Fighting Hieracium Weed in the Mackenzie

October 2011

Pest weeds and grassland recovery work at a scientific reserve in the Mackenzie Basin

The 1000ha Lake Tekapo Scientific Reserve is one of several in the Mackenzie Basin set aside in government ownership as regionally significant natural areas or landscapes. DoC Twizel office looks after the reserve, controlling weeds and pests and providing access along the Lake Tekapo Walkway. DoC staff members, Landcare Research and other scientists are observing the regeneration of tussock grasslands, over a long time scale, following depletion of vegetation by livestock grazing and the invasion of rabbits and hieracium weeds.

The Tekapo Accommodation Reserve was allocated to the Department of Conservation (DoC) in 1987. Originally set aside to provide grazing for an accommodation hotel at Tekapo in the 1860s, it was reclassified as a scientific reserve in 1996 to recognise the reserve’s conservation values and the opportunities it provided for scientific research and education. It comprises 1058 ha of fescue tussock grassland and and ephemeral wetlands on moraines and glacial outwash immediately south of Lake Tekapo in the Mackenzie Basin.

According to former AgResearch Invermay researcher Peter Espie, land in the reserve lay on the boundary between the original Sawdon and Tekapo Stations, and was probably burnt and grazed from about 1865. The back slope of the moraine was cultivated around the turn of the century, and probably sown with improved grasses to provide hay. Like many areas immediately after the first world war, the reserve was over-run with rabbits, and was probably not, or only very lightly, grazed by stock in the 1920s. When T.D. Burnett acquired the area in 1927, he then leased it to Sawdon Station for grazing.

Losses from swamp fever saw the moraines fenced off from the outwash plain.

Merino ewes were run on the moraine in autumn and during winter and then on the outwash during summer until sold at the February Tekapo sale. This pattern of pastoral use continued until 1991, when DoC cancelled stock grazing.

The reserve was set aside during a period of great concern for the ecological health of the Mackenzie, which was under threat from rabbits and the invasive weed, hieracium. Essentially, the reserve was to illustrate that regeneration of natural flora and fauna would occur after retirement from grazing.

However, because of the risks posed by rabbits and hieracium, that was by no means a foregone conclusion. Rabbits were poisoned and are now shot on a regular basis, and hieracium bio-controls have been released all around the Mackenzie. After 20 years of retirement, the reserve contains lessons for farmers, ecologists, conservationists and, more recently, people who propose more intensive farming development under irrigation for parts of the Mackenzie.

Extract from Landcare Research website :

In January 2011, Kate Ladley, Dean Clarke, Alex Ghaemaghamy and Susan Walker (all Landcare Research dryland ecologists) teamed up with DOC colleagues from the Twizel Area Office in a new study at Tekapo Scientific Reserve to ask whether (and to what extent) degraded grassland communities can recover under conservation management.

Tekapo Scientific Reserve is a crucial site for understanding biodiversity resilience in the Basin. At ~1000 ha it’s the only sizeable place where stock have been absent and rabbits and wilding pines controlled to low levels for nearly 20 years. When it was destocked in 1992, bare ground and mouse-ear hawkweed (hieracium) dominated and tussocks were virtually absent.

In 1993, 12 permanent grassland plots were established, sampled, and photographed in the new Reserve, forming a monitoring baseline against which changes could be compared.

Our tasks in January 2011 were twofold: to resample the original permanent plots, and to augment the original monitoring design by installing new randomly-placed plots and using supplementary sampling methods at all plots. The project will allow us to document vegetation change over 18 years, describe recovering vegetation communities and native plant species on the different landforms, and compare the utility and biases of different non-forest monitoring methods. Importantly, it also lays a stronger foundation for assessing future changes.

Spurred along by a nippy (summer!) easterly, a field team of six spent a week laying out 20 x 20 m plots (new and old) and collecting data with four different sampling methods. Three of the sampling methods are new: they reduce potential misinterpretation of the data, and provide greater understanding of interesting changes such as increases in short tussocks and trends in community composition and richness. The augmented plot layout (based on coordinates generated in Landcare Research’s ArcSampling tool) better represents geographic space and vegetation variation across the reserve, adding statistical power and reducing bias.

Susan Walker says “It was busy but rewarding work. The indigenous plant communities of the reserve are evidently bouncing back: the resurgence of tussocks and other palatable native species has been astonishing, and looks set to continue. And it’s just a neat place! Dozens of tiny cryptic native plants inhabit a diverse micro-world, there are several rare and uncommon species, and the landform variation is fascinating (lumpy moraines with ephemeral wetlands and erratic boulders, a moraine fan, thirsty river terraces and escarpments, and a vast aeolian duneland over outwash gravels). It’s a pleasure to be involved with this site, and to set it up with a stronger monitoring system for the future. ”

At this stage Susan Walker et al have not published the results of their survey work in January.

Rob Young, DoC Twizel, will speak generally about the ongoing conservation work in the reserve, including rabbit control. Before the big poisoning in 1991 rabbit counts of 200-plus per kilometer were taken in the reserve. Patch poisoning with pindone and night shooting kept the numbers down until the release of Rabbit Calicivirus in 1997. No major poison or bait drops have been done since then. Currently the control measure is regular night shooting, and the rabbit counts are now less than one rabbit per kilometer.

The reserve is rabbit fenced and DoC has to maintain that fence.