maples thrive in our wetter climate?
  2. Amur Honeysuckle: Honeysuckles release allelopathic (toxic) compounds in their roots and leaves. Are maples more tolerant of the toxin?

The Experiment

In February 2021, Danie set up a common garden experiment in a hoop house located at our Long Branch Farm Nursery. “Common garden” is a generic term for the practice of examining and comparing variables under identical environmental conditions. Danie designed the experiment to expose the impact of two variables— drought and honeysuckle—on oak and maple trees.

First, Danie set up five tables of oak and maple saplings, all in random order. Next, Danie looked at historical weather data, which helped her determine how much water to give the trees. Certain pots then received different amounts of water and/or exposure to honeysuckle.

To accomplish the honeysuckle exposure, she collected honeysuckle leaves and soaked them in water. This allelopathic fortified “tea” simulated real-life exposure.

Danie started applying the drought and honeysuckle treatments on March 5, 2021. She’s been documenting germination date and growth rate, and the project is still ongoing. She plans to finalize and collect results this fall.

Later this summer, Danie intends to replicate another woodland census but in a different area where Olivia is contemplating a burn. After surveying the second area, the intention is to compare the baseline data from the old growth census to the second set of data.

“What we decide to do will depend on what the results tell us. We could decide to burn, or we may decide to thin trees or cut back honeysuckle. We are testing our hypotheses now through the common garden experiment,” says Danie. “Overall, the most important thing that will come out of this research is that we come up with a best research-based land management practice.”