SP2: Biodiversity Impacts: landscape-scale restoration dynamics in western Rwanda

Tobias Kuemmerle

Joern Fischer

Ping Sun

Matthias Baumann

Rwanda is restoring vast areas of land as part of the Bonn Challenge. As patches of restored sites are expanding throughout the country, dynamic landscape change will alter the spatial composition of woody vegetation and through this, influence the context and connectivity, as well as the trajectory of restored sites. Site-level changes, in turn, will influence the ecological functions of their surroundings. To advance the currently limited knowledge on the relative importance of different mechanisms underpinning these changes, this sub-project will identify spatiotemporal dynamics of restoration-related landscape change across the entire study area. To examine how tree cover in western Rwanda has changed through time, and how this might explain present-day ecosystem processes and biodiversity patterns, we will use satellite imagery to reconstruct landscape change for the past 35 years. The work will entail four major steps: First, we will quantify changes in tree cover over time, including a differentiation between Eucalyptus versus other types of tree cover. 
Bildschirmfoto 2023-10-30 um 16.24.18Bildschirmfoto 2023-10-30 um 16.24.57

Second, drawing on these maps, we will calculate connectivity indices through time for individual woody vegetation patches as well as for the entire landscape. This, in turn, will generate measures of landscape context for each site, as well as predictions of (a) particularly well-connected and therefore species-rich sites, versus (b) poorly connected sites which should be relatively species-poor. Third, we will test these predictions using the empirical data from sub-project 1 of our research unit. Fourth, we will return to the tree cover data in order to calculate spatially-explicit remote-sensing based indices of ecosystem functioning for the entire study area, and to quantify differences in functioning between restored and non-restored sites. Given the global proliferation of large-scale restoration initiatives, it is important to better understand how ambitious tree planting influences landscape context, connectivity, biodiversity patterns and ecological functioning at a landscape scale. Because of Rwanda’s ambitious restoration efforts, the country provides an exciting opportunity to advance knowledge about how ongoing changes in land cover and connectivity shape ecosystems. This sub-project thus makes contributions to the fields of landscape ecology and restoration ecology. In addition, this sub-project will benefit the research unit as a whole by generating an important spatiotemporal understanding that is useful for all other sub-projects.

Expected results

• Different time periods correspond to distinct types and patterns of tree cover loss and/or restoration.

• Time series of tree cover can be used to identify sites with high immigration credit.

• Current “bright spots” in vegetation structure and diversity coincide with connected restoration sites.

• Restored sections of the landscape have higher ecosystem functioning relative to unrestored, but otherwise similar sections of the landscape.