Alpine phytomass and primary productivity in central Otago, New Zealand

Phytomass was measured and net potential productivity estimated for normal climatic conditions on the Otago rainshadow mountains. 7 tall snow tussock grasslands were compared with lower-statured cushion, herbfield and short grassland communities. The main grass spp. were Chionochloa macra, C. rigida and Poa colensoi. Total phytomass ranged from 5 to 9 kg/m² (22 000-40 000 kcal/m²) in tall tussock and from 2 to 4 kg/m² (8100-16 500 kcal/m²) in cushion, herbfield or short grassland vegetation. Root:shoot ratios of <1, in all communities, probably reflected the oceanic nature of the climate. Total annual potential net production ranged from 0.7 to 1.0 kg/m² (3200-4600 kcal/m²) in tall tussock, and was 1.0 kg/m² (4200 kcal/m²) in an induced mid-alt. Poa colensoi turf grassland. Growing season efficiency ratings (0.5-1.2%) tended to increase with alt., suggesting an adaptation to the short and climatically erratic summers. The 150- to 200-day growing seasons were considerab!