New study shows that tree dieback affects the climate change mitigation potential of a dry afromontane forest in northern Ethiopia
Tropical forests play a critical role in climate change mitigation by balancing atmospheric carbon fluxes. However, dry forests are susceptible to dieback under conditions of increased temperature and extreme climatic events such as drought, which affects their potential to provide ecosystem services. Although deforestation is severe in the Ethiopian highlands, some remnants of dry Afromontane forests still exist. However, the resilience of these forests under climate change scenarios is less known. A study was undertaken to investigate the current extent of forest degradation due to climate change, as well as quantify the effects of tree dieback on aboveground carbon stock and the carbon sequestration potential.
The study was undertaken in the Desa’a dry afromontane forest located in the semi-arid agro-ecological zone of northern Ethiopia. The study area lies in the transition zone between the Acacia-Commiphora woodland and shrubland in the Afar lowlands at an altitude of 1400 metres, and the dry evergreen afromontane forest and grassland complex in the Tigray highlands at an altitude of 2800 metres. The forest is dominated by Juniperus procera (African pencil-cedar), and Olea eruopaea (African olive), which are the foundation tree species for the study forest.
“Results from the study revealed that both J. procera and O. eruopaea species constitute about 67% of the total tree population. Tree dieback affected 25% of the total tree population. The impact on environmental health might be long-lasting, as more than 90% of dead trees belong to foundation tree species whose growth rate is slow,” said Mulegeta Mokria, a PhD student of both the World Agroforestry Centre in Nairobi, and the Institute of Geography of the Friedrich-Alexander-Unversity in Germany.
“Further results indicate that both J. procera and the O. europaea alone stored more than 90% of carbon in the forest with carbon stocks. From the total estimated carbon stock, snags contributed 34.5% which considerably affects the climate change mitigation potential of the forest,” added Dr. Ermias Betemariam, a scientist at the World Agroforestry Centre.
“Our tree ring analysis showed that trees reach medium-sized stem diameter of 20 to 25 centimetres after no less than 100 years, which implies that the forest dieback considerably affected carbon sequestration potential of the forest. This effect of forest dieback on carbon sequestration and ecosystem function is long-lasting and poses a challenge to rehabilitation interventions,” remarked Dr. Aster Gebrekirstos of the World Agroforestry Centre.
The results provide information on the magnitude of tree dieback and its long-lasting impact on climate change mitigation potential of a dry Afromontane forest. Evidently, the results substantiate the importance of restoring and reducing further anthropogenic pressure on such tree-scarce dry Afromontane forests to sustain the ecosystem services and to reduce efforts and cost for forest restoration after major loss.
“Furthermore our methodological approach, combining tree ring analysis with other aboveground biomass estimation techniques, is a reliable and cost effective means to evaluate terrestrial carbon balance. We recommend it to similar studies as well as national or international initiatives, such as the REDD+ and Clean Development Mechanism which are designed to mitigate and adapt climate change impacts,” Dr. Gebrekirstos concluded.
Download the full paper here.
Mokria, M., Gebrekirstos, A., Aynekulu, E., and Brauning, A. Tree dieback affects climate change mitigation potential of a dry afromontane forest in northern Ethiopia. Forest Ecology and Management 344 (2015) 73-83.
The lab work for this study was undertaken at the World Agroforestry Centre’s Dendrochronology Lab