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Context: A new study has found that tropical forests, which have been logged (cut down) or degraded, remain a source of carbon emission for at least a decade.

Details:

• According to a 2014 NASA-led study, tropical forests remove up to 30 per cent of human carbon dioxide emissions from the atmosphere and make for an important carbon sink — an area which absorbs more carbon than releases it.
• The findings are contrary to a previous assumption – that recovering tropical forests absorb more carbon than they emit into the atmosphere because they witness rapid re-growth of trees.
• The latest study, ‘Tropical forests post-logging are a persistent net carbon source to the atmosphere’, is published in Proceedings of the National Academy of Sciences.

What is carbon sequestration and how do forests play a role in it?

• Carbon sequestration is a crucial part of the global carbon cycle, as it is the process of capturing and storing atmospheric carbon dioxide.
• One of the ways this happens is when forests and other land vegetation absorb carbon dioxide during photosynthesis.

What makes this study’s findings different?

• Many of the previous studies on recovering tropical forests estimated the amount of carbon being absorbed by them by only focusing on the regrowing of the trees.
• This means they are only measuring the sink function of the forest.
• If you imagine your bank account – it would be like only looking at your incomings, not your outgoings
• Unlike their predecessors, the team also looked into how much carbon was released from the ground, meaning from soil and deadwood, to calculate the overall carbon budget of the logged and unlogged forests.

What are the findings of the study?

• The study observed that while intact or unlogged forests are generally carbon-neutral (they release and absorb roughly the same amount of carbon), logged or degraded forests remain a “net source of carbon” for up to a decade.
• This happens because such forests tend to have damaged soil and large deadwood stocks, originating from abandoned logs and collateral damage during logging. Soil and deadwood naturally release carbon when they decay.
• According to a 2011 study, tropical forests across the world absorbed 15 per cent of all human-generated CO2 emissions between 1990 and 2007. Experts suggest that if the logging of these forests continues, it would be impossible to curtail the rising global temperatures.

What is a tropical forest?

• Tropical forests are closed canopy forests growing within 28 degrees north or south of the equator.
• They are very wet places, receiving more than 200 cm rainfall per year, either seasonally or throughout the year. Temperatures are uniformly high - between 20°C and 35°C.
• Such forests are found in Asia, Australia, Africa, South America, Central America, Mexico and on many of the Pacific Islands. 
• Rainforest trees are quite different from trees of temperate forests.
• In the rainforest, trees grow to gigantic size, supported by strong, strut-like buttresses at the base of the trunk that help to stabilize them in shallow forest soils. Huge creepers twine themselves around the trunks of trees.
• A mature lowland tropical forest consists of several layers. The top layer of vegetation consists of scattered tall trees which tower above a closed canopy layer formed by the crowns of other trees.
• The canopy is the most exciting part of the rainforest; it is here that most of the flowering and fruiting of the trees takes place, attracting a variety of spectacular creatures.
• Below the canopy is a third layer, formed by smaller trees whose crowns do not meet. Below that is a layer that's composed of woody and herbaceous shrubs. Finally, there is the ground layer, which receives very little sunlight.

https://indianexpress.com/article/explained/explained-climate/new-study-logged-tropical-forests-emit-carbon-8379480/

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