Greenmatters

Greenmatters

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Tending Trees for Science

When horticulturists tend flowers or prune shrubs in the Grand Garden or Arbor Court at The Morton Arboretum, their goal is to grow beautiful plants for the enjoyment of guests. Jonathan Steele’s goal is different: to grow plants to serve science.

As the research horticulturist in the Center for Tree Science, he cares for living experiments. He is helping to answer scientific questions that are crucial to the future of trees and people.

The scientific goal makes a big difference in how he cares for the plants, from breeze-blown prairie flowers to 20-foot-tall trees. “In an experiment, we want to make sure that everything is constant among the plants except for the variable we’re studying,” Steele said.

For example, in a study testing whether a waste product from growing mushrooms might be useful as a soil amendment for urban trees, he has to make sure that all other factors, such as water and mulch, are held the same between the trees whose soil was amended and the untreated control trees.

Steele worked at a variety of landscaping and horticulture jobs, including at a college and a zoo, for more than 10 years, developing an interest in “the intersection of the built environment and the natural world.” When he spotted the Arboretum’s job listing three years ago for a research horticulturist, “I was intrigued, because I’d never seen that before,” he said. He became one of only a handful of people who have that role at U.S. institutions.

“The dual skill set that Jonathan has is very important,” said Meghan Midgley, director of the Center for Tree Science. “He has both an understanding of the research questions we’re trying to address, and the horticultural skill to care for the trees and plants.”

Steele works on multiple projects simultaneously, both in the research greenhouses attached to the Administration and Research Center and in Ware Field, the nonpublic acreage in the northwest corner of the Arboretum that is dedicated to research. In his work for the Arboretum’s Center for Tree Science, he collaborates with the Arboretum’s highly skilled Collections and Horticulture and Natural Resources staff. “What can be tricky for me can be easy for them,” he says. “We have tremendous resources.”

Much of his work is routine: watering, repotting, weeding, mowing around trees, maintaining the mulch over their roots. As he tends the plants, he is watching for changes that may be relevant to a study question. Meanwhile, he works with Arboretum scientists as they design new experiments.

In the greenhouses, Steele tends seedlings and saplings for scientists studying disease resistance, genetic diversity, and other topics. Outdoors, he cares for an experimental plot of prairie plants, a group of bur oak saplings, and one of the Arboretum’s most distinctive and ambitious undertakings: a large planting of trees intended for arboriculture research.

Scientists need trees to experiment on to test the effects of tree-care practices and environmental conditions. For example, to study the long-term effects of different pruning techniques, researchers need to try them out on living trees and then watch the trees for years to see how they respond. To learn how much force from stormy winds or heavy ice it takes to bring down tree branches, scientists need to break the branches of real trees.

The arboriculture plantings in Ware Field are intended to provide a supply of trees for that kind of research, carefully selected and documented throughout their lives so they make useful experimental subjects. “We have great data on the trees in the Arboretum’s collections,” Steele said, “but nobody wants to break those trees.”

Establishing an inventory of trees for future research is a farsighted, long-term investment that only a well-supported institution such as the Arboretum could make. Many botanists experiment on quick-to-grow green plants such as Arabidopsis, which has a lifespan of about six weeks. Trees have a lifespan of decades. Planted today, they may not reach a useful experimental size until some of today’s scientists have retired.

“We’re planting those trees now so that 30 years from now, somebody will be able to come in and use them to ask innovative questions about arboricultural practices,” Midgley said.

Some of the older trees—spaced out in wide rows, like a huge cornfield—are already 15 to 20 feet tall. In the last few years, Steele has helped plant about 300 more trees of species often used in urban sites. The tree plot includes bur oak (Quercus macrocarpa), swamp white oak (Quercus bicolor), and shagbark hickory (Carya ovata). “We’re trying to get data that apply to urban trees as they are normally selected, planted, and maintained,” he said. There is room to plant more if resources are available.

In the experimental prairie plot nearby, Steele has to control weeds carefully without harming the native plants or interfering with the way they reseed, since the way the plants compete and redistribute themselves is important to the study.

The challenges are different for the bur oak common garden plot, a study comparing the growth of young trees at the Arboretum and other sites in Minnesota and Oklahoma. To make sure that the trees in all three sites are treated the same, he constantly confers with the growers in the other states.

Steele is proud to be using his knowledge, skills, and experience to contribute to the Arboretum’s research program. “This is an institution that really cares about research and about doing it well,” he said. “There’s a lot of ambition in the science that is practiced here.”