Determination of the direct causal factors controlling wildfires is key to understanding wildfire-vegetation-climate dynamics in a changing climate and for developing sustainable management strategies for biodiversity conservation and maintenance of long-term forest productivity. In this study, we sought to understand how the fire frequency of a large mixedwood forest in the central boreal shield varies as a result of temporal and spatial factors. We reconstructed the fire history of an 11,600-km2 area located in the northwestern boreal forest of Ontario, using archival data of large fires occurring since 1921 and dendrochronological dating for fires prior to 1921. The fire cycle decreased from 295 years for the period of 1820-1920 to approximately 100 years for the period of 1921-2008. Spatially, fire frequency increased with latitude, attributable to higher human activities that have increased fragmentation and fire suppression in the southern portion of the study area. Fire frequency also increased with distance to waterbodies, and was higher on Podzols that were strongly correlated with moderate drainage and coniferous vegetation. The temporal increase of fire frequency in the central region, unlike western and eastern boreal forests where fire frequency has decreased, may be a result of increased warm and dry conditions associated with climate change in central North America, suggesting that the response of wildfire to global climate change may be regionally individualistic. The significant spatial factors we found in this study are in agreement with other wildfire studies, indicating the commonality of the influences by physiographic features and human activities on regional fire regimes across the boreal forest. Overall, wildfire in the central boreal shield is more frequent than that in the wetter eastern boreal region and less frequent than that in the drier western boreal region, confirming a climatic top-down control on the fire activities of the entire North American boreal forest. © 2010 Springer Science+Business Media, LLC. Abstract reproduced by permission.