Are traditional home gardens in southern Ethiopia heading for extinction? Implications for productivity, plant species richness and food security

•Home gardens in Ethiopia commercialize due to population pressure.•Commercialization induces an increased use of mineral fertilizer.•Recently evolved systems performed better on productivity and food security.•Commercialization does not guarantee poor farmers’ food security.•Plant species diversity was not jeopardised by the commercialization process. While home garden systems are acknowledged for their capacity of supporting a very dense population, the productivity of these systems and their contribution to food security and dietary diversity are poorly quantified. Although several articles document the decrease in species richness in home gardens due to processes of modernization, relatively little attention has been given to how the change in diversity impacted productivity. Five predominant home garden systems identified in a previous study were intensively monitored during 12 months within four districts of Sidama and Gedeo zones of southern Ethiopia. Data from 24 farms were collected on plant species, soil characteristics, crop inputs, field sizes and crop yields and livestock production. The productivity of enset for both food and feed was lowest in Enset-coffee home gardens. Barley and khat yielded significantly more per ha in Khat-based systems than in other ones. Maize and coffee productivity did not differ significantly between home garden types. Overall crop productivity was lowest in the traditional Enset-coffee systems (1820kgDMha−1) and highest in the newly evolved Enset-cereal-vegetable systems (3020DMkgha−1). Energy productivity from food crops was higher in Enset-based systems (43GJha−1) than in other systems whereas revenue was lowest in Enset-based systems (719US$ha−1) and highest in newly evolved Khat-based systems (6817US$ha−1). The rate of N application through compost explained 30% of the variability in kocho standing biomass. The rate of N application in inorganic fertilizer explained 43% and 25% of the variability in khat and barley yield respectively. There was no positive effect of plant species richness on total crop and energy productivity except for the revenue in enset-oriented systems. Khat-based and Enset-cereal-vegetable systems were more food secure than the traditional home gardens, and these newly evolved systems also did not lead to a loss in plant species richness. The modification of traditional home garden systems by introducing the high value cash crop khat and annual cereals in response to farmland constraints