Data, models, and insights for informed decision-making in the management of exclosures in Tigray, northern Ethiopia

Abstract

In Ethiopia, exclosures are rapidly expanding and performing good to reverse deforestation and land degradation. Local communities, particularly in Tigray show a clear preference for exclosures, which are useful for ecosystem services, climate regulation, biodiversity conservation, and for greening landscapes. However, informed decision-making is important to ensure sustainable management of exclosures in the future. The main objective of this thesis was therefore to provide data, models, and insights for informed decision-making in the management of exclosures in Tigray. In Paper 1, we documented wood basic density (wbd) for 50 tree and shrub species from six exclosures. This was an initiative to establish a first wbd database for Ethiopia as well as to enrich the Global Wood Density database. Using a general additive model technique, we found that tree species, tree size variables, and altitude significantly explained the wbd variation. In Paper 2, we also applied wbd as one of the independent variables to develop a first set of general multi-species biomass models for trees and shrubs of exclosures in Tigray. Using a nonlinear least square modelling technique, general, site-, and genus-specific models were developed. The general models can be applied for large parts of the exclosures in Tigray when managing them and implementing the REDD+ mechanism. Paper 3 was the first to provide results based on permanent sample plots (PSPs) from exclosures in Tigray. Growth, mortality, and recruitment models were developed and biomass changes were quantified. The biological relationships for some of the models were as expected but generally, the relationships between the independent variables and growth, mortality, and recruitment were weak. This is mainly due to the short observation period of two years and the early successional stage of the exclosures. In average for all PSPs, 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. In Paper 4, we used multiple indicators, such as biomass and carbon stocks, species diversity, regeneration, diameter distribution, and harvest to evaluate the status of the exclosures. Generally, we consider the status as appropriate but the observed illegal harvest is a threat for future sustainability. The achievement of this thesis is an important step forward to facilitate informed decision-making in the management of exclosures. However, still studies that combine ecological and socio-economic aspects, including management performance, bylaws, governance, and organizational setup are important for further improvement in the management of exclosures in Tigray.