Not all logging looks like this...

I'm working a project called Forest Degradation Experiment (FODEX). But what is 'degradation' exactly?

In short, degradation is damage short of destruction. But for an exact definition, you need to ask two things.

For a start, what is it you value in a tropical forest? Is the species richness? The amount of carbon stored in the trees? The ecosystem services it provides? Only once you assign value to something in the forest can you class it as damaged or degraded.

And secondly, where do you draw the line between the natural disturbances that are part of the forest life-cycle, and those disruptive, undesirable forms of change that you are going to class as degradation?

For our experiment, we're focusing on selective logging and calling that degradation. To understand why timber extraction in the tropics is degradation, it is important to realise that it doesn't always look anything like the large scale clear felling that we are used to seeing in the media.

In a hectare of tropical forest there could be hundreds of tree species. However, timber industries are typically only interested in a few 'big name' species who's wood is well known to be of good quality (think mahogany, teak...). On top of that, most of the trees in that hectare will be dwarfed by one or two giants that contain most of the wood. So there are tends to be a small handful of extremely valuable trees, but it simply isn't worth chopping the rest of the plot down. Those valuable trees will be cut down individually and extracted along their own little path (or skid trail) through the forest.

But why does this count as degradation? Surely the forest will simply grow back?

It is true that trees naturally die and fall down in the forest, and that saplings of 'pioneer' tree species then quickly grow up to take their place. However, logging activities tend to involve a lot of collateral damage. On average, for each log, around 5-10 trees die because they are brought down with it, severely damaged, or cleared to make access roads. The gap left behind is much larger than the average canopy gap from a natural death, and the heavy machinery involved can damage the soils. This means it can take the forest much longer to recover.

It takes decades for a logged area to regain the biomass it previously had, and centuries for species diversity to return to its previous levels. So logging of this kind can be done sustainably, but only at very low intensities. The other problem is that logging makes new areas of forest accessible to people, and very often this leads to clear-felling, burning and total land-use change.

Whilst we know that this kind of degradation happens, and it happens a lot (it's estimated selective logging supplies around 15% of world timber), we really can't say for sure how much it is being done, because unlike clear-felling, this degradation is pretty tricky to spot from space. That's the gap that we are trying to help fill with the FODEX project.

Here's hoping for some results that will let us add up the numbers and start to stay with some certainty what the carbon cost of logging in the tropics is, whilst also identifying areas at risk from total deforestation before it even happens.