Effect of exclosure on soils, biomass, plant nutrients, and vegetation, onunfertilised steeplands, Upper Waitaki District, South Island, New Zealand

We sampled soils and vegetation within and outside two sheep and rabbit exc losures, fenced in 1979, on steep sunny and shady slopes at 770 m altitude on seasonally-dry pastoral steeplands. The vegetation of sunny aspects was characterised by higher floristic diversity, annual species, and low plant cover. Here the exotic grass Anthoxanthum odoratum dominated on grazed trea tments, and the exotic forb Hieracium pilosella on ungrazed. Shady aspects supported fewer, and almost entirely perennial, species. Here Hieracium pil osella dominated grazed treatments, but co-dominated with the exotic forb H . praealtum and the native grass Festuca novae-zelandiae on ungrazed treatm ents. There was 43% more biomass in exclosures (P < 0.01). Most of the biomass di fference (4285 kg/ha) was from greater root mass (2400 kg/ha). 1385 kg/ha o f the difference was from herbage and the remainder (500 kg/ha) from litter . Exclosures had 50 to 100% more Ca, Mg, K and P in the biomass (P < 0.05), but the effect on soils was limited to significantly higher concentrations of total N (P < 0.05) and exchangeable Mg (P < 0.01) in 0-7.5 cm soils. We conclude that stopping grazing for 16 years on seasonally-dry steeplands results in greater plant cover, approximately double the biomass of standi ng vegetation, greater biomass in roots, and more biomass nutrients relativ e to grazed areas. However, it does not favour native species and has littl e effect on soil nutrients or soil carbon. Stopping grazing alone therefore cannot be regarded as a comprehensive short- or medium-term vegetation or soil rehabilitation option.