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In most parts of the world where people have colonized and modified their landscapes for several millennia or more, it is often difficult to discriminate anthropogenic burning from natural fire regimes that are linked to climate regimes. New Zealand provides a unique setting for identifying human influence on fire occurrence because it was settled recently ( c. AD 1280) at a time when climates are considered to be similar to today. Late-Holocene pollen and charcoal records from New Zealand provide striking evidence for initial Polynesian (Māori) arrival being strongly associated with widespread burning and loss of native forest. The duration of initial forest clearance and the spatial pattern of burning that led to this transformation are still poorly understood. We present high-resolution charcoal and pollen analyses of sediment cores from five lakes, located on the deforested eastern side of the Southern Alps. These records document the local fire history of the last 1000 years and the response of vegetation and watersheds to burning. Our results suggest that one to several high-severity fires occurred within a few decades of initial Māori arrival, and this ‘Initial Burning Period’ (IBP) resulted in the majority of forest loss and erosion. Changes in sedimentation rates, soil chemistry and magnetic susceptibility occurred simultaneously with the first fires at some sites, and marked the end of the IBP at others, suggesting substantial and rapid alteration of watershed vegetation, soil and biochemistry. Timing of the beginning of the IBP varied across sites but the duration of this period was brief (decades to a century). Our results suggest that Māori burning of native forests was deliberate and systematic. These forests had no previous history of fire and thus showed little resilience to the introduction of a new disturbance.