Distribution of three Hieracium species in the Mt Possession area, mid Canterbury, New Zealand

The abundance of three Hieracium species was examined in the Mt Possession area in relation to soil and other site variables. For H. pilosella cover, total soil P and elevation were the most significant combined predictors, but together explained only 30% of the variation. H. pilosella had the highest cover at relatively high P levels and at low elevation. The presence of H. praealtum was predicted by moisture index, while that of H. caespitosum was predicted by tussock height and C:N ratio in the soil. However, none of the measured site variables significantly predicted the cover of H. praealtum and H. caespitosum. The present cover distributions of H. pilosella and H. praealtum were compared with a 1960s survey in the area. The distribution of H. pilosella cover frequency had changed from being skewed with the species absent or in low cover in 1960s, to becoming common and the cover frequency for H. pilosella showing a normal distribution with the highest frequency at cover class 2 (5-25% cover). H. praealtum was absent or in relatively low cover in both surveys. The P response curve for H. pilosella contradicts other studies, and shows the need for specificity about what environment and vegetation are studied. The differences in spatial and temporal variation among the three Hieracium species also emphasise the need to consider therm separately when discussing their ecology and management.