BIOTROPICA 39(2): 153–160 2006 10.1111/j.1744-7429.2006.00257.x Upland Soil Charcoal in the Wet Tropical Forests of Central Guyana David S. Hammond 1 NWFS Consulting, 4050 NW Carlton Court, Portland, OR 97229, U.S.A. Hans ter Steege Institute of Environmental Biology, Section Plant Ecology and Biodiversity, Utrecht University, Sorbonnelaan 14-16, 3584 CS Utrecht, The Netherlands Klaas van der Borg Department of Physics and Astronomy, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands ABSTRACT A soil charcoal survey was undertaken across 60,000 ha of closed-canopy tropical forest in central Guyana to determine the occurrence, ubiquity, and age of past forest fires across a range of terra firme soil types. Samples were clustered around six centers consisting of spatially nested sample stations. Most charcoal was found between 40 and 60 cm depth with fewest samples yielding material at 0–20 cm depth. The first core yielded charcoal at most stations. Charcoal ages of a random subsample ranged from less than 200 YBP to 9500 YBP with a noticeable peak between 1000 and 1250 YBP. Results reinforce a view that most closed-canopy tropical forests in eastern Amazonia have been subject to palaeo-fire events of unknown severity with a peak in charcoal age consistently appearing between 1000 and 2000 YBP. The two samples dated to the early Holocene represent some of the oldest indicators of paleo-fire known from upland Neotropical forest soils. Ubiquitous soil charcoal in central Guyana further indicate both forest resilience to fire and the widespread propensity for regional forests to burn, particularly during anomalous periods of drought. Key words: disturbance history; El Ni˜ no-Southern Oscillation; Guiana Shield; fire; Precambrian; radiocarbon. RADIOCARBON DATING IS INCREASINGLY EMPLOYED IN THE NEOTROPICS as a proxy for detecting palaeoclimatic change (Soubi´ es 1979, Santos et al. 2000) and to anchor both palynological profiles and artifactual evidence of prehistoric human occupation (Dille- hay 2000, Lavall´ ee 2000). Our current knowledge of paleo-fire events in the Neotropics, whether attached to artifactual evidence of human activity or not, is largely restricted to charcoal radiocar- bon dates obtained from terra firme situated in regions dominated by thick Tertiary and Quaternary sediments, such as the Amazon Downwarp (Piperno & Becker 1996, Francis & Knowles 2001), the Llanos (Venezuela and Colombia), and Central America (Horn & Sanford 1992, Piperno 1994). In particular, charcoal derived from lake and swamp sediments have been employed, often in tandem with palynological or phytolith data (e.g., Haberle & Ledru 2001). Records of radiocarbon-dated charcoal from shallower sedi- ment facies interspersed atop Precambrian Shield regions are few by comparison. Several studies from the Brazilian Shield region have been carried out at or near its northern (e.g., Soubi´ es 1979) and southern (Vernet et al. 1994, Boulet et al. 1995) margins, but dates from the interior of the Guiana Shield, an expanse of largely Pre- cambrian crust wedged between the Orinoco and Amazon rivers, are relatively sparse (see Hammond 2005c). The only published radiocarbon dates of deposits beneath terra firme forests in this re- gion come from the upper Rio Negro district (N = 37) (Sanford et al. 1985, Saldarriaga & West 1986), at Nouragues in northern Received 8 March 2006; revision accepted 21 May 2006. 1 Corresponding author; e-mail: dhammond@nwfs.biz French Guiana (Tardy et al. 2000), the Gran Sabana in southeast Venezuela (F¨ olster 1992), and a pair of preliminary dates obtained in north central Guyana (Hammond & ter Steege 1998). Highland peat formations commonly forming in the Pantepui region of the Venezuelan Guayana have also been dated, but do not complement existing lowland site information given the contrasting environ- mental conditions and nature of carbon-dated material (Schubert & Fritz 1985). Charcoal fragments ranging in size from several milligrams to over 250 g are a common constituent of most deep forest soils in central Guyana (van Kekem et al. 1996). In particular, soils that typify many of the gently sloping landscapes of the regions consistently yield charcoal. These include soils with relatively high sand content, typically classified as Ferrasols, Acrisols, Arenosols and Podzols (sensu FAO 1998). This paper presents charcoal radiocarbon data collected for the first time from these soil types across a 60 km 2 swathe of closed-canopy tropical forest in central Guyana. METHODS STUDY AREA.—The Mabura Hill region of central Guyana (5 o N, 58 ◦ W; elevation 50–200 m asl) lies between the Essequibo and Demerara rivers. The region receives 2400–3000 mm of rainfall annually and records indicate a mean annual temperature of 25 ◦ C. Most rainfall occurs from May to August and November to Decem- ber, though monthly rainfall rarely drops to less than 60 mm per month during the intervening periods. The exception to this wet tropical climate occurs during severe warm phases of the Southern C  2007 The Author(s) Journal compilation C  2007 by The Association for Tropical Biology and Conservation 153