Technology shows importance of big trees in meeting climate targets

The British Ecological Society has recently published a paper which gives interesting new insights into the specific value of large trees to the UK’s carbon sink. It draws on a study based in Wytham Wood near our HQ in Oxford – a diverse site including ancient woodland.

The study utilized laser scanning techniques to estimate the biomass carbon of living trees in this temperate forest.  Most previous calculations have relied on measurement of trees that have been felled and, for reasons of practicability, have tended to be based on smaller and medium sized trees. Estimates for taller specimens were extrapolations with constant ratios assumed – as assumption which this recent empirical work has shown to be erroneous.

The exciting new discovery is that it turns out the older assessments significantly underestimate the carbon stored in taller trees. Put simply, taller older trees tend to be denser and thus store proportionately more carbon than smaller trees – by around 70-80% more. So, every large tree that is felled, risks releasing a much greater amount of carbon than previously thought. Add in changes to forest management since the 60s which mean we have a higher proportion of larger trees and the fact that non tropical forests in the Northern hemisphere are of increasing importance as the tropical terrestrial sink declines, it is clear that the preservation of large trees needs to be given even higher priority.

“Every large tree that is felled, risks releasing a much greater amount of carbon than previously thought”

Sadly the findings make the unstoppable advance of Ash dieback even more tragic – as we expect to lose up to 80% of the third most common tree in Britain, a tree which can grow to 35 meters and live for 400 years. This reminds us that we need not only to plant and nurture trees that will grow tall and live long, but we must also ensure resilience through the strength of diversity.

And importantly in a world of carbon trading and simple number counting, the study highlights once again just how complicated it is to make estimates of carbon capture with integrity. Encouragingly, as we know from our projects at ITF and use of techniques such as GPS monitoring of trees planted, new technologies can really help us get it right. But nothing beats the right tree in the right place.

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