Cross-sectional view of Austrocedrus chilensis wood in the Andes of Northern Patagonia, Argentina.
This species is abundant in the ecotone of the Xerian forest-steppe, where periodic massive mortality events occur
was documented in connection with extreme droughts in Patagonia in the 20th century. Photo credit: Ricardo Villalba, Instituto Argentino de Nivología, Glaciología and Ciencias Ambientales (IANIGLA-
CONICET)
A global analysis shows for the first time that fast-growing trees have a shorter lifespan in almost all tree species. This international study also challenges predictions that greater tree growth means greater carbon storage in forests in the long term.
Forests currently absorb large amounts of carbon dioxide (CO2) from the atmosphere. It is believed that this is due to higher temperatures and abundant CO2, which stimulates the growth of trees and allows them to absorb more CO2 as they grow.
Most Earth system models predict that this stimulation of growth will continue to result in net carbon uptake by forests this century. But the study, led by the University of Leeds and published today in Communication with naturecasts doubt on these predictions.
Nothofagus pumilio (southern beech) forests around Lake Argentino in the Andes in southern Patagonia, Argentina, show clusters of dead trees related to the severe drought in the Australian summer of 2011-2012. Incremental cores from dead trees give these individuals an age between 150 and 300 years. Photo credit: Ricardo Villalba, Instituto Argentino de Nivología, Glaciology and Ciencias Ambientales (IANIGLA-CONICET)
The international study is the largest to date that deals with the relationship between tree growth and tree lifespan. The researchers examined more than 200,000 tree ring records from 82 tree species in locations around the world.
Tree seedling that starts life in the rainforest, Peru. Photo credit: Roel Brienen, University of Leeds
It confirms that accelerated growth results in shorter tree lifespan and that the trade-offs between growth and lifespan are indeed nearly universal and occur in almost all tree species and climates. This suggests that an increase in forest carbon stocks can only be short-lived.
The study’s lead author, Dr. Roel Brienen of the School of Geography in Leeds said: “Although it has long been known that fast-growing trees live shorter, this has only been shown for a few species and on a few websites.
“We started a global analysis and were surprised that these compromises are incredibly common. It was found in almost every species we looked at, including tropical trees.
“Our modeling results suggest that there will likely be a time lag before we see the worst potential loss of carbon stocks due to an increase in tree mortality. They estimate that the global increase in tree death will only set in after the locations show accelerated growth.
“This is in line with observations of increasing tree death trends around the world. For example, previous Leeds research has shown that tree mortality rates lag behind tree growth rates in the Amazon forest over the long term. ”
Tree rings from Hymenaea courbaril (Leguminosae) from the Neotropics. These tree rings formed during the rainy season are bounded by visually distinct bands known as edge parenchyma bands (boundaries indicated by the white arrows). Photo credit: Giuliano M. Locosselli and Milena Godoy-Veiga
Co-author Prof. Manuel Gloor, also from the School of Geography, said: “Earth system models often fail to take account of these negative feedbacks or fail to take them into account, and model projections of the persistence of the global carbon sink in forests are therefore likely to be imprecise and overly optimistic. Our results suggest that a greatly reduced future carbon sink in the forest will further increase the urgency to curb greenhouse gas emissions. ”
Brazil nut tree (Bertholletia excelsa) in the rainforest of Bolivia, which can reach an age of over 450 years
Year old. Photo credit: Roel Brienen, University of Leeds
The tradeoff may be due to environmental variables that affect the growth and lifespan of trees. For example, co-author Dr. Alfredo Di Filippo from the University of Tuscia, Italy, previously stated that the lifespan of beeches in the northern hemisphere decreases by around 30 years with each degree of warming.
The current analysis confirms that the shortening of lifespan across biomes is not directly due to temperature itself, but to faster growth at warmer temperatures.
Their results suggest that a major cause of the widespread occurrence of the trade-off between growth lifetimes is that the likelihood of death increases dramatically as trees reach their maximum potential tree size.
However, other factors can also play a role. For example, trees that grow quickly can invest less in warding off disease or insect infestation and make wood with lower density or water transport systems more prone to drought.
The study co-author, Dr. Steve Voelker, of the Department of Environmental and Forest Biology, Syracuse, New York, said, “Our results, which are very similar to the history of the turtle and hare, show that there are features within the fastest growing trees that make them vulnerable while slow growing trees have properties that allow them to exist.
Balsam fir (Abies Balsamea) growth rings from Quebec, Canada, from four trees of different ages.
The wider the growth rings, the faster the tree will reach its maximum potential size. Fast growing trees
therefore have a shorter life expectancy. Credit: Quebec Department of Forests, Wildlife and Parks.
“Our society has benefited over the past decades from the ability of forests to increasingly store carbon and to slow the rate at which CO2 has accumulated in our atmosphere. However, forest carbon uptake rates are likely to decrease as slow-growing and perennial trees are replaced by fast-growing but vulnerable trees. ”
Reference: “The carbon sink of the paper Forest neutralized by the omnipresent compromises between growth and service life”, September 8, 2020, Communication with nature.
DOI: 10.1038 / s41467-020-17966-z
