15 From the Margins to the Deep: A Tribute to the Science and Art of A. Conrad Neumann

Friday, 20 March 2020
1:30 PM - 5:30 PM
Lake Fairfax

FIRE HISTORY IN DEVONSHIRE MARSH, A HOLOCENE RECORD OBTAINED FROM A CORE TAKEN BY A. CONRAD NEUMANN

Paper number: 15-3
Program: Symposia Sessions
Time: 2:10 PM – 2:30 PM

Authors

Abstract

Using a 1035 cm core taken by A. Conrad Neumann from the peats of Devonshire Marsh, Bermuda, analysis of palynomorphs and charcoal preserved within provides insight to the history of vegetation and fires in the marsh. This core, having a basal date of 7200±120 14C yBP was used in constructing a sea level curve for Bermuda by Neumann (1972). High-resolution sampling (5 cm) in the upper 200 cm of this core provides a record of anthropogenically induced fires on the island since colonization in 1609. Charcoal particles are only found in quantity above a depth of 120 cm and support an interpretation that fires in this part of the island are anthropogenic in origin.

Prior to colonization, dominant arboreal taxa in Devonshire Marsh included Sabal bermudana, Juniperus bermudiana and Myrica cerifera with an understory of ferns and sedges. Little change in pollen spectra is noted below a depth of 115 cm. With the charcoal horizons indicative of first major fire in the marsh at this depth, the arboreal taxa in the pollen spectra show marked decrease with a coincident rise in spores of the ferns Osmunda cinnamomea, Woodwardia virginca and Thelypteris kunthii. In the upper 60 cm, loss of shade is noted by the presence of spores of the open-ground fern Pteridium aquilinum.

The largest accumulation of charcoal particles is found at depths of 110 and 115 cm. Sediment accumulation rates based on 14C dates place this charcoal horizon at approximately 500 yBP. This deposit apparently represents fires deliberately set all over Bermuda in 1616 to eliminate a plague of rats that began in 1614. Charcoal is also found in abundance in samples above 25 cm depth. These deposits represent a series of fires occurring in the 20th century that began with the “Great Fire of 1914.” Development of the marsh for grazing purposes and celery culture made the marsh more susceptible to fire. Documented fires also affected the marsh in the late 1940s, early 1950s, 1957, 1971 and 1996.

Charcoal/pollen ratios in the core are highest at 110-115 cm depth (11.3 and 7.53) and 0-20 cm (0.59 to 6.9). Charcoal deposition rate (grains/gm/cm/yr) is also high in these intervals (1.3 x 106 to 2.8 x 106 and 3.6 x 103 to 2.0 x 105, respectively). Charcoal is only encountered sporadically at depth below 120 cm and indicates fires in Devonshire Marsh are principally related to human activity.

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-344397

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