One hundred years of vegetation change at Cass, eastern South Island high country

Fire, pastoral farming and exotic species have been major drivers of vegetation change in the eastern South Island high country since human arrival. More recently, fire frequency and grazing intensity have declined allowing regeneration of previously suppressed woody elements in some areas, such as our 1775 ha Cass study site. We collected vegetation and abiotic data from 117 Recce plots (10 × 10 m) using an objective grid-based network to classify the vegetation, determine factors influencing vegetation pattern, discuss long-term vegetation changes and assess the role of exotic species. Hierarchical cluster analysis and ordination on compositional data revealed seven broad vegetation types: grassland, mixed shrubland, mānuka shrubland, mountain beech forest, gorse shrubland, wetlands and subalpine vegetation. Within four of these types (mixed shrubland, grassland, subalpine, wetlands) distinct subtypes were also identified. There was evidence for compositional structuring based on altitude and slope. Two vegetation types were characterised by exotic species (gorse shrubland, grassland), with exotic species more common at lower elevations and on gentle slopes. While short tussock grassland dominated the Cass landscape in the early twentieth century, having been induced by burning and grazing, it only dominates 8% of the landscape today. Native woody vegetation (predominantly shrubland) is now the dominant land cover at Cass. As long as fire is excluded, grazing is limited (but not necessarily eliminated) and exotic woody species are controlled, is it likely that these transitional shrublands will be replaced by mountain beech forest in the longer-term. Similar patterns of recovery of native woody elements are likely to occur more widely in similar high country environments in the absence of fire and with careful management of grazing and exotic woody plants.