Are forests growing?

Article by Isabel Key and Mina Frost.

The world has around 3 trillion trees [1]. Humans are thought to cut down around 15 billion each year [1]. Some forest is also killed by fire, drought, insects, and disease [16,19]. Tree loss is concentrated in tropical areas, with Brazil having the highest rates of forest loss [16]. This is causing tropical forests to now release more CO2 into the air than they take in [18].

However, the total area of forest is thought to be increasing globally [16]! This has mostly been in Russia, China, and the USA [16]. This is due to people abandoning farms and moving into cities, as well as warming temperatures allowing forests to move higher up mountains, and to spread closer to the poles [16].

We also plant trees, such as in China, India, and Ethiopia [11,12,13,14]. However, these newly planted forests are often ‘monocultures’ (that is, they have only one type of tree) making them vulnerable to dying from fire, drought, storms, and disease [3,17].

Are trees themselves growing bigger? Some, yes! This is because higher temperatures mean that trees can grow for a larger part of the year [2], and because there is more CO2 in the air for trees to use to make wood, sometimes making them grow faster [6,15]. Some trees in Europe (spruce and beech) are growing up to 77% faster than in 1870 [7]!

Does this mean forests take in more carbon, slowing global warming? Nope, unfortunately not [2]. The amount of carbon in some tree wood has decreased by ~50% – they are growing faster but not taking up more CO2 [2]. Plus, the wood of some trees is becoming weaker, due to heat and air pollution damaging the wood, making them more likely to break in storms [2].

Conclusion: The total area of forest is increasing, but the ‘quality’ of forests is decreasing. At the moment forests slow global warming by taking up CO2, but global warming may make death from drought and fire so common, that forests may actually add to global warming in the future [9,10,20].

References

[1] https://www.nature.com/news/global-count-reaches-3-trillion-trees-1.18287

[2] https://www.sciencemag.org/news/2018/08/climate-change-making-trees-bigger-weaker

[3] https://www.nature.com/articles/s41558-019-0405-0

[4] https://www.theguardian.com/environment/ng-interactive/2018/jun/27/one-football-pitch-of-forest-lost-every-second-in-2017-data-reveals

[5] https://www.globalforestwatch.org/

[6] https://www.ncbi.nlm.nih.gov/pubmed/30588740

[7] https://www.nature.com/articles/ncomms5967

[8] https://royalsocietypublishing.org/doi/abs/10.1098/rstb.2003.1429?casa_token=WiWl4pboFGUAAAAA:AhtfLeKfBGcA7WeplV0tB9DkxSKeyo8w6ukTLFK5WSuekNtpMdPwdB4c-UgyaIq5AWlA_3RFxHgMsgo

[9] https://www.sciencedaily.com/releases/2019/08/190821135257.htm

[10] https://www.cnbc.com/2017/09/29/tropical-forests-have-become-a-net-carbon-source-study.html

[11] https://www.theguardian.com/commentisfree/2018/feb/13/worlds-lost-forests-returning-trees

[12] https://www.bbc.co.uk/news/world-africa-49266983

[13] https://www.independent.co.uk/news/world/asia/india-plant-66-million-trees-12-hours-environment-campaign-madhya-pradesh-global-warming-climate-a7820416.html

[14] https://www.carbonbrief.org/one-third-worlds-new-vegetation-in-china-and-india-satellite-data-shows

[15] https://www.scientificamerican.com/article/ask-the-experts-does-rising-co2-benefit-plants1/

[16] https://psmag.com/environment/the-planet-now-has-more-trees-than-it-did-35-years-ago

[17] https://www.nationalgeographic.com/environment/2019/04/how-to-regrow-forest-right-way-minimize-fire-water-use/

[18] https://science.sciencemag.org/content/358/6360/230

[19] http://www.fao.org/3/i0670e10.htm

[20] https://www.annualreviews.org/doi/abs/10.1146/annurev-earth-082517-010235

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