Researchers have called for the planting of more Alnus trees in order to reduce manmade carbon emissions and offset the impact of climate change in Rwanda.
The researchers said the plant, common among households, was effective in sequestering carbon—the process of stopping carbon dioxide from escaping into the atmosphere.
However, the report says that its sustainability was under threat.
The findings come at the time Rwanda aims to reduce emissions of carbon dioxide by 4.6 million tonnes by 2030 through various measures.
The country partly looks to agroforestry to play a key role in sequestration, restoration of degraded landscapes and promoting sustainable agriculture.
A study carried out in north-western Rwanda indicates that planting fast-growing Alnus trees on farms contributes significantly to sequestering carbon but this varies with the age of the tree and the altitude.
The researchers measured the biomass of 1767 Alnus trees on 84 farms at 2011–2634 metres above sea level.
Their study known as "potential of Alnus acuminata based agroforestry for carbon sequestration and other ecosystem services in Rwanda” focused on trees planted between 2009 and 2018.
Athanase Cyamweshi, the lead author of the study published in the scientific journal, Agroforestry Systems, noted that their findings confirmed that the amount of carbon in the trees’ biomass increased with age.
Trees aged 5 years and older were found to sequester more carbon than younger trees.
However, the study has found that practices, such as pruning (trim (a tree, shrub, or bush) by cutting away dead or overgrown branches or stems), coppicing (cut back (a tree or shrub) to ground level and pollarding (cut off the top and branches of a tree) by farmers to derive various tree products and also reduce competition with crops, adversely affected Alnus’ capacity to capture and store atmospheric carbon.
The study team recommended growing a diverse range of tree species on farms to ease pressure on Alnus trees so as to maintain them longer in agricultural landscapes for climate regulation and other ecosystem services.
Apart from carbon sequestration, findings from a household survey conducted during the study revealed that Alnus were mainly grown and managed for providing sticks that support the growth of climbing beans, firewood, timber, poles and fodder.
Alnus also enhances soil fertility and boosts crop productivity when incorporated in the soil as green manure, the study says.
"Through the Rural Resource Centres established under the project, we have enabled smallholder farmers to access high quality multipurpose tree-planting material, training and extension advice on appropriate tree-crop management practices,” said Catherine Muthuri, a co-author of the research paper.
The ‘Sustainable Forests and Agroforestry’ programme is one of Rwanda’s 14 programs in the green growth agenda set for 2050.
Rwanda’s current forest cover is equivalent to 30.4 per cent or about 724,662 hectares. Of these, 53 per cent are plantations, 21 per cent are wooded savannas, 19 per cent are natural mountain rainforests and 6.2 per cent are shrubs.
Currently, 23,456.15 hectares (equivalent to 38.4 per cent of state forests) are now managed by private investors through long term concession agreements.
The research team was composed of scientists from the Rwanda Agriculture and Animal Resources Development Board, World Agroforestry (ICRAF) and Jomo Kenyatta University of Agriculture and Technology.