Talk Roadless space is greatly diminished by logging in intact forest landscapes of the Congo Basin

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? Intact forest landscapes can be conserved by retention of “roadless space”, a concept based on distance to the nearest road from any point. We developed a novel use of the empty space function – a general statistical tool based on stochastic geometry and random sets theory – 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 temporal development of roadless space in certified and non-certified logging concessions inside and outside areas declared as IFL in the year 2000. 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. Between 1999 and 2007, rapid road network expansion led to a marked loss of roadless space in IFL. After 2007, this trajectory levelled out in most areas, due to an equilibrium between newly built roads and abandoned roads that became revegetated. However, concessions within IFL that have been certified by FSC since around 2007 showed continued decreases in roadless space, thus reaching a level comparable to all other concessions. Only national parks remained mostly road-free. The established concessions outside IFL even showed a slight increase in roadless space due to forest recovery on abandoned roads. 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. We suggest the empty space function as a viable method to calculate roadless space. We identified the highest fragmentation-effect resulting from a new public road corridor that is crossing the Congo Basin forest on a south-north axis. We point out the urgent need for measures to guarantee ecological corridors between protected areas and remaining intact forests. Logging concessions might play a key role in conserving forest connectivity by controlling road access and maintaining crossing facilities.

Road network density, empty space function, random sets, road impact persistence, sustainable forest management