Because each plant species has unique pollen grains or spores, by examining New Zealand’s wetland deposits researchers such as Janet Wilmshurst can tell what types of plants grew in a particular area at a particular time. The coincidence of a sudden, very marked and sustained decline in pollen from trees with a sudden increase in bracken spores (a plant which colonises open ground) indicates that forests have been destroyed through deliberate burning, and that bracken has occupied the bare ground.
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Photograph by Ian Raine
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