We studied vegetation change on 142 permanently marked transects spread throughout tussock grasslands of Otago and Canterbury, in areas subject to both pastoral and conservation management. The transects
were established between 1982 and 1986 and re-measured between 1993 and 1999, providing a record of vegetation
change at each site over an interval varying from 10 to 15 years. Each transect consisted of 50 quadrats, each
0.25m², in which the presence of all vascular plant species had been recorded. For each transect, we calculated the
change between measurements in the mean number of species recorded per quadrat, and the change in the total
number of species recorded per transect. Averaged across all transects, there was a significant decline in species
richness between measurements at both the quadrat and transect scales. Small herbs (those ≤ 2 cm tall, excluding
Hieracium species) showed the greatest decline. On average, more than one quarter of the small herb species
present in a quadrat at the first measurement had disappeared within 10 years. Larger herbs, ferns, rushes, sedges
and grasses (excluding Chionochloa species) also declined significantly in species richness, reflecting declines in
the abundance of species in these groups. Woody species richness remained constant, while species in the genera
Chionochloa and Hieracium increased significantly in mean quadrat species richness, reflecting increases in the
abundance of these species along transects. The rate of decline in mean quadrat species richness was unrelated to,
changes in the abundance of either Chionochloa or Hieracium species, or to an overall increase in total vegetation
cover on transects. The rate of decline in species richness was also unrelated to the level of grazing or burning
between measurements. However, the rate of decline in species richness was greater at lower elevation, on schist
rock and on yellow-brown and yellow-grey soils. Our results suggest that a major compositional change is occurring in these' grasslands at a rate that is independent of local variation in management and independent of the widespread invasion of these grasslands by Hieracium species.[Show full abstract]
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