The history of a forest might be measured by the trunks and branches looming overhead. But for some MSU researchers, a forest’s future lies in what’s growing under their feet.
Every summer for nearly three decades, a team led by Ecology, Evolution and Behavior core faculty member Richard Kobe has made its way to Manistee National Forest in northwestern Lower Michigan to look for new trees that have sprouted.
At less than a year old, the youngest seedlings growing in the understory aren’t much taller than their toes.
But now, the team’s annual counts of 10 common tree species are starting to reveal clues to what the region’s forests might look like in the 20, 40 or 100 years to come.
That’s no small matter in Michigan, where forests cover half the state, supporting more than 90,000 jobs and adding $27 billion to the economy each year.
Forests are more than just scenic recreation areas; they also filter air and water, prevent erosion, provide timber and serve as habitat for other species.
But forces of change, from insect outbreaks to shifting weather patterns, are testing their resilience. Average temperatures in the Great Lakes region have risen by 2.3 degrees Fahrenheit since the 1950s, and they are projected to increase by 6 to 11 degrees Fahrenheit by the end of the century.
As temperature and precipitation patterns shift, the researchers are finding that some seedlings are better suited than others to the climate that’s around them.
In the life of a tree, the young seedling stage is a critical time, said study co-author Bailey McNichol, a postdoctoral scholar in the Kobe lab and in MSU’s Ecology, Evolution and Behavior program.
Seedlings are more sensitive to warming and drying due to their shallower roots. “This is also the stage when trees are most at risk from diseases and grazing deer,” McNichol added.
“It’s the point in a tree's life when it has passed the first series of gauntlets — it’s made it through germination and it's starting to sprout — but it still has a long way to go,” McNichol said.
Many seedlings won’t make it. But over time, some will become the next generation, eventually taking over as older canopy trees die out.
In a new study published in Global Change Biology Communications, McNichol and Kobe compared years of seedling data collected at 12 sites spread across a 370-square-mile area in Michigan’s Manistee National Forest.
At each site, researchers walked a transect and counted and identified each tree seedling less than one year old. Many seedlings consisted of little more than a wisp of a stem and a pair of leaves. Some, like maples, were easily identified by their jagged edges or sunken veins. Others required a more discerning eye.
The researchers have been returning to the same sites every summer for 25 years now. In that time they’ve catalogued some 188,821 seedlings. Along the way, they also recorded the air temperature, soil moisture and fertility and how much light reached the forest floor.
The relationships between these variables and seedling abundances suggest that, in Michigan’s northern forests, some tree species will continue to thrive in the warmer, wetter decades to come — including white oak, red oak, black cherry, red maple and ironwood.
But other species — such as sugar maple, American beech, white ash, basswood and black oak — may no longer be able to make it in the places they once did.
“These species might become less common in Michigan's forests in the future,” McNichol said.
Tree canopy cover can help shelter some species from the effects of climate extremes, by creating cooler and moister conditions for the seedlings below, the researchers found.
But shifting climate won’t be the only obstacle these trees face, McNichol said. Even if they make it past the perils of early life, they’ll need another few decades before they’re able to bear seed. In that time they could also succumb to diseases, pest outbreaks or damage from hungry deer.
To better predict the future trajectory of the forest, next the researchers plan to track tree survival after the first year, to determine which ones make it to the sapling stage and beyond.
“The idea is to tease out factors that don’t just influence where tree seedlings show up, but how long they stick around,” McNichol said.
This research was supported by Michigan AgBioResearch at Michigan State University, and the National Science Foundation.
This story was originally featured on the Ecology, Evolution and Behavior website.
