Tropical Forest will be Carbon source than Sink

We have heard a lot about terms such as Carbon sink and carbon source.

Photo by Pawel Janiak on Unsplash

Source is a place from where carbon is generated. Which is not that difficult to guess, like factories, fossil fuels, vehicle emissions etc.

Whereas sink is place which stores the carbon more than it releases.

So a forest is a carbon sink or a source depends upon the balance between photosynthesis and respiration. During photosynthesis a tree takes up carbon which means it is taking carbon from atmosphere. For which we use the term carbon sequestration. It builds its part by this carbon.

The carbon cycle (Illustration: Lisa Larsson)

During lifetime of a tree it gives out carbon also in form of respiration. Which is half of the carbon stored in it by photosynthesis. Even forest soil has sequestered a lot of carbon.

So when this carbon sequestration is more than carbon release from a forest it is called as a sink. If opposite is true it is a source. Now forest can act as a carbon source also when it has a lot of dying trees and incidents like large forest fire. A forest is a carbon source in short interval or a sink also depends upon whether it is intact & doing its job fine or it is being degraded or deforested speedily. Which means there are leakages.

When a tree dies the micro bacteria do its job and some of the carbon the tree stored in it throughout its life is released back to the atmosphere.

Decomposition of a dead tree mass is half in four years and 85% in ten years, says the research. Not all carbon is lost in this process. Good amount is stored in soil.

Big patch of forest are a good carbon sink for example Amazon. In 1990s the intact tropical forests removed about 17% of anthropogenic C02 emissions. Which is huge given the amount of CO2 emissions happening all over the world.

Now a study showcase that the carbon sink of these tropical forests is reducing its strength as a lot of trees are dying. The carbon sequestration capacity of a tree is inverted U shape. It peaks and then the strength keep reducing. So even if people cut trees before maturity the process of carbon capturing of a large patch reduces as comparison to situation when we leave them to mature. Say unplanned or unchecked deforestation.

The study summaries that the sink strength of intact tropical forests has declined by 33% by 1990s and 2010s. Which is very alarming. This study talks about carbon sinks of intact tropical forests in Africa and Amazon. Given that these tropical forests are very important carbon sinks.

Fig. | Modelled past and future carbon dynamics of structurally intact old-growthtropical forests in Africa and Amazonia. a–f, Predictions of net aboveground live biomass carbon (a, d), carbon gains (b, e), and carbon losses (c, f), for African (left panels) and Amazonian (right panels) plot inventory networks, based on CO2-change, MAT, MAT-change, drought (MCWD), plot wood density, and plot CRT, using observations in Africa until 31 December 2014 and Amazonia until mid-2011, and extrapolations of prior trends to 31 December 2039. Model predictions are in blue (Africa) and brown (Amazon), with solid lines spanning the window when ≥75% of plots were monitored to show model consistency with the observed trends, and shading showing upper and lower confidence intervals accounting for uncertainties in the model (both fixed and random effects) and uncertainties in the predictor variables. Light-grey lines and grey shading are the mean and 95% CI of the observations from the African and Amazonian plot networks. (Source)

And soon it will become a carbon source according to this study which is very alarming. If this is coupled with rapid deforestation and forest fires it is the most dangerous thing as we are already dependent on these forests for carbon sequestration.

Which means all our global warming equations need to be looked again as we will see not so good things happening earlier than predicted. This also means that we cant just use more environment degrading things and wait for these forests to do their job. This also means that if we don’t stop deforestation and forest fire ( a burning forest is huge carbon source ) now then it will be too late. Rather we need to conserve these tropical forests for biodiversity and ecological services they provide.