Over the past decades, Rwanda has implemented a wide range of ecosystem restoration interventions. Most likely, the restoration focus in the country will shift in the future from primarily restoring ecosystem-based livelihoods to more biodiversity-focused restoration efforts. Drawing on a cross-sectional comparison of different types of restoration interventions, this sub-project will assess (1) how structure, diversity and function within restored sites change in response to time since restoration, and (2) what role the functional and taxonomic diversity of the species planted play in shaping the trajectory of restored sites. The knowledge generated can support Rwanda as well as other parts of the world in pursuing evidence-based, target-oriented ecosystem restoration that reflects changing needs and growing ambitions.

This way, ecosystem restoration can increasingly move beyond simply reducing societal impacts to the partial or full recovery of native ecosystems. Approaches to ecosystem restoration can significantly differ in terms of their effect on ecosystem diversity, structure and function. In Rwanda, four types of ecosystem restoration are commonly pursued: agroforestry, woodlot plantings, watershed protection through erosion control, and natural regeneration. The extent to which these restoration efforts are successful in restoring the diversity, structure and function of ecosystems remains largely unknown. In addition, depending on the type of restoration and shaped by priority effects (i.e., the impact of the order of species arrival at a restored site), different restored sites will likely follow different ecological trajectories. Here, we consider four possible trajectories: historical, hybrid, novel, and designed ecosystems. To evaluate the present state of a given restored site and determine its possible trajectory, we will compare species diversity, ecosystem structure and ecosystem function to reference sites of the historical or a positive contemporary ecosystem state as well as of a degraded ecosystem state.

To this end, we will assess how woody plant as well as bird species community diversity and composition change through time within different types of restored sites. Woody plants are important in the context of Rwanda because they dominate the structure, composition and function of historical and contemporary reference ecosystems in the study area, and are also the main focus of restoration activities. Birds, in turn, are involved in important ecosystem functions and are also likely to be mechanistically linked to woody vegetation composition and structure. In a final step, we will quantify a set of ecosystem functions deemed to be particularly relevant within the local context. For this, we will focus on readily measurable soil physical properties as well as on the regeneration potential of woody species.