Study: Today’s forests less diverse, trees younger

Catherine Thomas

America’s landscapes, once replete with lush forests, are not what they used to be.

So concludes a recent study by a team of researchers led by Lisa Schulte, assistant professor of natural resources ecology and management. Comparing forest composition data from the mid-1800s to today’s forests, the researchers concluded that heavily harvested forests in Minnesota, Wisconsin and Michigan have younger, smaller trees and lack the diversity of the forests of years past.

“There was a period around the 1900s when there was a lot of deforestation, particularly in northern Minnesota, Wisconsin and Michigan,” said Laura Merrick, assistant director for undergraduate research and scholarship in the University Honors Program, which contributed to the study. “During a period of about 60 years, some 2 million acres of forest were harvested or cleared for human settlement.”

After this clearing, fires often ravaged the forests, Merrick said.

“That was followed by periods of intense fires – some the result of natural causes and some deliberate,” Merrick said. “Removing and discarding unwanted material from harvested trees, known as slashing, fueled these wildfires; the intense heat generated by the fires destroyed vital nutrients in the soil, preventing the forest’s regeneration.”

During the time of the early American settlers, continual timber harvesting harmed the ecosystem, Schulte said. Trees were not allowed to regenerate because mature trees were cut down during this time, she said.

Schulte said ramifications from deforestation in North America can still be felt today.

“One of the biggest contributors to global climate change is land use conversion,” Schulte said. “When you cut down a forest and till the soil, you release a whole lot of carbon into the atmosphere. We feel the effects, today, of these conversions from the past.”The study also tracked changes in forest composition, or diversity. Several species of trees have been lost to the nation’s forests.

Lost species are often grown for harvesting on plantations, which are essentially row after row of the same species, Merrick said.

“Diversity in our forests has dramatically decreased over time,” Merrick said.

Schulte also said economic motives influence the diversity, or lack thereof, of America’s, and the world’s, forests.

An estimated 2 percent of the world’s remaining forests are being harvested every year. It is generally acknowledged that problems associated with deforestation include a loss of species habitats, species extinction, flooding due largely to topsoil erosion and changes in the amount of carbon dioxide in the atmosphere, Schulte said.

“Timber harvesting does not have to be harmful to the ecosystem,” Schulte said. “New techniques have been developed that allow us to harvest timber from forests in a matter that is ecologically sensitive.”