How much do trees vary in the way they suck carbon dioxide from the air and use it to make roots, trunks, branches and leaves? The answer to that question is an important one because it has a huge impact on our ability to predict how destroying or creating forests influences climate change. And the correct answer is a surprising one, according to two related studies published in the Proceedings of the National Academy of Sciences this week by University of Minnesota forest ecologist Peter Reich and colleagues in Minnesota, Arizona, Australia, China, Poland and Germany.
Conventional models used to assess the impact of forests on greenhouse gas concentrations in the atmosphere assume that the way trees use carbon to build roots, leaves and trunks is fairly constant across a range of conditions — that is, that trees everywhere devote the same fraction of new growth to each component and that components have the same durability everywhere. However, analyzing massive amounts of data gathered from around the globe, Reich and colleagues documented predictable differences in key properties of forests across north-south climate gradients.
“These findings both advance our understanding of how trees vary and provide useful tools for making earth system models more accurate,” said Reich, a Regents professor and distinguished McKnight University professor in the College of Food, Agricultural and Natural Resource Sciences and resident fellow of the Institute on the Environment. “[Most of all, they dramatically improve our ability to accurately assess the impact of forests on climate change and vice versa.]”
In one paper, the scientists addressed the question of whether trees invest more heavily in building roots to enhance uptake of water and nutrients in cold climates, where these resources are scarce. Using data from more than 6,000 forests in 61 countries, the researchers discovered that cold-climate forests tend to build more roots and less leaves than those found in warmer climates. This information will improve scientists’ ability to estimate how much carbon trees store worldwide.
The second study looked at how the amount of time cold-climate evergreens such as spruce, fir and pine hang onto their needles varies with climate. Until now, research looking at the flow of carbon through ecosystems generally assumed that evergreens like spruce and pine keep their needles for an average of two years pretty much everywhere. These new findings, gathered from more than 125 sites in North America and Europe, paint a far different picture. The researchers found that the needles of evergreen trees such as spruce and pine in the cold, far north of Canada and Scandinavia last longer but have a lower capacity for capturing carbon than do needles of trees in warmer (relatively speaking) climates such as Minnesota or Germany. These north-south geographic patterns are similar enough among pines and spruces and Europe and North America to enable their incorporation into global vegetation and earth system models, resulting in more accurate projections of forest productivity, carbon flow and how forest are likely to change in the future.
The research involved multiple partners, including a large IonE-sponsored initiative, the Plant Data Synthesis project, which seeks to bring together massive amounts of data from around the world in search of big-picture patterns related to how trees and forests function.
“By improving our understanding of how forests vary from tropics to temperate zone to the polar edges of boreal forest, we hope to provide fundamental advances to basic science and new tools for better modeling forest growth and climate regulation today and into the future,” Reich said.
The University of Minnesota’s Institute on the Environment seeks lasting solutions to Earth’s biggest challenges through research, partnerships and leadership development. For more information, visit environment.umn.edu.
Photo by Jim Brekke (Creative Commons / Flickr)