Experimental Assessment of Tree Diversity Effects on The Restoration Success of Tropical Dryland Forests in Tigray, Northern Ethiopia

Many people are highly dependent on dryland biodiversity. For example, about 70% of Africans depend directly on dry and sub -humid lands for their daily livelihoods. Drylands present challenges to plant and animal survival, but many species have evolved with special adaptations that allow them to cope with the variable water supply. Despite their low productivity, dry tropical forests are often of vital importance to rural communities in Sub-Saharan Africa, in particular in the Horn and eastern Africa. These lands have great biological value and are home to many of the world’s food crop and livestock species. However, scientific information on ecology, vegetation development, species trait, productivity and ecosystem services, utilization and management of indigenous species are still required for proper planning and restoration of these dry land resources. On the other hand, testing the relationship between tree species diversity, productivity, and resilience in forests is difficult owing to the inability to control variables within these complex ecosystems. Hence, long-term controlled experiments of higher plant diversity is essential to study the relation between tree diversity and ecosystem functioning, a gradient of species number ranging from single-species stands to multispecies mixtures. Therefore, the overall aim of this research is to investigate the effect of tree species mixture and shading on tropical dry forest restoration success by assessing IDENT Ethiopia, a tree diversity experiment in dry Afromontane forest. The experiment is located in Mekelle University, Endayesus Campus close to the tree nursery. IDENT-Ethiopia tree diversity experiment is part of the International Diversity Experiment Network with Trees, with experiments on the American, European and now also African continent. The experiment is organized with 9 native woody species distributed over 270 plots and three blocks each with a shaded and un-shaded treatment. Within each (shaded and unshaded) treatment, gradients were created by manipulating species richness (SR) and functional diversity (FD)to test the following hypotheses: (1) Mixed forests are able to restore multiple ecosystem services under climate change, because they ensure survival of sensitive species that support crucial ecosystem functions and services. (2) Seedling survival in mixed forests is higher than monoculture forests. (3) Mixed forests are more productive compared to monocultures forest. (4) There is a positive interaction between mixture and shading because dry afromontane tree species establish more successfully in a sheltered environment than in open systems.