Plants release pollen or spores, which are blown by the wind and settle onto the surrounding land, lakes and peat bogs. By taking a core sample from a lake bed or peat swamp and looking at changes in the types of pollen and spores that have settled in different sediment layers, scientists such as Janet Wilmshurst and Matt McGlone can analyse past changes to New Zealand’s vegetation patterns. The pattern of pollen and spores from Travis Swamp and elsewhere shows a marked change from forest pollen to raupō (reed) pollen and bracken spores in the late 1200s and early 1300s. Such a dramatic change in the vegetation pattern is an indication that forests were deliberately burned by the first human settlers. They did this to make way for kūmara (sweet potato) cultivation and to encourage bracken fern growth (the underground stems were a source of food), and other reasons.