A global analysis reveals for the first time that across almost all tree species, fast-growing trees have shorter lifespans—the greater is the tree growth more significant will be carbon storage in forests in the long term. The findings are published today in Nature Communications (Brienen et al. 2020).
Currently, forests absorb large amounts of carbon dioxide (CO2) from the atmosphere. The phenomenon may be due to higher temperatures and abundant CO2 stimulating growth in trees, allowing them to absorb more CO2 as they grow.
Most earth system models predict that this growth stimulation will continue to cause a net carbon uptake of forests this century. But, the study, led by the University of Leeds, casts doubts on these predictions.
The study confirms that accelerated growth results in shorter tree lifespans and that growth-lifespan trade-off are indeed near-universal, occurring across almost all tree species and climates. The work suggests that increases in forest carbon stocks may be short-lived.
In a press release, the lead author of the study, Dr. Roel Brienen from the School of Geography at Leeds, said: “While it has been known for a long time that fast-growing trees live shorter, so far this was only shown for a few species and at a few sites.
“Our modeling results suggest there is likely to be a time lag before we see the worst of the potential loss of carbon stocks from increases in tree mortality. They estimate that global increases in tree death don’t kick in until after sites show accelerated growth.
The trade-off may be due to environmental variables affecting tree growth and lifespan, as co-author Dr. Alfredo Di Filippo reported that the lifespan of beech trees in the Northern Hemisphere decreases by roughly 30 years for each degree of warming.
The current analysis confirms that, across biomes, reductions in lifespan are not due directly to temperature per se, but are faster growth at warmer temperatures.
Their findings suggest that a prominent cause of a growth lifespan trade-off’s widespread occurrence is that chances of dying increase dramatically as trees reach their maximum potential tree size.
Other factors such as—trees that grow fast may invest less in defenses against diseases or insect attacks and may make the wood of lower density or water transport systems more vulnerable to drought—may also play roles in the process.
In the press release, study co-author Dr. Steve Voelker, from the Department of Environmental and Forest Biology, Syracuse, New York, said: “Our society has benefitted in recent decades from the ability of forests to increasingly store carbon and reduce the rate at which CO2 has accumulated in our atmosphere. However, carbon uptake rates of forests are likely to be on the wane as slow-growing and persistent trees are supplanted by fast-growing but vulnerable trees.”
Brienen, R. J. W., L. Caldwell, et al. (2020). “Forest carbon sink neutralized by pervasive growth-lifespan trade-offs.” Nat Commun 11(1): 4241.
Harrison, A. (2020). “Trees living fast die young.” 2020.
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