A Holocene-scale analysis of fire regime using sedimentary charcoal from Little Black Lake, eastern Ontario, Canada

Abstract

As part of Parks Canada’s management initiatives, St. Lawrence Islands National Park (SLINP) funded this study to learn more about the natural local fire regime, learn about the risks associated with fire in a changing climate scenario, and to aid in protection efforts of the fire-dependent species Pinus rigida (pitch pine), which is listed provincially as a species at risk. The study site selected was Little Black Lake (44º 32'45.20" N, 76 º 03'12.06” W), which is ideal because of its small size and isolated watershed. A 4.5 m Livingston-piston core and a 0.5 m Glew gravity core were extracted from the lake basin. Charcoal macrofossils >125 µm were quantified at 0.5 cm intervals to produce a high-resolution (14 years) fire record. A chronology was created for each of the two cores together using a combination of 13 14C dates and 20 210Pb dates to complete a record spanning from 2008 to >11000 Cal yrs BP. In general, the fire regime appears to be non-stationary with overall low CHAR (charcoal particles per cm2 of sediment per year) throughout the Holocene. The mean fire return interval for the entire record was on the century scale, at 244 years. The early- and mid-Holocene show low CHAR and few peaks during a period dominated by spruce and pine. Contrastingly, the late Holocene shows an increase in CHAR and peaks during hardwood dominance, which may be due to a change in fuel, as suggested by charcoal morphotypes. A detailed look at the Late Holocene through an analysis of the Glew gravity core, shows a shorter mean fire interval. Comparisons of the Little Black Lake fire record with other vegetation and charcoal records from this region indicate interactions between climate and changing fuel sources may be explanations for the non-stationarity of the fire regime. Management steps for St. Lawrence Islands National Park could include continuing small, isolated and infrequent burns and continued monitoring of local Pitch Pine populations provided spatial and temporal heterogeneity are taken into account.