Management of frost flat communities under threat from mouse-ear hawkweed invasion

Formerly extensive on the Volcanic Plateau, frost flat heathland dominated by monoao (Dracophyllum subulatum ) is now reduced to fragments. It is threatened by mouse-ear hawkweed (Hieracium pilosella) at the only major site where it is likely to survive indefinitely (Rangitaiki Conservation Area). In the past, fire has perpetuated monoao on frost flats, but in future it may accelerate the spread of hawkweed. This project aims to find ways of perpetuating monoao and minimising hawkweed spread, and of maintaining hawkweedfree samples of frost flat heathland. A randomised block trial was established at Rangitaiki C.A. in 1993 in 90-year-old monoao shrubland (burning, cutting, and control treatments) and in 30-year-old lichenfield (burning, herbicide, and control treatments). Two herbicides, 'Trimec' and 'Versatil', were tested. Vegetative cover was monitored by point intercept method before treatment and 20 months after treatment, and analysed by repeated measures ANOVA. In the shrubland, bare soil increased somewhat (p<0.01) after both burn treatments. Monoao decreased greatly (p<0.01) after all treatments. Woolly moss increased greatly (p<0.01) after all treatments. In the lichenfield, monoao decreased greatly in both burn treatments (p<0.01). Silver tussock increased somewhat (p<0.01) in the 'Versatil' herbicide treatment. Hawkweed increased substantially (p<0.05) after both burn treatments. No other changes in species cover were significant. Burning and cutting of mature frost flat heathland both largely eliminate existing monoao populations. Burning monoao communities with hawkweed already present leads to a substantial immediate increase in hawkweed abundance. Neither 'Trimec' nor 'Versatil' provide effective chemical control of it. Cutting mature frost flat heathland is not a means of reinvigorating monoao. Further experimental burns in mature heathland at a range of scales and involving a variety of fire intensities are necessary before prescriptions for operational burning can be formulated.