Scientists at the University of Michigan are testing ways to make forests in the northern Lower Peninsula more resilient to climate change. About 12,000 mature trees, mostly aspen, are being cut down on 77 acres at the U-M Biological Station in Pellston and will be replaced with a mix of tree species and age groups that may be better equipped to handle climate and ecological changes.
The station spans 10,000 acres and is located just south of the Mackinac Bridge. The idea of the UMBS Adaptive Aspen Management Experiment is to replace some of the century-old aspen with the mix, which may be better suited to a warming climate, extreme weather events, and insect pests.
The harvesting started in March, paused in May for bird-nesting season and student summer research, and will be completed in September. By the time it’s done, about 200 truckloads of logs will have been hauled to a nearby mill for processing into wood siding and trim.
Cutting some of the mature aspen, which are nearing the end of their lives, will stimulate the regrowth of new aspen and should boost understory species.
“We’re reaching a point with our climate where we can’t pretend that it’s not changing,” says Luke Nave, project lead and ecologist and biogeochemist at U-M. “To sit by and do nothing, when we have a forest that is vulnerable to climate change, would be irresponsible.”
Aspen in the Great Lakes region are considered “climate change losers,” says Nave, and are not expected to fare well as the area warms up. Forests dominated by a single species and containing trees of a uniform age and height may be especially vulnerable.
“I’m not a finance guy, but you can think of forest management in terms of investment strategies,” says Nave, who is also an associate research scientist at the Biological Station and in the U-M Department of Ecology and Evolutionary Biology. “You don’t put all your investments in one place. You try to diversify, because it protects you against risk. So, if you have different tree species arrayed in different age classes across the forest, that’s a diversified investment strategy that increases your capacity to respond to climate warming, drought, and severe weather events.”
The project is the demonstration site of the Northwoods Climate Change Response Framework, a regional collaboration among scientists, land managers, and private landowners to advance climate change adaptation efforts.
A 2014 forest vulnerability assessment by the Framework concluded that suitable habitat for aspen in northern Michigan will sharply decline by the end of this century if little is done to rein in global emissions of heat-trapping greenhouse gases.
The project involves a $178,000 timber sale to Louisiana-Pacific Corp., which operates a mill in Newberry in the eastern Upper Peninsula and employs 127 people. The mill makes LP SmartSide siding and trim, one of the company’s best-selling products.
The sale is expected to yield 8,600 tons of wood – 7,700 tons of aspen plus other hardwoods and some pine, according to Travis Kangas, a resource manager for Louisiana-Pacific.
The cutting is being done at a Biological Station site known as the Pellston Hill. Three management studies are being tested on the harvested trees’ home in four sections.
The transition treatment aims to quickly move the forest away from mature-aspen dominance toward more diverse cover types by cutting mature aspens and leaving longer-lived species such as red oak, sugar maple, red maple, striped maple, yellow birch, paper birch, ironwood, basswood, hemlock, red pine, jack pine, white pine, and balsam fir. American beech, which is in a severe, disease-driven decline across much of the state, is also present at the site. Individuals without the disease will be studied to see whether they are naturally resistant to their insect and fungal pathogens.
The resistance treatment will attempt to retain aspen and birch in a location that’s cool, shady, and moist with north-facing slopes and a high groundwater table. The factors could enable trees on this unit to resist climate change-driven drought and heat. Nearly all of the saleable trees will be removed with the intent of regenerating a mix of aspen and birch.
Two resilience treatments seek to maintain aspen stands in the future but to increase diversity of species, age classes, and stand structure. Most of the mature aspen will be removed while most of the understory trees will be retained, including red oak, red maple, beeches without diseases, and some red and white pines.
The 77-acre harvesting zone is within a 452-acre management area that includes untreated reference areas and several young stands that regenerated after being clear-cut in the early 1970s or 1980s.
“The forestry community is still very early in the process of learning what it means to adapt to climate change. So, demonstration projects like this will provide really useful information that will help the whole community learn about climate adaptation,” says Stephen Handler, a climate change specialist with the U.S. Forest Service in Houghton, Michigan, who also works for the Northern Institute of Applied Climate Science.
Revenue from the timber sale will fund a study of tree-harvesting impacts on groundwater and soil carbon throughout the management area. Proceeds from the sale will pay for the installation of groundwater monitoring wells and analysis of thousands of soil and groundwater samples collected from the wells.
Kangas says he was impressed by the amount of usable timber and its market value in the forest.
“This is a high-quality site for aspen,” he says. “I couldn’t believe the size and volume of the trees when I first cruised it. You see aspen like this in Canada, but you just don’t see it in Michigan.”
Once aspen trees are cut, the remaining roots send up new “suckers,” or tiny trees, to replace them. Most will die as they compete for resources, but enough survive to recreate the forest under the right conditions.
The aspen now nearing the end of their lifetime at the Biological Station were established following the logging and wildfire disturbances that transformed the forests of the Upper Great Lakes region more than a century ago. Most of the aspen there now date from between 1908 and 1919. The station was established in 1909, and generations of researchers there have been studying the forest’s recovery.
A report issued by the Framework in 2014 examined a high-emissions climate change scenario, which authors predict is more realistic, and a lower-emissions scenario. The high-emissions scenario projects an 11.2-degree Fahrenheit summer temperature increase in the assessment area by the end of the 21st century, and summer precipitation is projected to decline by 3.8 inches. Under both scenarios, winters are expected to continue warming faster than other seasons, and snowfall totals are projected to decline as more precipitation falls as rain.
Nave says it could take a decade or more to know which aspen-management treatment is most effective.