How effective has afforestation been worldwide

Saving the world with trees : Researchers doubt study on afforestation against climate change

There is nothing more effective in combating climate change than afforestation - this study result, published in the summer, has met with criticism from other researchers. The potential of tree planting to contain climate change was dramatically overestimated in the study, according to the Leuphana University of L√ľneburg on Tuesday. The Leuphana researcher Vicky Temperton was co-author of a current statement in the journal "Science" on the analysis presented at the beginning of July.

Planting trees in the wrong places could even destroy ecosystems, increase the intensity of forest fires and exacerbate global warming, explain researchers working with Temperton and Joseph Veldman from Texas A&M University in the USA. Researchers from numerous other universities and institutes such as the LMU Munich, the University of Bonn and the Max Planck Institute for Meteorology in Hamburg are also critical of the study in "Science".

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Potential five times overestimated

Researchers at the Swiss Federal Institute of Technology (ETH) in Zurich wrote in the summer in "Science" that the earth could tolerate a third more forests without affecting cities or agricultural areas. Planting trees has the potential to absorb two thirds of the climate-damaging CO2 emissions previously caused by humans.

The new forests could therefore store 205 billion tons of carbon when they grew - about two-thirds of the 300 billion tons of carbon that has been released into the atmosphere by humans since the Industrial Revolution.

The value of 205 billion tons of carbon is set far too high, according to the critical contribution made by Veldman's researchers. Serious deficiencies would have led to a five-fold overestimation of the potential of newly planted trees for mitigating climate change.

The study assumes, for example, that soils in ecosystems without trees contain no carbon - in many habitats such as savannas and peat bogs, however, more carbon is bound in the soil than in the vegetation above ground. "Ecological remediation could contribute much more to natural climate solutions if we not only focus on forests, but also take care of grasslands, savannas, bushland and peat bogs," says Temperton.

Another criticism is that the Swiss scientists overestimate the potential of afforestation because pasture areas will continue to spread around the world over the next few decades and will then not be available for tree planting. However, the Swiss researchers rated the pastures as potential areas for afforestation.

The criticized stick to their assessment

The Zurich scientists around Jean-Francois Bastin also respond to the criticism in "Science". For example, they write that it is entirely possible that they overestimate or underestimate the potential of afforestation with their model in some places. Your analysis should be understood under current circumstances. If there is more pasture area, the area that is available is of course also reduced. At the same time, however, they refer to studies according to which it is quite possible to plant a large number of trees on pastureland without reducing the yield.

Overall, even after the criticism, the researchers stick to their assessment that they even underestimated the potential of tree planting in their study. This is mainly due to the fact that they have assumed zero reforestation potential for arable land and cities. You write, "Indeed, both farmlands and cities offer great opportunities to increase the current tree population and play an important role in mitigating climate change." (fsch, dpa)

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