INCREASING RISK OF WILDFIRE IN NEW ENGLAND: SEDIMENTARY PERSPECTIVES FROM PAST WARM INTERVALS

Wildfire plays a strong disturbance role in forest ecosystems and poses many societal risks as the wildland urban interface grows. Modern wildfires in New England are largely triggered by human activities. Holocene paleolimnology records indicate that wildfires in the region occurred frequently in the past, but the triggering circumstances are uncertain. Many studies attribute paleofires to native peoples because humans occupied the region throughout the Holocene. Few studies include paleoclimate evidence of pre- and post-fire conditions, however. We present initial evidence linking local wildfire occurrence in the Cone Pond, NH watershed to past climate characteristics, including changes in forest composition, and sedimentary evidence of seasonal drought and inundation.

Cone Pond (43.9035, -71.6045) is a 33.4 ha, 8-m-deep, naturally acidic (pH 4.5-4.8), headwater pond at 650 m elevation in an undeveloped landscape of central New Hampshire. Cored in 1977 by J. Ford, the sediment was sampled for loss-on-ignition, pollen, diatoms and C14 dates, but never split. Re-examination of the relict core in 2019 revealed abundant very fine laminations suggestive of chemical varves. In 2021, we collected surface cores from Cone Pond, completing Pb210, loss-on-ignition (LOI), pollen, magnetic susceptibility (MS), and charcoal analysis on CP2-2021. In 2022, we collected two 7-m-long, side-by-side Livingston cores and have since completed the following analyses on CPB-2023: XRF and MS scans, at 2 mm resolution, and LOI, charcoal, pollen and C14 dating, at 50 cm resolution. Higher resolution sample analyses and 10 C14 dates are pending.

Results so far provide a core bottom minimum date of 11,320 ±80 cal yr BP, from an organic-rich layer embedded within glacial silt. Correlation with the 1977 core indicate transition to organic-rich sediment occurred along with expansion of Picea (spruce) by 10,250 cal yr BP, with a fire adapted red/pitch pine-dominated forest by 9525 cal yrs BP. Data for the 3000-9000 year interval are pending but charcoal analyses of the last 3000 years show a peak in large charcoal (>250 μm) around 2200 cal yrs BP. This interval is associated with a peak in red/pitch pine and a sharp increase in sedimentary titanium, consistent with post-fire soil erosion and pollen production by fire-adapted vegetation.