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Peter Reich
Forests in the 21st century could look very different than the forests we now have in northern Minnesota.
That’s the news from a story recently published in Nature.
In the coming years warming temperatures alone could cause nine northern conifers in Minnesota’s Northwoods and southern boreal forest running from eastern Canada to Alaska to be replaced by oaks and maples, reports a study released by the Department of Forest Resources at the University of Minnesota.
Said to be a five-year study (it was longer) it was led by Peter Reich, a Department of Forest Resources professor at the University of Minnesota. Reich and fellow researchers used infrared lamps and soil heating cables to warm more than 4,500 seedlings and saplings on two sites, one in Ely and one in Cloquet.
Researchers warmed the seedlings around the clock from early spring to late fall using two different levels of potential 21st century temperatures, one at 1.6C (2.9 F) and 3.1 C (5.6F above current ambient temperatures, varying those from hour-to-hour and day to day. Precipitation shifts were also studied by using moveable tarps to capture rainwater on some plots before the water reached the plants and soil. Included in the study was a control group of trees grown at ambient temperatures and moisture levels.
What the researchers discovered was alarming.
“Present-day southern boreal forest may reach a tipping point with even modest climate warming, resulting in a major shift in the kinds of species present, and with potential adverse impacts on the health and diversity of our forests,” said Reich. “Those impacts could reduce the capacity of our forests to produce timber, host other plant, microbial and animal diversity, dampen flooding and perhaps most important of all, scrub carbon out of the air and hold it in wood and soil.”
While oaks and maples may replace the trees we now have, the study says they will unlikely fill the void left by the vanishing conifers.
Who is Peter Reich?
Reich graduated with a Ph.D., in 1983 from Cornell University. He is Regents Professor, Distinguished McKnight University Professor, and F.B. Hubachek, Sr. Chair in Forest Ecology and Tree Physiology. His work includes studying the effects of rising CO 2 and associated climate change on biodiversity loss, and wildfire. The day I read the report I reached out to Peter to ask some questions and lickety-split, he returned some interesting, thoughtful answers.
Q- What were the variety of trees used in the study?
This was one five-year experiment within what is now a 14-year project. We used white spruce, balsam fir, paper birch, jack pine, white pine, red oak, bur oak, sugar maple and red maple in this 5-year study (we also planted trembling aspen, but the seedlings were of poor quality and did not survive in any of the treatments so were not included in the results). Over the 14 years we’ve now got results for those 10 species plus at least another dozen – almost all of the tree species important in the state.
Q- How much did it cost and how many people helped?
We’ve been lucky to get grants from the National Science Foundation and the US Dept of Energy to fund the experiment, which costs roughly $400,000 per year to run. The University of Minnesota and the Minnesota Invasive Terrestrial Plants and Pests Center have also helped fund the work (the latter to support examining whether buckthorn and honeysuckle will invade the Northwoods more effectively in a warmer world). Each spring through fall teams of roughly 12-15 people (undergraduate students, technicians, graduate students, postdoctoral researchers and faculty) are involved in keeping the experiment happening and making all of the measurements on site.
Q- If the 21st century temperatures reach 2.9 F or 5.6 F in the northland ,will we lose our birch and poplar trees?
Great question! We found the negative effects of warming in our experiment were almost all related to increased soil water deficits caused by greater water loss from warmed plants and soils. So, the extreme sensitivity of spruce and fir and the more modest sensitivity of birch and poplar are largely a response to increase water stress (low soil moisture) not to the slightly higher temperatures per se. One of the most dramatic responses we highlight in our current paper is the response of paper birch. In wet conditions, it thrived at higher temperatures and grew much much faster in warmed than control temperatures. But in drier conditions it grew much much slower in warmed than control temperatures. So, its response to rising temperature was entirely dependent on how moist the soil was.
Projections for future climate are that we will see more precipitation in the spring and early summer, but with more run-off when that rain falls in deluges means less gets into the soil; and projections are for similar or less rain in mid and late summers twenty or more years from now. We need 7% more rain with every 1 degree C rise in temperature simply to keep pace with higher water loss from transpiration and evaporation. So, our forests will likely experience more wet springs and more dry summers in the future. If enough of those summers are warm and dry we could well lose a lot of our birch and poplar.
Q- How will our thin soil host oak trees?
Another great question! Sugar maple and oak as seedlings in our studies could handle warmer, drier conditions than spruce, fir, pine and birch; but wherever soils are thin, that will provide a real stress test for even the oaks and maples. In summer 2021 I saw young and mature maples and other hardwoods on the North Shore and inland wilting and losing browned leaves due to the drought, especially on thin soils. So, even if oaks manage to colonize on thin soils, they are not going to grow as fast or be as resilient as an oak on a deeper, richer soil.
Q- Without proper cover streams will warm too much for brook trout. Moose will be long gone. Lynx as well. And bird species common to our area will move to colder climes.
All of this is accurate.
Q- None of this will affect either you or me, right?
Well here, unfortunately, this might not be true even for us!
Q- So, I read your brief profile online and you note it is easier to ask questions than come up with answers. Of course, questions and research are essential to getting to answers, so I was wondering if there are proposals to making the nine potentially affected tree species more resistant to warming? Or is this too early/late to ask this question?
Another great question! There is a lot of talk about doing exactly this. One way is to move seeds (or seedlings) from warmer drier parts of the species ranges and plant them in northeastern MN. All fir or maple (or any other species) are not identical genetically and not surprisingly those from drier warmer parts of their geographic range have adaptations that make them cope better with warm dry conditions. Two problems here. For some species like spruce and fir, northern MN is already at their warm dry range edge so there aren’t ecotypes better adapted to even warmer, drier conditions. For others, like aspen or birch or oaks and maples (or species non-native to the boreal forest like hickories), the problem is we can’t economically afford to seed or plant large areas with genotypes from elsewhere. And they won’t be able to migrate on their own rapidly either.
Q- I have little faith the world will “answer the bell” sort of speak and end global warming.
I have similarly little faith that this will happen but a lot of hope that it will. Among the reasons is that it is both environmentally and economically wise to stop climate change as the cost to do so is tiny (some claim it is negative – or a gain rather than a cost) compared to the costs of the damages incurred from unchecked climate change. In other words, the idea that there is a tradeoff between the economy and the environment is a completely false one. So, having a lot of faith in the greed of humanity gives me more hope that we will act to slow and stop climate change.
The boreal forest is one of the world’s largest intact forests. Researchers noted the forest supplies timber, house biodiversity and helps slow climate change by catching and holding “a significant portion of the planets terrestrial carbon.”
More research is needed to understand potential changes by using combinations of experiments, observations and models. However, long-term experiments like the one conducted by the U. of M. are rare. Worldwide, only one other long-term study like this has been conducted in a spruce bog in northern Minnesota.
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