Trees with faster growth rates are dying younger in several countries and species, reducing their overall carbon storage capacity, according to a new study.
The researchers analyzed tree ring data from more than 200,000 records from 110 species in Europe, Asia and America.
They found that faster tree growth, as indicated by tree rings, caused earlier mortality and the release of the carbon into the atmosphere.
Many scientists believe that planting more trees will offset the amount of carbon dioxide (CO2) emissions caused by human activity.
However, a shorter lifespan for trees makes them grow faster and have less time to absorb the CO2 than expected, the new study says.
The new study also challenges predictions that greater tree growth means greater carbon storage in forests in the long term.
Nothofagus pumilio (southern beech) forests around Lake Argentino, in the Andes of southern Patagonia, Argentina, show clusters of dead trees. The global analysis shows that fast growing trees have a shorter lifespan for almost all tree species
An increase in CO2 in the atmosphere – a key component in photosynthesis – can trigger growth spurts for tree species, but too much can have negative consequences
"While it has long been known that fast-growing trees live shorter lives, this has so far only been shown for a few species and in some locations," said study author Dr. Roel Brienen from the University of Leeds.
& # 39; We started a global analysis and were surprised that these tradeoffs are incredibly common.
"It was found in almost every species we looked at, including tropical trees."
Forests currently absorb large amounts of carbon dioxide (CO2) from the atmosphere. Stimulation of tree growth.
A relationship between faster tree growth rates and shorter tree lifetimes has already been shown in some trees, especially in cold-adapted conifers.
However, whether this applies to all species and climates is debatable.
Tree rings from Hymenaea courbaril (Leguminosae) from the Neotropic. 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).
Dr. Brienen and colleagues analyzed a large data set of tree ring data that represent tree species on every continent except Africa and Antarctica.
Tress can be aged by measuring its girth – especially the rings that develop over time and increase that girth.
They report that faster growth is associated with a shortened lifespan of trees both within and within tree species.
The compromise between fast growth rates and slow lifespans has the potential to slow down or even reverse the global carbon sink in forests in the future.
Compromises between growth and lifespan are also almost universal and occur in almost all tree species and climates.
This suggests that the increase in forest carbon stocks – carbon that is captured from the atmosphere and stored in the forest ecosystem in living biomass, soil and dead wood – can only be short-lived.
A reduced future carbon sink in the forest, which will increase CO2 in the atmosphere in the near future, further increases the urgency to curb greenhouse gas emissions.
"Our modeling results suggest that there will likely be a time lag before we see the worst potential loss of carbon stocks from the increase in tree mortality," said Dr. Brienen.
Previous research has shown that tree mortality rates in the Amazon forest increase over the long term and lag behind the increase in tree growth (Figure).
"They estimate that the global increase in tree death will only set in after the sites show accelerated growth."
"This is in line with observations of increasing tree death trends around the world."
Previous research at the University of Leeds found that long-term increases in tree mortality rates lag behind increases in tree growth in the Amazon forest.
In other words, trees die before they are big enough to store significant amounts of carbon from the atmosphere.
And the likelihood that trees will die increases dramatically when they reach their maximum potential tree size.
The team acknowledges that other factors may still play a role in trees that die earlier than usual.
For example, fast-growing trees can invest less in warding off disease or insect infestation.
As a result, they can develop lumber with lower density or with water transport systems that are more prone to drought.
"Our results, which are very similar to the history of the turtle and the hare, show that the fastest growing trees have characteristics that make them vulnerable while slow growing trees have characteristics that enable them to survive," the said Study author Dr. Steve Voelker from the Department of Environmental and Forest Biology, New York.
“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 persistent trees are replaced by fast-growing but endangered trees."
David Lee, a professor of atmospheric science at Manchester Metropolitan University, who was not involved in the study, said the idea that tree planting could offset fossil fuel emissions "doesn't stand up to scientific scrutiny."
"Detailed and careful studies like these are critical to determining the viability of future carbon sinks or negative emissions technologies to keep temperatures at 1.5 degrees Celsius (2.7 degrees Fahrenheit) through the end of the century."
According to a declaration by the United Nations in December, we are nowhere near on track to achieve this goal, as set out in the 2015 Paris Agreement.
The study was published in Nature Communications.
WHAT IS THE PARIS AGREEMENT?
The Paris Agreement, first signed in 2015, is an international agreement to control and limit climate change.
She hopes to keep the global mean temperature rise below 2 ° C (3.6 ° F) and efforts to limit the temperature rise to 1.5 ° C (2.7 ° F).
It seems that the more ambitious goal of keeping global warming to 1.5 ° C (2.7 ° F) may be more important than ever. This is what previous research suggests that 25 percent of the world could see a significant increase in drier conditions.
In June 2017, President Trump announced his intention to have the US, the world's second largest greenhouse gas producer, withdraw from the deal.
The Paris Agreement on Climate Change has four main objectives in terms of reducing emissions:
1) Long-term goal to keep the increase in global average temperature well below 2 ° C above the pre-industrial level
2) The aim is to limit the rise to 1.5 ° C as this would significantly reduce the risks and impacts of climate change
3) Governments agreed that global emissions must peak as soon as possible and recognized that it will take longer for developing countries
4) then make rapid reductions based on the best scientific evidence available
Source: European Commission
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