A practice-led assessment of landscape restoration potential in a biodiversity hotspot

Effective restoration planning tools are needed to mitigate global carbon
and biodiversity crises. Published spatial assessments of restoration
potential are often at large scales or coarse resolutions inappropriate
for local action. Using a Tanzanian case study, we introduce a systematic
approach to inform landscape restoration planning, estimating spatial
variation in cost-effectiveness, based on restoration method, logistics,
biomass modelling and uncertainty mapping. We found potential for biomass
recovery across 77.7% of a 53,000 km2 region, but with some natural
spatial discontinuity in moist forest biomass, that was previously
assigned to human causes. Most areas with biomass deficit (80.5%) were
restorable through passive or assisted natural regeneration. However,
cumulative biomass gains from planting outweighed initially high
implementation costs meaning that, where applicable, this method yielded
greater long-term returns on investment. Accounting for ecological,
funding and other uncertainty, the top 25% consistently cost-effective
sites were within protected areas and/or moderately degraded moist forest
and savanna. Agro-ecological mosaics had high biomass deficit but little
cost-effective restoration potential. Socio-economic research will be
needed to inform action towards environmental and human development goals
in these areas. Our results highlight value in long-term landscape
restoration investments and separate treatment of savannas and forests.
Furthermore, they contradict previously asserted low restoration potential
in East Africa, emphasising the importance of our regional approach for
identifying restoration opportunities across the tropics.