The carbon in blue gums

Researchers and landscape managers now have an accurate way to estimate the carbon held in blue gums (Eucalyptus spp.). Using improved allometric biomass equations along with simple tree measurements as variables, practitioners can figure out landscape-level carbon in eucalyptus-dominated landscapes with around 95% accuracy. This is expected to facilitate the greater participation in carbon markets of smallholder farmers growing gum trees on their farms – whether on boundaries, in woodlots or scattered in homestead fields.

“Smallholder farmers in developing countries are among the most efficient sequesterers of carbon,” said Shem Kuyah, Research Fellow with The World Agroforestry Centre (ICRAF) and lead author of a journal article describing the findings.

As part of the Carbon Benefits Project and with support from local farmers, Kuyah and partners randomly selected 48 eucalyptus trees from a 100-km2 site along the Yala River basin in Western Kenya. After measuring tree height, diameter, crown area and wood density, they determined the total biomass stored by the stems, branches and leaves and entire root system of each tree. From these, they developed an equation based on the diameter of the trunk measured while standing (diameter-at-breast-height, or DBH) to predict the above-ground biomass and total tree biomass of eucalyptus trees, with over 95% accuracy.  

Native to Australia, eucalyptus trees are popular among farmers in East Africa for their timber, poles, building material and fuelwood, while plantations of the trees supply the sawmilling, pulp and charcoal industries. The researchers calculated that roughly 11.7 tonnes of carbon per hectare would be lost if areas dominated by these species were to be converted to other land use.

The new allometric equations for Eucalyptus build on previous work by Kuyah and partners that developed similar equations for mixed tree species, taking into account a range of species, structural characteristics, management practices and climatic conditions found across agricultural landscapes.

Their research emphasized that tree roots are an important carbon pool – making up more than 20% of total tree biomass. “Tree roots act like carbon storage units, but they also transfer carbon directly into the soil when they decompose,” explained Catherine Muthuri, a research scientist with ICRAF who co-authored the article. “Seemingly small differences between carbon estimates using our equations and those previously available can add up to a large amount of carbon when you’re looking at a landscape,” she adds. Climate change initiatives such as Reducing Emissions from Deforestation and Forest Degradation (REDD) – increasingly focus on carbon across entire landscapes, rather than just forests.

Before smallholder farmers can receive any monetary benefit from carbon markets, it is necessary to measure, monitor and verify just how much carbon is stored in their trees. Up until now, this has been a problem in complex agricultural landscapes, largely due to the range of tree species and management techniques present. The robust generic equations for agricultural landscapes that Kuyah and partners have developed can help overcome this challenge.

“It is crucial that we get these techniques for measuring biomass right so that we can confidently assess the carbon stored on agricultural lands,” said Kuyah. “The equations we have developed for eucalyptus and mixed species are a first step in providing the level of accuracy needed for farmers to participate in REDD+ and similar payments for environmental services schemes.”

“Our next step is to calibrate these equations so that they can be applied across different landscapes. By using approaches such as fractal branch analysis – which combines a model with measurements of tree branches and stems – we can do this without the need to fell any trees,” said Kuyah.


The research Allometry and partitioning of above- and below-ground biomass in farmed eucalyptus species dominant in Western Kenyan agricultural landscapes
won the award ‘Outstanding Paper’ at the International Conference on Sustainable Forest Management – The 2nd Forest Science Forum, hosted by the Chinese Society of Forestry and Beijing Forestry University in Beijing, China in October, 2012.

Links to the Journal Articles

Allometry and partitioning of above- and below-ground biomass in farmed eucalyptus species dominant in Western Kenyan agricultural landscapes

Allometric equations for estimating biomass in agricultural landscapes: I. Aboveground biomass

Allometric equations for estimating biomass in agricultural landscapes: II. Belowground biomass

Crown area allometries for estimation of aboveground tree biomass in agricultural landscapes of western Kenya

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