Part 1 - Land Information New Zealand

RELEASED UNDER THE OFFICIAL INFORMATION ACT
• To maximise water yield it is necessary to maintain tall, unmodified tussock vegetation over
the headwater catchments. This is best achieved by completely destocking these areas, preventing
fires of any kind and controlling wilding pine tree growth.
Mark and Rowley (1969) demonstrated that undisturbed snow tussocks produced a greater water
yield than either a sward of blue tussock or snow tussocks which have been recently defoliated by
clipping or burning.
Duncan and Thomas (2004) in their study of the hydrological effects of burning tall tussock
grasslands on the Lammerlaw Range showed that for the summer period, modification of tall
tussock grassland did reduce water yield. Measured decreases in catchment runoff were greatest
in the first two years following burning, as tussock tillers rapidly grow from surviving tussock
stumps and deplete soil moisture. Duncan and Thomas concluded that “burning tall tussock
grassland reduces water yield in the short term (2-3 years). It can be implied from this and other
studies that if burning and grazing persist, then so will reductions in water yield.
5. Water Supply and Retention
Fitzharris (1979) notes that the accumulation of snow into drifts is largely controlled by microrelief
in the landscape. He also makes the observation that the presence of snow tussocks assists
in the accumulation of drifts or a more widespread snow pack. The annual snowmelt helps to
recharge the shallow regolith storage and sustains base flow over the summer. With less cover or
bare ground, freshly fallen snow tends to be blown away, by the strong winds which sweep across
the uplands, leaving only the frozen bare soil or ice coated rocks (Waugh 2005).
Fahey and Jackson, 1991(a) note that bogs are important water-holding areas for the headwaters of
many streams helping reduce flood peaks and sustain flows. They also state that “Evaporation
from tussock grasslands has important implications for water-resource management. The strong
physiological control of transpiration by tall tussock produces low rates of water use in summer
and contributes to the well sustained stream flow”.
Duncan and Thomas (2004) found depleted tussock catchments yield lower water flows and Fahey
and Jackson (1991b) attribute this in part to the higher transpiration rates from exotic pasture
species.
6. Erosion control and sediment retention
Snow tussock catchments monitored for sediment yield elsewhere in Otago have been shown to
have very low sediment yields by New Zealand standards (Waugh 2005).
7. Nutrient cycling
Monitoring elsewhere in Otago has shown that tussock covered catchments yield very good water
quality (ORC 1999).
ORC records taken in 1999 at Stonehenge on the Lammerlaw Range reveal high water quality
characterised by:
• Cool water temperatures
• High levels of dissolved oxygen
• Approximately neutral pH values
• Low conductivities
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