Growth, biomass, and net productivity of tall-tussock (Chionochloa) grasslands, Canterbury, New Zealand

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Abstract
Stands dominated by Chionochloa rigida and C. macra were studied at 884 and 1 257 m, on infertile soils related to high country yellow-brown earths. Solar radiation, wind, precipitation, temperature (air and three soil depths) at the sites are concordant with the regional pattern of long-term stations. Climatic conditions at the Macra Site are more severe than at the Rigida Site, but both fall within the range of the coniferous forest biome (mean annual temperature 6–7°c, total precipitation 1 000 m). Total above-ground tall-tussock biomass from destructive sampling during summer is 3 800 g/m2 for C. rigida and 1 600g/m2 for C. macra. Live biomass is 770 g/m2 and 360 g/m2 respectively. Indirect measurements using a modified height-frequency method were within 5% of these results. Root biomass (live and dead) is 3 100 g/m2 at the Rigida Site and 2 200 g/m2 at the Macra Site. Roots are denser beneath tussock than between tussocks, where 68% of roots at the Rigida Site (50 cm profile), and 50% of those at the Macra Site (45 cm profile) are within the top 10 cm. Between-plant differences in ratios of live and dead material, shoot densities per tussock, and shoot weights are discusscd in relation to inferred age differences within C. macra. Leaf elongation rates peak in mid-summer in contrast to the summer-plateaus of previous tall-tussock studies. Seasonal variation in leaf number and shoot composition are discussed in relation to growth patterns. Shoot net productivity (leaves only) is 518 g/m2 for C. rigida and 330 g/m2 for C. macra, over a 7.5-month “growing season”. Leaf die-back rates peak during autumn on live leaves, but outer-most leaves may completely die at any time of the year. Leaf number per shoot reaches a maximum in mid-summer. Sheaths continue to increase in weight as their blades are dying. 47% of C. rigida annual dead-leaf production (total 518 g/m2) and 27% of C. macra (total 294 g/m2) occurs in the summer, but rates peak in autumn at 2.7 g/m2/day and 2.5 g/m2/day respectively. All figures include ash.

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