Changes in the Structure of Tall Tussock Grasslands and Infestation by Species of Hieracium in the Mackenzie Country, New Zealand

A plant sociological survey of tall-tussock grasslands in the Mackenzie country was repeated after an interval of 26-28 years. Changes in physiognomy of the grasslands which have been inferred from earlier studies have been found to be continuing on many sites. A noteworthy feature of most sites has been a reduction in number of indigenous species found. An increase in abundance of Hieracium pilosella or H. praealtum has occurred at most sites. About 140 species and 9 variables from 53 sites were interrelated in a direct unimodal ordination (canonical correspondence analysis). Ordination results of the 1960s and the 1989 data were compared and interpreted with respect to spread of Hieracium pilosella and H. praealtum. The dynamics of Hieracium infestation was studied within changing community structure. A distinct trend is demonstrated of increasing infestation with increasing grassland degradation.