Afromontane Fire is a Novel, Transformative, and Human-driven Disturbance

Tropical alpine environments are some of the most sensitive areas in the world to climate change. The effects of climate change are already apparent in African montane environments as glaciers have significantly retreated and recent droughts, fires, and floods have impacted local communities and ecosystems. The short duration of observational records limits our ability to test whether these disturbances result from natural climate variability or human activity. We used lake sediment cores spanning the last 12 ka from the Rwenzori Mountains, Uganda-D.R.C., to test relationships between fire regimes, vegetation, and climate at two distinct elevations. At mid-elevations, fire activity is suppressed during the warm, wet African Humid Period, but increases with drying and cooling over the late Holocene. At 2 ka, fire abruptly increases triggering a sudden shift to a grass dominated ecosystem, most likely as a result of human ignitions associated with the Iron Age in Africa. At high elevations, despite recent large-scale destructive fires, there is no evidence for local fire over the last 12 ka until the 21^st century, implying that fire is novel disturbance in the afroalpine zone. Our results show humans, rather than climate, are a major driver of afromontane fire likely through their control on ignition and as result, changes in fire regimes can cause dramatic ecosystem transformation. Thus, the creation of management plans for these unique ecosystems which focus on prevention of human ignitions are critical for these unique ecosystems, especially in the context of future climate change.