The current vegetation pattern of Barrett Bush is the result of complex landscape changes of both recent and historic times. The most recent natural landscape changes occurred as the Waikato River meandered across the region, changing course over many years and depositing the alluvial plain that Barrett Bush grows on. More recent landscape changes have been the result of human activity as vegetation clearance and agricultural development has occurred throughout the district. Fortunately, Barrett Bush was set aside and the reserve now provides insight into original vegetation patterns as well as a refuge for biota characteristic of forests dominated by kahikatea. Barrett Bush sits a shallow depression of an alluvial plain with a podocarp vegetation composition that is classed as a kahikatea semi-swamp forest (Clarkson et al. 2007). Clarkson et al. (2007) describe the typical natural vegetation of kahikatea semi-swamp forest: “Semi-swamp forest dominated by kahikatea grew on the poorly drained shallow depressions. Several other species were present in varying amounts, including rimu, matai, pukatea, swamp maire, tawa, pokaka, and occasional cabbage tree. Prominent in the understorey were silver fern, mapou, hangehange, Coprosma areolata, and turepo, and sedges including Hymenophyllum demissum, hen and chicken fern, Astelia fragrans, A. grandis, and Microlaena avenacea.”