More than half of all plant and land animal species in the world live in tropical forests. Yet, despite their importance, deforestation is a serious environmental concern and a major source of greenhouse gas emissions. Forest cover loss has been rising steadily in the tropics over many years.
“One solution to the deforestation challenge is limiting access”, PhD candidate Mengesteab Hailu Ubuy says.
“For example by establishing exclosures.”
Exclosures are protected areas that exclude tilling, harvest of trees, and grazing by livestock, and are meant to allow natural regeneration and ecological succession to rehabilitate deforested and degraded lands.
In Ethiopia, exclosures are rapidly expanding to reverse deforestation and land degradation. Local communities, particularly in Tigray, the northernmost region, show a clear preference for exclosures. They are useful for ecosystem services such as climate regulation, biodiversity conservation, and for greening landscapes, but have also a potential for providing grasses for livestock and trees for fuelwood and construction to the local communities.
“Informed decision-making is important to ensure sustainable management of such exclosures,” Ubuy says.
Basis for informed management
Ubuy has collected data on trees and growing conditions from six exclosures in Tigray for his doctorate. They represent different locations, districts, years since establishment, and a wide range of altitudes and climatic conditions. The main objective of his thesis was to provide data, models, and insights for informed decision-making in exclosure management.
First Ethiopian database for wood basic density
Ubuy has documented wood basic density for 50 tree and shrub species from the exclosures.
“This is the first step towards establishing a wood basic density database for Ethiopia.”
The wood basic density values will be useful for forest management in Ethiopia, e.g. for characterizing wood properties such as fuelwood quality and for estimating biomass as required for implementing the REDD+ mechanism.
“The wide wood basic density variation within and between tree species and growing conditions that we have been observed in the exclosures implies that future studies should explicitly cover more sites and different tree species to capture even more variation,” Ubuy comments.
His results will also be added to the Global Wood Density database. This database describes wood basic density for different tree species throughout the globe and includes more than 16000 entries.
Biomass loss larger than gain
Based on permanent sample plots Ubuy has developed the first models for growth, mortality and recruitment of trees in exclosures. He has also quantified biomass changes over a 2-year period from the plots. Here he applied new biomass models that he developed as a part of the doctorate.
“In average for all the plots, the net change in biomass was negative because the biomass loss from natural mortality and harvest was larger than the gain from growth and recruitment.”
Present status and prospects for a sustainable development
To evaluate the present status of the exclosures, he has used multiple indicators, such as biomass and carbon stocks, species diversity, regeneration, diameter distribution, and harvest, and information on historical background and management of the exclosures.
“Generally, their present status is adequate, and much better than if the exclosures had not been established, but the harvest taking place, which largely is illegal, is the main cause of the observed negative net change in biomass, and a threat to the prospects of sustainable development.”
To achieve sustainable management, Ubuy suggests that better guarding of the exclosures possibly can improve the situation in a short-term perspective.
“However, to secure the long-term sustainability, sound management plans that are able to balance between growth and harvest should also be in place.”
"In this way, also the local communities will benefit from harvesting of trees without violating laws and the prospects of a sustainable development in exclosures," he concludes.