The shifting floristic complexion of Molesworth

Drought-resistant woody communities were once widespread in the intermontane basins and slopes of Molesworth Recreation Reserve, northeastern South Island. These forests, woodlands, and shrublands had established by 6000 years BP, and were largely converted to tussock grassland by fire before 1800 AD. Sheep and rabbit herbivory, and regular burning had altered the vegetation by 1940. From the 1940s, beef cattle grazing was adopted on Molesworth along with repeated aerial over-sowing of exotic pasture grasses and suppression of fires. A series of permanent plots were subjectively located (n = 22), randomly located (n = 80) and paired along fence lines (n = 66) between 1989 and 2008. Plots were re-measured in 2016 to determine vegetation change on Molesworth. We used these data to investigate the effects of cattle grazing and aerial oversowing of exotic pasture grasses on changes in vegetation. Native species richness, cover, and biomass increased between 1989 and 2016. Native herbaceous species cover and biomass increased more at higher elevation and at sites fenced to exclude cattle. Woody biomass, predominantly low-statured native species, increased most on oversown, low elevation slopes in the northern part of Molesworth. The number of exotic species in plots increased at a similar rate to native species, but the biomass of exotic herbaceous species increased at more than twice the rate of native herbaceous species. Data from plots measured in 1952 (n = 24), 1960 (n = 10), 1987 (n = 591), and 2012 (n = 9) were used to show that cover of native species has been increasing for the past six decades, as have woody species, both native and exotic. Restoration of native plant communities on Molesworth requires control of grazing and browsing pressures, ongoing fire suppression and active management of invasive plants.