Trees, the lungs of the world, or are they?
We all know about photosynthesis. We all know that trees combine carbon dioxide and water with energy from sunlight to form complex carbohydrates and oxygen as a waste product. From our school days we remember that the catalyst is chlorophyll the green pigment in the leaves. We also remember that the carbohydrate is initially sugar that is passed around the tree in solution and used to form the various types of fibres and cells that ultimately become leaves, stalks, roots, wood and bark so that the tree grows.
Taking in carbon dioxide and giving back oxygen is exactly what we need to combat the effects of the key greenhouse gas, carbon dioxide which we are told is rising because of all the fossil fuels we are burning. Indeed trees are regarded by many as “the lungs of the world” crucial to the well being of the planet.
If only it were that simple. The first paragraph above is of course true but I can remember the school teaching and there was more to it than that. Photosynthesis is only half the story, it is the “up” half of the Carbon Cycle. The down half of the cycle is decomposition of which there are two kinds, aerobic and anaerobic e.g. with and without oxygen. Virtually all trees are subject to aerobic decomposition very few drop into bogs or sink into deep stagnant water to become subject to anaerobic decomposition. In other words they nearly all either rot where they drop or burn, with or without our help but always with complete access to atmospheric oxygen. A proportion, those in the “sustainable” commercial forests are harvested, milled into boards and used to make things but in the main its only a matter of time before these trees too either rot or burn. Of course along the way the larger proportion of this wood is wasted as sapwood, branches sawdust, shavings and off-cuts. Plus, don’t forget that as much wood exists in the form of roots under the ground as branches above ground and this is always left behind.
The quick way to decompose a tree is by burning it. Very rapidly all the carbon-based substances absorb oxygen and decompose to carbon dioxide and water leaving you right back where you started, with nothing e.g. no net gain in oxygen in the atmosphere and no net removal of carbon dioxide either. Decomposition by rotting is far slower but the net result is exactly the same. Even the amount of heat generated is the same its just that a compost heap will stay hot inside for months but as a bonfire it will be gone in less than an hour. The heat is the stored sunshine and as the carbon dioxide and water go back where they came from the heat is released too.
The proof of this is in the rain forests. They have been growing vast tonnages of wood for millions of years. If the capturing of carbon from the atmosphere had been permanent the soil in the rain forests would be jet-black with carbon and hundreds of feet thick. The reality is that the soil is only inches thick and very poor stuff, exhausted within a year or so of clearing it for normal agriculture. The rain forest environment is not just one of rapid growth it is balanced by equally rapid putrefaction.
If you want to make a difference with a tree you must cut it down the instant it reaches maturity and convert the wood into products that will be preserved for all time. Very little wood achieves this ideal.
Where then does our oxygen come from? The answer is in fact in the carbon cycle after all but in the down side, anaerobic decomposition. Any plant growth, taking place on a global scale but not subject to aerobic decomposition will yield a net gain to the atmosphere. The process we are looking for is in our oceans. Down in the deeps the available oxygen is rapidly depleted and not replenished so sinking carbohydrates (dead plants) decompose to hydrocarbons and really are jet-black and hundreds of feet deep. Later they compress down into fossil fuels for another generation to use.
As we burn vast tonnages of fossil fuels we need a means of accelerating the oceanic carbon cycle to compensate. The solution is to dump vast tonnages of fertilisers in to boost aquatic plant growth. By a complete fluke this is exactly what we have been doing for a long while now but we are currently regarding it as nitrate pollution, it is not, it is global repair. All the fertilisers we spread on our fields eventually wash off and pass out to sea. It must not stop!.
The carbon cycle holds true for all land based plant life not just trees, it all takes in carbon dioxide and gives back oxygen while it grows, then rots back to carbon dioxide, consuming all the oxygen it made in life, after it dies. In fact if you set aside all the emotive issues and just look at your landscape you will see that trees actually represent a fairly small percentage of the greenery. I think that globally the grasses will be dominant. It is easier to see the full cycle taking place with the grasses especially where animals eat it.
Time for the real science, here is the process of photosynthesis;
6CO2 + 12H2O + Light Energy > C6H12O6 + 6O2 + 6H2O
e.g. carbon dioxide plus water plus sunshine becomes carbohydrate plus oxygen plus less water
Then the process going back as in rotting , animals or burning, in order of speed;
C6H12O6 + 6O2 + 6H2O > 6CO2 + 12H2O + Heat
e.g. carbohydrate plus oxygen plus some water becomes carbon dioxide plus more water plus heat. The equations are exactly the same both ways provided only that we express the sunlight and the heat as energy equivalent.
The above is why the closed environment experiments (the Biosphere’s) failed, they had people and animals in them and aerated compost heaps instead of anaerobic decomposing tanks. They needed bulk plant matter grown solely to be rotted away from oxygen and from the equations above they needed as much of it as they grew for food. Instead they just grew food and recycled everything “organically” and in a matter of a few months came close to suffocation. As what they started out with oxidised
I frankly do not understand how supposedly fully qualified scientists can make such a fundamental mistake but if you go on the web and search on “biosphere” you will find a huge amount of published material. You will find that the projects simulated everything in real life but on a small scale oceans being represented by ponds of salt water supporting sea flora plus they have fresh water ponds with fresh water plants and so on. They do not have enough depth however to achieve oxygen depletion (this requires thousands of feet) so all organic decomposition in the whole closed environment was aerobic, producing no net new oxygen and absorbing no net carbon dioxide. As soon as people and animals moved in there was a day by day deficit in oxygen and a rise in carbon dioxide until it became dangerous and fresh air had to be let in.
The fallacy is very widespread, the oil companies have got round the global anti-greenhouse agreements by buying up large tracts of rain forests balancing calculated “carbon dioxide/oxygen” recycling against hydrocarbon fuel sales. I don’t actually believe that they really have made a mistake. I believe that they are fully aware that it is a fallacy but are cynically exploiting this very well entrenched myth