Spatiotemporal assessment of deforestation and forest degradation indicates spillover effects from mining activities and related biodiversity offsets in Madagascar

Mining has severe environmental and social impacts. To compensate for the environmental damage caused at mining sites, mining companies are required to engage in biodiversity offsetting activities elsewhere. In forest landscapes, most offsetting policies focus on compensating for biodiversity loss from deforestation, while forest degradation is largely ignored – even though it contributes substantially to biodiversity loss. One reason for this is that forest degradation is challenging to assess and monitor. This study focuses on a large nickel and cobalt mine in Madagascar. By analysing remote sensing time series, we assess detailed annual forest change dynamics and distinguish different types of forest disturbance within and around the mining lease area and the two main associated biodiversity offset areas between 2006 and 2020. Our results show that deforestation rates within the two biodiversity offset areas are low (18 ha, or 0.4%; 164 ha, or 2.4%), suggesting that conservation measures are effective. However, this is not the case when looking at forest degradation. We found that substantial shares of forest within the two biodiversity offset areas are affected by degradation (545 ha, or 11.4%; 662 ha, or 9.7%). In the surrounding unprotected landscape, the rates of deforestation (451 ha, or 6.7%; 553 ha, or 4.9%) and forest degradation (2360 ha, or 34.8%; 5794 ha, or 51.1%) are much higher. The spatiotemporal pattern indicates spillover effects for both deforestation and forest degradation. Taken together, our findings show that restrictions on local communities' access to forest resources within biodiversity offset areas affect the surrounding landscape and can cause substantial additional adverse environmental impacts there. We also demonstrate that forest degradation monitoring is feasible, and that forest degradation is widespread even though it is still largely ignored. These findings should be considered in future biodiversity offsetting policies and best practices.