At the time of Māori settlement, ca. 750 years ago, New Zealand's ecosystems experienced catastrophic change, including the introduction of fire to ignition-limited ecosystems and the resulting widespread loss of forest. While high-resolution sediment-charcoal analyses suggest this forest loss was rapid, Māori populations were small and transient during the Initial Burning Period and there is evidence for widespread fire activity in places where there is little archaeological evidence of human presence. These observations beg the question ‘how did small populations manage to transform large areas so rapidly?’ Using a simulation model, we demonstrate how the relationship between time since fire and flammability in New Zealand's forests drives positive feedbacks that allow for rapid and extensive deforestation. Under ignition scenarios mirroring prehuman conditions, the model did not produce significant deforestation – thus, it is extremely unlikely that deforestation could have occurred without human-initiated burning. Scenarios where ignition was spatio-temporally random also failed to result in deforestation. Rapid and widespread forest loss occurred in scenarios incorporating spatio-temporally savvy selection of ignition locations. Targeting ignitions in flammable vegetation was more important than targeting ignitions in years with favourable climatic conditions. However, targeting in space and time concurrently, such that flammable vegetation was ignited during favourable climatic years was the most efficient strategy of those simulated. Following the Initial Burning Period decadal ignitions would have been sufficient to maintain a deforested shrubland/grassland landscape. New Zealand's Initial Burning Period is one of many that occurred across eastern Polynesia following human settlement, and these events have left long-term legacy effects that remain evident in contemporary landscapes. Improving understanding of how humans shaped environments in New Zealand in the past has implications for eastern Polynesia as a whole.