Professor Patricia Thornley, Director of the Supergen Bioenergy Hub, responds to Patrick Barkham’s article in The Guardian on 10 March 2020: Trees on commercial UK plantations ‘not helping climate crisis’.
There is a need to be careful with the logic used in this article. Plantation forests cover a certain land area in the UK at present. Every year they absorb carbon from the atmosphere, and that is helping to regulate climate change. When the trees are mature, they are chopped down and used (that is why they were planted in the first place). So, the first thing to realise is that the carbon that is released when those trees eventually decompose is not fossil carbon, so it is not transferring carbon that was long ago locked up from the atmosphere back to the atmosphere, thereby adding to the long-term burden. Instead it is carrying out a medium-term cycling. The carbon was absorbed over the last 15 years during growth and will now (according to the report) be released in the following years (almost immediately if used as wood fuel, up to many decades if used for construction). That does not necessarily mean that the release is exacerbating climate change. If the forest area is maintained then more carbon will be sequestered in the years while that product is used. In fact, the fastest sequestration rates are in the earlier growth years, so we actually need to chop these trees down to allow the land to be freed up to do more sequestration.
To draw a parallel with which most people will be more familiar: The plantation trees operate on a timescale that is short in comparison to the increase in carbon concentration we have seen since the industrial revolution. So, you can think of the fossil fuel oil, coal and gas reserves as being like your savings account. These are your long-term stocks that you have laid down to provide a buffer against all eventualities, and squandering those by releasing to the atmosphere will have a huge negative effect on the planet, in much the same way that raiding your savings account to pay for luxuries will have a negative impact on your financial status.
But plantations work on a shorter timescale and it makes sense to think of these as more like your current account. The account balance (carbon stock) increases as we gain income and decreases as we spend. It doesn’t matter too much how low it gets before payday as long as net over the year we remain roughly in balance and don’t go overdrawn. So it is with trees and the planet. There will always be perturbations and these can seem large if we focus in on a very small timescale or land area. But the key is to look at the long-term trend over the whole planet – that is what the atmosphere sees. And if that continues to extract each year an amount of carbon that is not that dissimilar to what is released when those trees are used, that is fine. The problems arise when the carbon stock (the long-term reserves that have been laid down by the tree growth) are affected. That is generally caused by reductions in land area under forest cover or sometimes by changes in management or climate that affect the actual standing amount of biomass in a plantation – again this needs to be viewed holistically, as different plots of land will be at different points in their overall cycle.
So, yes it is best to use trees in a way that lays down carbon long term, for example in construction, but not all trees or tree parts are suitable for that. Forestry is a business and landowners grow what they know they will be able to sell. So while we all might love to increase the broadleaf coverage in the UK, this is only going to be viable if there is a market for the wood products from long-rotation forests (so, buy more hardwood flooring and less laminate!).
I am concerned about how agricultural expansion is driving deforestation in the Amazon. That is causing loss of carbon stock (raiding our planet’s carbon savings account) and limiting our capacity to absorb carbon each year (reducing the payments into our planetary carbon current account). But I’m not worried about whether we return carbon that we removed from the atmosphere over the last 15 years in the next four, 10 or 25 years. That is like getting worried about whether my annual salary is paid weekly or monthly. It doesn’t actually matter that much in the long run as long as we do maintain the area of land that is forested and use tree species that are sensible for the location.