Department of Biology

Small team spends summer conducting 'tree census' on IU-owned land deep within one of the state's oldest forests as part of global research project

A small team of Indiana University researchers took on a seemingly insurmountable task this summer: physically measuring the size and location of every tree in 62 acres of land deep within one of the state's oldest forests.

The site of the project is Lilly-Dickey Woods, part of the IU Research and Teaching Preserve in Brown County, Indiana, and one of only 51 plots of land in the ForestGEO network—a global network of forests whose study is funded by the Smithsonian Institution to advance knowledge about how trees grow and react to changes in the environment. The site is also one of only several forests in the network in the Midwest, providing vital data about how environmental change impacts forests in the central U.S.

"We've never bothered to count how many trees we're going through every day; we're all just working so breathlessly," said Mark Sheehan, a technician in the IU Bloomington College of Arts and Sciences' Department of Biology, who leads the four-person team tasked with measuring nearly 30,000 trees in three months. "Some days it goes fast; other days you're crawling on your hands and knees under a dense thicket of pawpaw trees."

The remoteness of the forest is a challenge. Located about 45 minutes outside Bloomington in the heart of one of the few old-growth forests in the state, the worksite requires hiking nearly a mile into the deep woods—or a bumpy jeep ride down a log-strewn dirt road. Another challenge is weather and wildlife: Temperatures regularly rose into the 90s this summer, and insects such as yellow jackets—a swarm of which temporarily sidelined a crew member with multiple stings—posed a threat.

Yet Sheehan said it's rare that anyone mentions the hard work or the heat. "Honestly," he said, "we all feel privileged to spend every day working out in nature."

Nor is this the first time that IU researchers have tackled the herculean task. This year's project is a follow-up to the first "tree census" conducted on the site over five years ago. The differences in tree growth and deaths between then and now reveal vital information about tree species on the rise or fall in Indiana.

That first tree census was completed over the course of three months in 2012. This year's task is also a three-month job, although project leaders note that if a single person were to attempt it, the census could easily require a year.

In addition to Sheehan, IU scientists on the project are graduate student Carson Hoogewerf and forest ecology technicians Matthias Gaffney and Aubree Keurajian, who joined IU for the summer to participate in the project. IU faculty members involved in the effort are Richard Phillips, professor in the Department of Biology and director of the IU Research and Teaching Preserve, and Keith Clay, an IU Distinguished Professor who served as director of the preserve from 2002 to 2014. The initial tree census was led by then-IU Ph.D. student Dan Johnson, who returned this summer for part of the project.

"The long-term collection of data from forests across the globe is incredibly important to scientists studying the impact of changing temperatures and carbon dioxide levels on the environment," Phillips said. "You can't prove that something has changed if you're missing baseline data to compare your observations against."

The project also recently marked a major milestone: the publication of the first study to draw upon data from multiple sites in the ForestGEO network. Clay, Phillips and Johnson are among the co-authors on the paper in the internationally acclaimed journal Science.

By analyzing more than 3,000 species and nearly 2.4 million trees in 24 forest plots worldwide, the study found that trees growing in areas with a high concentration of the same species fare poorly compared to trees growing in areas with a greater diversity of species. The paper also reported that this effect persists across both tropical and temperate forests—although a strong diversity of species appears especially important in cooler forests in countries such as the U.S. and Canada.

"This study shows that the dense aggregation of similar tree species is unhealthy due to factors such as the transmission of pathogens from older to younger trees through root networks," Clay said. "Basically, plants do better in their 'neighbor's' soil."

The findings demonstrate how the loss of tree species can harm forests, especially in temperate zones with less diversity. Lilly-Dickey Woods has about 36 tree species, for example. A tropical forest, by contrast, can easily contain over 400.

For the team working in Brown County, Sheehan said the forest's complex lifecycle is written in the landscape. Small saplings in sun-dappled patches of dirt stretch toward the light beside fallen forest giants whose collapse only recently freed the younger trees to grow. The loss of the older trees is due partly to the natural cycle of life and death, but also to environmental factors such as the invasion of the tree-killing emerald ash borer and a major statewide drought in 2012.

The meticulous collection of data from the woods empowers scientists to untangle the impact that these and other factors have on the forest in Indiana, Phillips said. It will also reveal the diversity of the forest's species, shedding light on larger trends in forest health across the state and the world.

Lastly, Clay added that none of the research in Lilly-Dickey Woods could take place without a generous gift to the university 75 years ago. Two Brown County neighbors—J.K. Lilly, a scion of the Indiana pharmaceutical manufacturer Eli Lilly and Co., and Marcus Dickey, the personal secretary and biographer of Indiana poet James Whitcomb Riley—donated adjacent plots of land to then-IU Chancellor Herman B Wells in 1942 with the promise that the forest remain in a natural state for use in art and biological research.

IU's careful stewardship of the land over the past 75 years and, more recently, the inclusion of the woods in a global project to understand the impact of environmental change on our planet is a powerful testament to the endurance of this agreement, Clay said.

This year's tree census at Lilly-Dickey Woods was completed in September.