Understanding the carbon implications of deforestation, tree-planting, and changes in agricultural practices can help policy makers and land-use planners make decisions that mitigate climate change. Measuring carbon density accurately in the field is difficult and time consuming, especially in landscapes with multiple and changing land uses.

So scientists from the Center for International Forestry Research (CIFOR), University of Helsinki and Simosol have developed a new tool for estimating the amount of carbon over time in these kinds of complex, dynamic landscapes. Markku Larjavaara from the University of Helsinki led the design process for the tool and has described it in a new paper. In an interview with Forests News, Larjavaara spoke about the potential, limitations and uses for the tool.

What is CarboScen?

The name CarboScen comes from ‘carbon’ and ‘scenarios’. ‘Carbon’ refers not to carbon dioxide but to ecosystem carbon, which is stored in the biomass and soil. ‘Scenario’ refers to future land-use scenarios.

It’s a relatively easy tool to understand quite quickly. We developed it initially for some participatory workshops in which people were thinking about what could happen to the landscapes they know. They wanted to figure out how land use will change in the future, and calculate the carbon implications of those changes. And that’s what CarboScen helps us to do.

It’s also optimal for quick computations to estimate whether there is potential for carbon conservation projects, for example under the framework of REDD+. There are some existing carbon simulation models but they are very different to ours – this is new approach.

What problem is it designed to solve?

It’s important to know how much carbon there is in the ecosystem because if it wasn’t in the soil and trees, it would be in the atmosphere, and would contribute to climate change – carbon has to be somewhere.

If there’s a patch of old-growth forest in a steady state, it’s quite easy to find out how much carbon there is. If you know the carbon density – how much carbon per hectare – you just multiply it by the area. It’s relatively easy, you could do it while standing in the forest with a smart phone.

But CarboScen was developed for cases when land uses are changing.

In that situation there are two things which it make it more difficult to calculate the amount of carbon. One is that land uses don’t usually change suddenly: every year there is some change. So if you are looking at ten land uses over a period of 50 years, it is quite difficult to quickly figure out how these changes together will influence the whole landscape.

The other complication is that even when land use does change quickly, the change in the carbon density might happen much more slowly. When farmland is reforested, for example, it could take more than a century before the trees are close to their full size. To take this into account is not something that can be done in one’s head. You need something more than just the simple calculator in a smart phone – you need to sit down and use CarboScen.

What are the limitations of this tool?

You have to remember that all models are simplifications – they simplify reality.  So the results you get from CarboScen will be wrong, in a way – they are just estimates. But as statisticians say: “All models are wrong, but some are useful.” So we hope it will be useful.

It’s one additional approach – another tool in the toolbox – and it could be the first tool that the person takes out. CarboScen probably isn’t precise enough for calculating the official carbon densities for use in determining financial compensation under a REDD+ scheme, for example, but it could be used by those wishing to get compensation to quickly check whether there is potential, and whether the scheme would make sense for them.

CarboScen gives you a reasonably accurate working estimate. But more careful studies would need to be done later if financial compensation is involved.

In what situations do you see it being most useful?

I believe it is very useful in many situations, both for arriving at realistic numbers, and for understanding carbon dynamics better. It’s especially useful in landscapes where there are many land uses, and slow changes in carbon density after a change in land use, for example in the soil or because trees are growing slowly.

Applied scientists working with policy makers could use the tool to check the carbon implications of deforestation and of establishing plantations of oil palm or timber or tea in a particular landscape. They could compare several scenarios and see how the carbon densities would play out over time.

It can also be used for teaching university students or policy makers about ecosystem carbon. If someone has clear in his or her mind this idea of carbon density and how fast that changes when  there is a shift in land use– the two variables that are set in CarboScen – it’s a useful base for understanding carbon dynamics in changing landscapes. That’s one objective of having models in science: they teach us about reality.

One way to think about carbon is in terms of fluxes or flows, when carbon is running from one pool to another. That’s the natural approach when thinking about fossil fuels – oil is pumped from the Persian Gulf and it ends up in your car, and as it’s burned the carbon travels from the fossil fuel pool into the atmosphere, where it contributes to climate change.

But that has caused confusion when thinking about ecosystem carbon. In this context, talking about emissions is more difficult as carbon stored in logged trees is not straight away emitted into the atmosphere, so understanding these processes is more challenging.

I prefer to think about something concrete, something that is easier to comprehend: stocks, or reservoirs of carbon stored in the trees and soil. CarboScen is based on that approach: finding out how much carbon there is in a certain pool at a point in time.