Late Holocene drought variability and wildfire occurrence in Maine

Background/Question/Methods

In portions of western North America there is a relatively well-known relationship between wildfire and climate, where climatic variability exerts a strong control on biomass burning at multiple temporal scales. In humid regions, such as the Northeast, few large wildfires have occurred during the past century, thus much less is known about fire-climate relationships. Paleoecological studies from the Northeast and upper Midwest suggest that wildfire frequencies can be strongly controlled by both vegetation-type and climate at millennial timescales. However, few direct comparisons of independent paleoclimatic records and fire histories have been made, particularly at multidecadal-to-centennial scales. In this study, we developed coupled records of hydroclimate and fire history using the sediments from three moisture sensitive peat bogs in Maine. We used testate amoebae and measures of peat humification to infer past moisture variability, and quantified charcoal fragments (15-300 µm) to infer the timing of past wildfire events. We used our data to explore drought-fire relationships in this region for the past 2800 years.

Results/Conclusions

Hydroclimate records from the three sites were coherent, indicating that they record a regional moisture signal at multidecadal to centennial scales. Charcoal records show that nearly all local wildfires at the three sites occurred synchronously with periods of prolonged regional drought, with the most striking exception being fires that occurred at the time of European land clearance. At two of the three sites the probability of wildfire occurrence during drought periods was >30%, which was over 3-times greater than during average hydroclimatic conditions. No fires were recorded during pluvial periods. Our records show that prolonged drought conditions have been a recurrent feature of Maine climate prior to the 20^th century, and demonstrate a clear linkage between fire and drought variability in this humid region. Although drought and fire have generally not been considered primary drivers of ecological change in forests of the Northeast, our data indicate the potential importance of drought and fire in the coming century.