Tree study has little practical value
HOUGHTON – A recent U.S. Geological Survey-sponsored study garnered widespread attention with its conclusion that the world’s oldest and largest trees grow faster than others of their species, rebutting long-held beliefs that growth slows and eventually stops when trees reach a certain size – years before they actually die.
But according to Michigan Technological University forestry professor Dr. Robert Froese, the results aren’t that remarkable when the study’s methodology is taken into account.
“The devil is in the details. They looked only at the very largest trees in very productive places,” he said. “They have to be successful to become the largest trees, so to say that the largest are successful isn’t that surprising.”
The study was published in the journal Nature by lead author Nate Stephenson, in collaboration with 37 other researchers from around the world. They used data on over 670,000 trees from 403 species gathered on six continents.
Stephenson concluded that in terms of mass – not necessarily height – growth actually accelerates as trees grew older. More significantly, “it also means that big, old trees are better at absorbing carbon from the atmosphere than has been commonly assumed,” Stephenson stated in a USGS press release.
Scientists agree that plants’ absorption, or sequestering, of carbon reduces carbon dioxide in the atmosphere, which would otherwise contribute to global warming.
Froese found the carbon findings interesting, and possibly relevant to academic understanding of the dynamics of carbon cycling, but not likely to be useful to forest management or practical efforts to fight global warming.
“I don’t see the implications. The result is really just confirming a pattern that is relevant only in a very narrow case,” he said. “It doesn’t really change anything we would do on the ground.”
In fairness, however, “the authors were not intending that the study would change our understanding of forestry in a dramatic way, but that it would contribute to our understanding of the larger picture.”
Another limitation of the study, Froese said, is that it excludes measurements from trees that have died, even if their growth had been tracked previously.
“They looked only at live trees,” he said, “so it’s not surprising that the trees that survive may be more likely to grow fast than trees that die sooner.”
Froese said he didn’t believe any Tech researchers were involved in gathering or analyzing data for the study, but species analyzed in the study included balsam fir, sugar maple, yellow birch and paper birch, all of which are common in the Copper Country.
But published data didn’t show where individual species were analyzed, or the climates, soils and ecosystems that may have influenced their growth.
According to the USGS release, all sampling was done in tropical, subtropical and temperate regions.
Technically, Michigan lies in a temperate latitude of the globe, the area south of the polar region and north of the tropics. But its actual climate is significantly colder than what would normally be considered temperate, due to its mid-continental location.
According to technical comments circulated by Paul C. Van Deusen, Craig Loehle and T. Bently Wigley of the National Council for Air and Stream Improvement, Inc., climactic and ecosystem considerations are crucial.
“It is, in fact, well-known that maximum tree height is limited by water supply and, if a tree cannot continue growing vertically, its growth will begin to slow,” the comments stated.
While the Stephenson study’s findings are open to debate and have limited implications, Froese said they nevertheless contribute to an understanding of the world we live in.
“It reveals that how you sample, and which parts of system you’re going to examine, affect the immediate impact,” he said. Also, it shows “how important it is that we integrate across all of the areas of knowledge we have for forest systems, to create sustainable results for forestry.”