Water and nutrient input:output budgets: effects of plant cover at seven sites in upland snow tussock grasslands of Eastern and Central Otago, New Zealand

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Abstract
Input:output budgets of water and macronutrients over two years are reported for three cover types (unmodified snow tussock grassland; induced short (c. 10 cm) blue tussock grassland; bare soil) in replicated non-weighing lysimeters from seven upland sites, four on the Lammerlaw Range (487 m–976 m), Waipori Ecological District, Eastern Otago and three on the Rock and Pillar Range (1000 m – 1340 m), Rock and Pillar Ecological District, Central Otago. Values for alpine Celmisia viscosa herbfield and for a ryegrass — white clover pasture are included for the highest and lowest sites, respectively. Snow tussock grassland produced the greatest water yield at all six sites above 700 m. Here mean annual precipitation exceeded potential evapotranspiration (PE). Annual yields from snow tussock grassland ranged from 80% of the measured 1372 mm of precipitation on the southern Lammerlaw Range to 12% of 510 mm at the lowest site near the northern end of this Range. Yields from blue tussock turf, bare soil and Celmisia herbfield were generally similar within sites but ranged between sites from 16% to 62% of measured annual site precipitation. Water yield from the pasture sward (one site) was negligible (-1), followed by snow tussock grassland (23.1 mm), blue tussock grassland (17.6 mm), bare soil (17.0 mm) and Celmisia herbfield (9.2 mm). PE values derived from porous pots (7 mm wk-1) were about half the field values. The increased water yield associated with snow tussock grassland is only partly related to its relatively low AE values. It also reflects interception gains from wind-driven fog (and rain) by the tall caespitose habit and linear leaves of the dominant tussocks. Such gains may reach c. 120 mm annually at the most fog-prone site on the southern Lammerlaw Range. Here, water yield relative to the rain gauge catch was greater over the snow-free six months (86%), when fog is most common, than for the full year (80%). Input-output budgets for nine nutrients revealed only minor annual and seasonal variations in inputs but the values for the Lammerlaw Range were significantly higher than those for the Rock and Pillar Range, because it is closer to the coast. Outputs were greater than inputs (concentration ratios ranged from 3.0 to 4.7), but generally in the same proportions, indicating that solum effects are outweighed by concentration increases associated with evapotranspiration. The relevant literature and implications for land management are discussed.