Paleofire history of the Falkland Islands over the last 15,000 years

Background/Question/Methods

Peat-forming grasslands that blanket the Falkland Islands face a future of predicted temperature increases and shifting precipitation patterns which may jeopardize conservation and restoration efforts. The Falkland Islands are a treeless biodiversity hotspot in the South Atlantic dominated by coastal tussac grasslands and acid grasslands in the interior that have been grazed by non-native herbivores for over two centuries. Lightning strikes and humans are known sources of fire in the contemporary Falkland Islands, but little is known about the pre-European fire history of these grasslands, despite their importance as critical breeding habitat and as extraordinary peat forming communities. To develop a baseline understanding of the fire regime over the past 15,000 years, we examined charcoal records from six peatlands in the Falkland Islands, a composite to reconstruction of the regional fire history, and identify abrupt transitions in fire trends using change point detection. We further compare our Falkland Islands fire history to Southern Hemisphere composite records for Patagonia, South America, and Australia/New Zealand.

Results/Conclusions

At individual sites, statistically significant peaks in charcoal accumulation rates occurred throughout the Holocene. The estimated mean fire return intervals varied across sites ranging from 259-452 years. A composite analysis indicated that biomass burning was the lowest during the late Pleistocene (15,000 to 13,000 years ago cal. BP) and increased during the transition to the Holocene. Biomass burning peaks centered in the mid Holocene are consistent with global grassland fire regimes, and then declined ca. 5,000 years ago to the lowest levels during the Holocene. We identified a significant change point in the composite analysis ca. 1,000 years ago, suggesting a recent, widespread shift in biomass burning that exceeds burning over the last 15,000 years and coincided with enhanced westerly wind flow. The composite Falkland Islands fire record contrasts with composite records of charcoal influx from Patagonia and other South American grasslands and savannas, despite geographic proximity. A lack of coherency with other Southern Hemisphere composite records and variability across sites suggests that local-scale factors may be important in driving local fire patterns, or a combination of local and regional-scale drivers of the Falkland Islands fire history.