Floristic changes over 30 years in a Canterbury Plains kānuka forest remnant, and comparison with adjacent vegetation types

The Canterbury Plains have lost most of their pre-Polynesian indigenous vegetation, primarily forest and shrubland. One of the few remaining areas is the 2.3 ha Eyrewell Scientific Reserve which consists mostly of low kānuka (Kunzea ericoides) forest and a small area of grassland. We assessed the Reserve vegetation using a combination of plots and transect surveys at different times of the year between 2001–2003. For comparison with the Reserve vegetation we also assessed plots in an adjacent grazed kānuka remnant, adjacent cultivated pasture and Eyrewell Forest, a pine plantation. Our study of the Eyrewell Reserve in 2001–2003 found that since an assessment of the Reserve in 1972, 28 indigenous species were no longer present but 14 indigenous species and 48 adventive species were newly recorded. The dramatic invasion of the Reserve is illustrated by the fact that 60% of the 118 species recorded in 2003 were adventives compared to 34% in 1972. Despite this invasion and the loss of indigenous species, Reserve plots still have more than twice as many species as plots in the adjacent pine plantation. The Reserve also included several species of high conservation value such as the “Chronically Threatened” Leptinella serrulata, and the “At Risk” Aciphylla subflabellata, Coprosma intertexta and Pterostylis tristis. Plots in the Reserve grassland and adjacent pasture had the lowest percentage of indigenous species of all habitat types, with the pasture plots having no indigenous vascular plant species. In contrast the understorey of the old pine stands had the highest percentage of indigenous species of any of the habitats and in places was dominated by kānuka up to 4 m tall, indicating that these plantations also have conservation value. Eyrewell Reserve and the few other remaining kānuka remnants in the Canterbury Plains represent an important pool of indigenous species for conservation. Options for the future management of the Reserve are discussed.