Nassella trichotoma (Nees) Arechav.: seedling recruitment and survival in New Zealand

摘要

As part of a long-term project on the ecology of Nassella trichotoma (Nees) Arechav. in New Zealand grasslands, the effect of aspect and soil disturbance/vegetation cover on seedling recruitment and survival was investigated. At each of three field sites in grazed grassland in North Canterbury, plots were established with the following treatments: (a) with and without added seed of N. trichotoma (1600 seeds m~(-2)), (b) disturbed pasture (soil bared by chipping away existing vegetation) at the beginning of the experiment vs. undisturbed pasture, and (c) northern (sunny) vs. southern (shady) aspects. Recruitment and survival were measured at 12 and 24 months after sowing respectively. Irrespective of aspect or disturbance, there was little recruitment in plots without added seed (<4 seedlings m~(-2)), whereas the average recruitment was 204 seedlings ~(-2) when seed was added. This suggests that recruitment is seed-limited at the experimental sites. Soil disturbance promoted recruitment but had no effect on survival rates indicating that the soil disturbances associated with chipping may contribute to population growth in this weed. Recruitment was higher on southern than on northern aspects but there was no evidence of a difference in survival during the 2-year period of the study, suggesting that the rarity of N. trichotoma on southern aspects in North Canterbury may be due to delayed mortality.