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Biomass production using fast growing tree species presents a sustainable energy pathway for developing countries with high dependence on biomass as an energy source. A rapid land use change from cropland to short rotation forestry (SRF) using black wattle (Acacia mearnsii De Wild.) has taken place in northwest Ethiopia. The driver is the increasing market demand for charcoal in urban areas and the economic opportunities this presents for farmers. Acacia mearnsii is a fast growing, nitrogen (N) fixing tree, and native to Australia. This thesis investigated the extent of the land use change to SRF and the environmental sustainability of the SRF production system compared to the teff (Eragrostis tef (Zucc.) Trotter.) production system it replaced. The analysis was done using a combination of methods, including satellite imagery analysis, soil and biomass samples analysis, and review of data from published studies. By 2022, 60% of the fields under crop cultivation in 2005 had been converted to SRF. The landscape carbon (C) budget showed a net CO2 sink due to C sequestration in biomass. However, despite the C sequestration and N fixation in tree biomass, successive rotations had lower soil C and N stocks. Nutrient budget estimates suggest that this is likely due to mineralization of soil organic matter to mobilize organically bound phosphorus and sulfur. The SRF resulted in the export of large amounts of base cations in harvested biomass, leading to higher soil acidification compared to the teff production system. Despite these concerns in the long term, biomass production reduced the pressure on natural forest for exploitation of charcoal and firewood. The findings highlight the need for improved management practices, including retaining nutrient dense residues in the field, phosphorus and sulfur fertilization, and liming to neutralize the soil acidity.Biomass production using fast growing tree species presents a sustainable energy pathway for developing countries with high dependence on biomass as an energy source. A rapid land use change from cropland to short rotation forestry (SRF) using black wattle (Acacia mearnsii De Wild.) has taken place in northwest Ethiopia. The driver is the increasing market demand for charcoal in urban areas and the economic opportunities this presents for farmers. Acacia mearnsii is a fast growing, nitrogen (N) fixing tree, and native to Australia. This thesis investigated the extent of the land use change to SRF and the environmental sustainability of the SRF production system compared to the teff (Eragrostis tef (Zucc.) Trotter.) production system it replaced. The analysis was done using a combination of methods, including satellite imagery analysis, soil and biomass samples analysis, and review of data from published studies. By 2022, 60% of the fields under crop cultivation in 2005 had been converted to SRF. The landscape carbon (C) budget showed a net CO2 sink due to C sequestration in biomass. However, despite the C sequestration and N fixation in tree biomass, successive rotations had lower soil C and N stocks. Nutrient budget estimates suggest that this is likely due to mineralization of soil organic matter to mobilize organically bound phosphorus and sulfur. The SRF resulted in the export of large amounts of base cations in harvested biomass, leading to higher soil acidification compared to the teff production system. Despite these concerns in the long term, biomass production reduced the pressure on natural forest for exploitation of charcoal and firewood. The findings highlight the need for improved management practices, including retaining nutrient dense residues in the field, phosphorus and sulfur fertilization, and liming to neutralize the soil acidity.

Nyckelord

Acacia mearnsii; short rotation forestry; land use change; charcoal; fuelwood; carbon sequestration; nitrogen fixation; nutrient budget; soil health; sustainability

Publicerad i

Acta Universitatis Agriculturae Sueciae
2025, nummer: 2025:54
Utgivare: Swedish University of Agricultural Sciences

SLU författare

UKÄ forskningsämne

Skogsvetenskap

Publikationens identifierare

  • DOI: https://doi.org/10.54612/a.242jbn5alj
  • ISBN: 978-91-8046-563-2
  • eISBN: 978-91-8046-558-8

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/141967