Factors influencing abundance of invasive hawkweeds, Hieracium species, in tall tussock grasslands in the Canterbury high country

Abstract

Hawkweed (Hieracium species) invasion in the tussock grasslands of South Island, New Zealand, has been well documented. Distribution of these species ranges from montane to alpine grasslands, from Hawkes Bay to Southland. This study quantifies the distribution of three Hieracium species in a high country tall (snow) tussock grassland along the Upper Cass River. Hieracium pilosella and Hieracium praealtum are widespread throughout the study site, whereas Hieracium lepidulum is rare. Major factors influencing the abundance of H. pilosella and H. praealtum are altitude and dense vegetation cover such as tall tussocks, large herbs and sub-shrubs. Both H. pilosella and H. praealtum are present at high altitude,>1800 m above sea level. Differences in the invasion stages of Hieracium species are evident. Mean abundance of H. pilosella ranged from 0.5% cover at altitudes > 1800 m above sea level, to 60% cover at altitudes < 1200 m above sea level. Hieracium praealtum averaged 0.5% cover at all altitudes.