Tropical Rainforest and Shifting Cultivation: Understanding the Role of Anthropogenic Fire throughout the Holocene in Tropical Rainforest in West Kalimantan, Indonesia

El Niño-Southern Oscillation-related droughts have resulted in large forest fires on Borneo multiple times in recent decades. These fires have major consequences for humans and wildlife by converting partially-cleared forest to fire-prone fern, shrub, and grass. While fire is rare in primary tropical rainforest, multiple studies have found evidence of past fire in tropical forests—including on Borneo—overturning the theory that fire is excluded as a disturbance in tropical rainforest due to high moisture. Yet, the prevalence and spatial patterns of fire in the tropical rainforests of Borneo before the modern era is not well understood. Borneo's indigenous groups have been using fire to clear land for centuries, and charcoal is abundant in low elevation, productive areas that would have been suitable for agriculture. However, charcoal is also present in steep, high elevation areas that would not have been suitable for agriculture but are more susceptible to natural fires than the humid, multi-story forests of lower elevations. Thus, fire regimes dominated by human-caused fire would likely have a different spatial occurrence of fire than fire regimes dominated by natural fire. To understand the influence of human vs. natural fires and the historical resilience of tropical rainforest to fire, as well as the role that fire plays in carbon cycling in tropical rainforest, we are using radiocarbon dating and relative abundance of charcoal in different habitat types to examine the historical pattern of fire and pyrogenic-carbon content of soils in primary rainforest in Gunung Palung National Park (Indonesia). While we found macroscopic charcoal (>2 mm) in soil cores at all sites sampled to date, charcoal was ca. six times more abundant in lowland habitats than in upland habitats. Initial calibrated radiocarbon dates (n=9) show that charcoal in lowland sites dates to ca. 0.45 ka, whereas charcoal in upland sites dates to 12.5-12.7 ka. Charcoal was also ubiquitous (present in each replicate core) in the lowland sites but not upland or peat swamp sites. Thus, while additional radiocarbon dates are forthcoming, our preliminary results suggest that land clearance was a major source of fire in Gunung Palung National Park's forest and that, unlike recent events, the forest was resilient to these earlier fires.