Long-term fire and vegetation interactions at local and sub-regional scales in the central boreal forest
Fire history reconstructions based on charcoal preserved in lake sediments have been used to improve our understanding of Holocene fire regimes in many boreal forest regions. Sedimentary charcoal, plant macroremains and pollen from six lakes in north-western Ontario, Canada, were analysed in order to investigate fire frequency and vegetation dynamics at the local and sub-regional scale in the central boreal forest. Lakes are subdivided into eastern and western groupings based on local proximity among sites and shared local physical site characteristics. These records were used to examine the controls over the long-term fire regime and vegetative dynamics associated with fire return intervals (FRIs). Vegetation reconstructions at high temporal resolution, together with a fire event reconstruction inferred from sedimentary charcoal, were analyzed by Superposed Epoch Analysis (SEA) to model local vegetation behaviour before, during and after fire events. Regional vegetation-population dynamics were analysed by the use of a standardised pollen influx combined with Principal Component Analysis (PCA).
This study provides insight into the millennial scale fire-climate-vegetation dynamics at the local and sub-regional scale in central boreal forests of North America. Among groups, sites inthe eastern and western grouping possess similar fire frequencies throughout the Holocene, between groups; the eastern sites have a higher average fire frequency. Fire frequency among the western sites are strongly influenced by climate, while eastern sites exhibit local variation in fire occurrence indicating local non-climatic factors contribute to the sub-regional fire regime. Locally, Pinus banksiana is present in large quantities prior to fire events when FRIs are short in both the east and west; the species primary abundance is found pre-fire when average FRI is < 180 years. Increased occurrence of fire led to a decline in the pre-fire local abundance of Betula papyrifera in the west. Preliminary results in western sites, PCA scores show gradual trends, suggesting a regional lack of response to fire frequency change. In eastern sites where fire frequency was stable throughout the Holocene there too were gradual trends in PCA scores. Results indicate that at the regional scale the central boreal forests are resilient to changes in fire frequency.