Study: Some tree species unable to adapt to climate change
Many trees common in forests across the eastern U.S., including Minnesota and Wisconsin, won't be able to keep up with the current pace of climate change, according to a new study by the Woods Hole Research Center.
The study echoes the findings of other, recent scientific research that shows some northern tree species simply won't adapt fast enough to climate change that scientists say already is occurring.
The most recent study, published in the journal Global Change Biology, looked at 40 different eastern U.S. forest species and found balsam fir, quaking aspen and red spruce among the most vulnerable species to warming temperatures.
The trees will begin to fail in warmer climates in many areas and won't keep up with changes without human intervention, according to the study's conclusions.
"Trees, after all, cannot walk," said Woods Hole scientist Brendan Rogers, the study's lead author, in a statement with the study's release. "They must disperse seeds that, in turn, establish, grow and reproduce. The pace of climate change threatens to rapidly overtake this migration, and landscapes fragmented by humans present even more challenges."
The study was intended to help managers of U.S. national parks decide if and when to intervene to preserve traditional species in their areas, including actively assisting tree species migration by planting. That flies against traditional National Park Service policy of letting nature take its course. The study suggests that even if suitable conditions for a species are predicted to expand in a specific area, human development has often fragmented forest habitat to block that species' ability to disperse seeds and expand its range.
Lee Frelich, director of the University of Minnesota's Center for Forest Ecology, who was not involved in the Woods Hole study, said its modeling appears to have oversimplified impacts because researchers used such a huge geographic area of the country for their modeling. Species will react differently to climate in sub-regions, he noted.
But Frelich said the end results mesh well with several other studies.
"Northern species are going to be the hardest hit. They already are," Frelich said.
Because northern Minnesota summers already have warmed a couple degrees on average, Frelich said, red maples have started spreading across forests once dominated by spruce and fir, echoing findings that a small change in temperature can determine what species thrive and which fade away. Frelich predicted this in studies published in 2012 and 2013.
"Red maples are expanding explosively across the Boundary Waters right now; they are showing up everywhere," he said, noting red maple has an advantage over other warmer climate species because their seeds are light and carry farther in the wind.
Frelich has been a proponent of human intervention for a decade or more to prevent iconic areas like the Boundary Waters Canoe Area Wilderness from eventually becoming oak savannas, the next cycle Frelich predicts for the area when temperatures get too warm for red maples.
"We know white pines can handle warmer temperatures because we know they can thrive in southeastern MInnesota. But will we need to move those southern ecotypes north? Or will the Boundary Waters white pines be able to adapt?" Frelich said.
Southern Minnesota white pines will never move fast enough north on their own to fill in up north, he noted, and could never spread their cones across fragmented areas where farms and urban landscapes block their path.
Frelich said the changes aren't just impacting trees, but also shrubs, flowers and even the pollinators that allow plants to thrive.
"We need to know how whole systems are going to change to keep up, or not change, as this happens," he said. "If anything, I think the pace of this changeover is speeding up."
The Massachusetts-based Woods Hole study is at least the third major study in recent years that warns species like fir and spruce may be in trouble as climate change continues.
In January, 2015, researchers at the University of Minnesota published a report in the journal Nature Climate Change that used growing plots near Cloquet and Ely and added the amount of warmth expected later this century. The study was the first of its kind in a northern forest to use ceramic heaters to warm the air near newly planted seedlings as well as heating cables in the ground.
Spruce and fir, which thrive in cooler areas, suffered poorer growth and survival when warmed just a few degrees — up to a 40 percent decline in growth. The study compared trees exposed to the actual temperature over three growing seasons to trees that were exposed to temperatures 3 degrees Fahrenheit above the actual air temperature, and other trees that got a nearly 6 degree warmup. That's the warming range climate scientists say we can expect by the end of the century if climate change continues at the current pace.
And a study released in June 2014 by the U.S. Forest Service Northern Research Station that looked at 23.5 million acres of forest across northern Minnesota described both the effects of climate change that have already been observed as well as projections on what continued warming is expected to do.
The findings were that trees already at the southern end of their range will do poorly — including balsam fir, aspen, white spruce and tamarack. That study suggested tree species at the northern edge of their range will do better — including basswood, black cherry, white pine, red maple, sugar maple and white oak. Researchers said the evidence suggests the climate is changing much faster than ever before, and that tree species on their own can't migrate or adapt fast enough to catch up.