Gap size and regeneration in a New Zealand dairy pasture

Seedling emergence of three weeds ( Carduus nutans, Cirsium vulgare and Rumex obtusifolius ) and three clovers ( Trifolium repens, T. subterraneum and T. pratense ) was monitored in gaps of different sizes (0, 2, 6 and 10 cm diameter, plus a 3 m 2 bare plot), which were created in a Loliumperenne/T. repens pasture. Clover emergence was greatest in the bare plots, in contrast with the weeds, whose emergence peaked in small or intermediate‐sized gaps. Relationships between weed emergence and gap size in glasshouse swards were poorly denned. As a result of trampling by cattle, seedling mortality occurred most rapidly for all species in the bare plots. Very few weeds survived in the other gaps, where there was no detectable effect of gap size upon survivorship. Naturally occurring gaps were most abundant during summer, but their size frequency distributions varied little between spring and autumn. The sizes of almost 95% of the natural gaps were within the range of the experimentally‐created gaps. Poor survivorship of weeds within this range, however, suggests that larger gaps are required for regeneration.