Fire History Reconstruction in the Black Oak (Quercus velutina) Savanna of High Park, Toronto

We employed tree-ring analysis to reconstruct the fire history of High Park, Toronto, Canada, in one of the largest remnants of black oak (Quercus velutina) savanna in Ontario. This heavily urbanized area has a long history of fire suppression, which has degraded the native savanna. Efforts to reintroduce fire would benefit from a fire history record. Ring width patterns were quantified for 38 black oak chronologies on 14 cross-sections and 10 cores using dendrochronology software that employs scanned (digital) ring sequences. Scar and sealing patterns and rapid growth responses following scarring were dated to indicate the timing of fire events. These dates were compared with the timing of regeneration pulses and the establishment of multistemmed individuals that would have sprouted in response to fire disturbance. Our records suggest that most of the mature black oak stems established synchronously, around 1865, following an apparently extensive fire event or set of events. We have evidence of four other fires in the century that followed. Dendrochronology in black oak savanna presents challenges due to this tree species' thick bark, and the low intensity savanna fires that do not breach all individuals in a stand. Further, the present black oak population has succumbed to disease and old age, leading to decay of the central stem and the loss of the oldest rings that were more likely to be scarred as they formed during the tree's youth. This is likely to be a limitation in other savanna communities in long-settled regions of North America. We suggest inclusion of corroborative evidence, such as that employed in the present study, including the use of multistemmed individuals as indicators of stem recruitment following fire, and demographic data for the population.