Roadless space and logging in intact forest landscapes of the Congo Basin

Background: Forest degradation in tropical regions is often associated with roads built for selective logging. Forest areas that are not accessible by roads are considered valuable because they provide habitat that is not immediately impacted by major human activities. The protection of such Intact Forest Landscapes (IFL) is high on the biodiversity conservation agenda, leading to a motion of the Forest Stewardship Council (FSC) to better protect IFL in certified forest concessions. However, in many parts of Central Africa logging takes place at very low intensities and most roads are abandoned after few years of timber harvesting. Taking limited road persistence into account we asked: How did road networks in FSC certified concessions affect IFL? Methods: Intact forest landscapes can be conserved by retention of “roadless space”, a concept based on distance to the nearest road from any point. We used the Empty-Space Function, a general statistical tool from stochastic geometry, to calculate roadless space based on time series of LANDSAT images. We followed the spatial and temporal dynamics of logging roads in a part of the Congo Basin that has recently seen rapid expansion of road networks for selective logging. We compared the development of roadless space in certified and non-certified logging concessions inside and outside areas declared as being IFL in the year 2000. Results: The persistence of logging roads was limited over time, with only 12% of the overall network being permanently open. However, also taking only actively used roads into account, roadless space inside IFL has decreased rapidly due to expansion of logging into previously unlogged areas. Concessions that are now certified by FSC showed a slower rate of decrease before certification but after that their roadless space decreased to a level comparable to non-FSC concessions. The established concessions outside IFL showed a slight increase in roadless space due to forest recovery on abandoned roads. Conclusions: We recommend that forest management should make the preservation of large connected forest areas a top priority by effectively monitoring - and limiting – the occupation of space by roads that are accessible at the same time. Given the strong dynamics in road detectability, we challenge the static definition of intact forest landscapes based on a buffer around any road ever detected. Instead we suggest the empty space function as a viable alternative to calculate roadless space. (Texte integral)