While raising crop yields, African thorn tree Faidherbia albida captures large amounts of carbon
A large, old Faidherbia albida tree with a metre-plus diameter stored the equivalent of the CO2 emitted by 8 cars over one year. These useful trees play an important role in carbon sequestration, a critical part of the effort to reduce greenhouse gas emissions linked to climate change.
People in many areas of Africa gain numerous benefits from the leaves, branches and trunks of the dryland thorn tree Faidherbia albida.
The tree’s spreading roots conserve the soil from wind and water erosion. Its roots fix atmospheric nitrogen which then passes to the leaves, which fertilize the topsoil when they fall, leading to higher crop yields. Faidherbia’s wide canopy provides shade as well as leaves and pods that serve as nutritious fodder for sheep and goats. And for people living around lakes, the trunk has light yet strong wood perfect for traditional dugout fishing canoes. The multipurpose tree is ideal for evergreen agriculture.
And now, carbon credits could join the list of benefits Faidherbia albida brings to communities.
Research by World Agroforestry Centre (ICRAF) and partners, reported in a recent article in the journal Agroforestry Systems, has come up with formulae that allow us, for the first time, to accurately calculate the ‘total above-ground biomass’ of F. albida. This value indicates the amount of carbon sequestered by the tree. Working out the carbon stored in trees is the starting point for entering the global carbon credits markets, in which payments are based on the amount of the carbon in standing trees.
The allometric equations for calculating Faidherbia albida biomass were developed under a collaborative effort led by Tracy Beedy, a post-doctoral researcher working under UN FAO’s Festus Akinnifesi, then regional director of ICRAF-Southern Africa, alongside Tembo Chanyenga, acting director of the Forestry Research Institute of Malawi, and co-researchers from ICRAF-Malawi and ICRAF-Headquarters.
The CGIAR’s Fund Council supported Beedy’s post-doctoral research, under a program to purposely support women scientists in agriculture.
The work took place in six regions located in semi-arid to sub-humid zones of Malawi: Bolero and Karonga to the North; Salima and Makanjila in the central-eastern area; and Bwanje and Mwanza to the South-West. The researchers sampled trees in five parkland sites (expanses of land with crops cultivated under scattered natural-growing trees), and one block planting (a plantation established by the Forestry Research Institute of Malawi in 1990).
Beedy and colleagues measured the trees’ diameters at breast height (DBH), diameters at various heights, the lengths and diameters of the trunk and all branches, and the span of the trees’ crown area (CrA). They then cut down the sample trees, and assessed their total above-ground biomass (TAGB). Using UNFCCC (2006) guidelines and mathematical modeling, the researchers were able to arrive at the allometric equations most suitable for estimating the total above-ground biomass (TAGB) stored in the F. albida trees. These are:
For block planted trees: Ln(TAGB)=−1.23+2.16×Ln(DBH)
For trees in parklands: Ln(TAGB)=−1.62+0.702×Ln(DBH)2×(CrA)
These equations can now be used to readily and accurately estimate the carbon stored in standing Faidherbia albida trees under similar conditions.
Carbon sequestration and climate mitigation
The size, age and location of tree affected how much biomass it stored; the biomass in trees from the block planting ranged from 0.012 to 0.630 Mg per tree while that of parkland trees ranged from 0.2 to 12.3 Mg/tree. This translates to between 367 kg and 22.6 tons of atmospheric carbon (or CO2) per Faidherbia tree.
As such, at 22.6 tons CO2 sequestered, the largest tree sampled—an old parkland Faidherbia with a girth of 116 cm diameter at breast height— held the equivalent of the CO2 produced by 8 medium sized cars for one year (an average car produces around 2.8 tons of CO2 per year).
Beedy says the large amounts of carbon stored in F. albida “demonstrates the important role played by these trees in carbon sequestration, a critical part of the effort to reduce greenhouse gas emissions linked to climate change.”
Worldwide, many initiatives on climate change mitigation are promoting the planting and maintenance of trees in landscapes, as part of the long-term goal of keeping global warming to below 2°C above pre-industrial levels.
Mechanisms such as Green bonds issued by the World Bank and others finance carbon sequestration programs, with the money going to support climate mitigation and adaptation projects in developing countries, including on farmlands.
Beedy and co-authors note that were Malawi to enter this market, payments for carbon (carbon credits) for Faidherbia albida could become one more incentive for farmers to keep these valuable agroforestry trees on their farms and parklands.
But they are quick to note that carbon has never been part of the average Malawian farmer’s motivations for keeping msangu, the local name for Faidherbia albida. In fact, at Bolero, Beedy’s team had to obtain special permission from the local leadership to fell seven of these trees for research; the traditional authority there he had instituted a civil ordinance against cutting msangu , as it was so important as a source of soil fertility for maize crops.
“Faidherbia albida trees are a smart option for the farmer. That they are also climate-smart is a welcome bonus,” says Tembo Chanyenga of the Forestry Research Institute of Malawi.
For further information, contact:
Tracy Beedy, PhD, Area Research and Extension Specialist, Oklahoma Panhandle Research and Extension Center, Goodwell, Oklahoma
Download research paper by Beedy TL, Chanyenga TF, Akinnifesi FK, Sileshi GW, Nyoka BI, Gebrekirstos A. 2015. Allometric equations for estimating above-ground biomass and carbon stock in Faidherbia albida under difference management systems in Malawi Agroforestry Systems.
Download booklet: Farming trees, banishing hunger. How an agroforestry programme is helping smallholders in Malawi to grow more food and improve their livelihoods
Presentation by Godfrey Khundlande and Isaac B. Nyoka: Landscape Restoration in Southern Africa
Beating Famine conference site: http://beatingfamine.com/
Functional branch analysis (FBA), a theoretical model of tree branching architecture, is one promising non-destructive alternative for tree biomass equation development. See: MacFarlane DW, Kuyah S, Mulia R, Dietz J, Muthuri C, van Noordwijk M, 2014 Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture.
Dr. Kuyah has also been working on methods to quantify carbon stocks efficiently in Africa. See Quantifying tree biomass carbon stocks and fluxes in agricultural landscapes.
S Kuyah, C Mbow, GW Sileshi This chapter presents methods to quantify carbon stocks and carbon stock changes in biomass of trees in agricultural landscapes. Specifically it assesses approaches for their applicability to smallholder farms and other tree enterprises in agricultural landscapes.