May 15, 2019
University of Cambridge
Accelerated tree growth caused
by a warming climate does not necessarily translate into enhanced carbon
storage, an international study suggests.
Accelerated tree growth caused
by a warming climate does not necessarily translate into enhanced carbon
storage, an international study suggests.
The team, led by the
University of Cambridge, found that as temperatures increase, trees grow
faster, but they also tend to die younger. When these fast-growing trees die,
the carbon they store is returned to the carbon cycle.
The results, reported in the journal Nature
Communications, have implications for global carbon cycle dynamics. As the
Earth's climate continues to warm, tree growth will continue to accelerate, but
the length of time that trees store carbon, the so-called carbon residence
time, will diminish.
During photosynthesis, trees
and other plants absorb carbon dioxide from the atmosphere and use it to build
new cells. Long-lived trees, such as pines from high elevations and other
conifers found across the high-northern latitude boreal forests, can store
carbon for many centuries.
"As the planet warms, it
causes plants to grow faster, so the thinking is that planting more trees will
lead to more carbon getting removed from the atmosphere," said Professor
Ulf Büntgen from Cambridge's Department of Geography, the study's lead author.
"But that's only half of the story. The other half is one that hasn't been
considered: that these fast-growing trees are holding carbon for shorter
periods of time."
Büntgen uses the information
contained in tree rings to study past climate conditions. Tree rings are as
distinctive as fingerprints: the width, density and anatomy of each annual ring
contains information about what the climate was like during that particular
year. By taking core samples from living trees and disc samples of dead trees,
researchers are able to reconstruct how the Earth's climate system behaved in
the past and understand how ecosystems were, and are, responding to temperature
variation.
For the current study, Büntgen
and his collaborators from Germany, Spain, Switzerland and Russia, sampled more
than 1100 living and dead mountain pines from the Spanish Pyrenees and 660
Siberian larch samples from the Russian Altai: both high-elevation forest sites
that have been undisturbed for thousands of years. Using these samples, the
researchers were able to reconstruct the total lifespan and juvenile growth
rates of trees that were growing during both industrial and pre-industrial
climate conditions.
The researchers found that
harsh, cold conditions cause tree growth to slow, but they also make trees
stronger, so that they can live to a great age. Conversely, trees growing
faster during their first 25 years die much sooner than their slow-growing
relatives. This negative relationship remained statistically significant for
samples from both living and dead trees in both regions.
The idea of a carbon residence
time was first hypothesised by co-author Christian Körner, Emeritus Professor
at the University of Basel, but this is the first time that it has been confirmed
by data.
The relationship between
growth rate and lifespan is analogous to the relationship between heart rate
and lifespan seen in the animal kingdom: animals with quicker heart rates tend
to grow faster but have shorter lives on average.
"We wanted to test the
'live fast, die young' hypothesis, and we've found that for trees in cold
climates, it appears to be true," said Büntgen. "We're challenging
some long-held assumptions in this area, which have implications for
large-scale carbon cycle dynamics."
Story Source:
Materials provided by University of Cambridge. The
original story is licensed under a Creative Commons License. Note:
Content may be edited for style and length.
Journal Reference:
Ulf Büntgen, Paul J. Krusic,
Alma Piermattei, David A. Coomes, Jan Esper, Vladimir S. Myglan, Alexander V.
Kirdyanov, J. Julio Camarero, Alan Crivellaro, Christian Körner. Limited
capacity of tree growth to mitigate the global greenhouse effect under
predicted warming. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-10174-4
