Late Holocene vegetation and fire history at the southern boreal forest margin in Alberta, Canada

A transect of three shallow ponds across the Aspen Parkland/Boreal Forest transition in Elk Island National Park, Alberta, Canada, shows changes in late Holocene vegetation and disturbance dynamics, and consequent carbon storage, in response to climate change and to recent anthropogenesis. Pollen and charcoal analyses reveal unexpected changes in fire regime. Although there is the expected decline in fire activity during the historic period, presumed due to agricultural clearance around the park, there is also a prehistoric fluctuation in fire regime at one of the sites. Pollen evidence suggests that the fluctuations in fire regime may be due to changes in hydrology. Declining groundwater levels during the Medieval Warm Period allowed the replacement of substantial areas of shrub birch (Betula glandulosa) with the less fire-prone aspen (Populus tremuloides) causing a decline in fire frequency and/or severity, while increasing carbon storage on the landscape. This is counter to the intuitive increase in fire activity with warmer and drier climate. Canadian national parks are currently managed under a ‘natural processes and conditions’ paradigm; the changes in conditions and consequent changes in processes evident due to the relatively minor climatic fluctuations of the Little Ice Age and Medieval Warm Period shown here suggest a need to revisit this paradigm in consideration of future anthropogenic climate change.