Natural re-seeding and Trifolium repens demography in grazed hill pastures. II. Seedling appearance and survival.
The appearance and survival of Trifolium repens seedlings from naturally deposited seed were monitored for 3 years under different sheep grazing managements and P fertilizer treatments in 4 slope/aspect zones in New Zealand hill country. A mean of 6 seedlings/m2 per year appeared, representing 4.2% of the seeds deposited each summer. Only 4.4% of seedlings survived to form established, stolon-bearing plants, representing a mean recruitment rate of one seedling/5.5 m2 per year. Survival was highest on steep NW sites (10%), and nil on flat SW sites, reflecting likely competitive stresses from surrounding vegetation. Such low recruitment rates clearly indicate seedling regeneration plays only a minor role in T. repens persistence in this environment. Vegetative stolon densities of 3000-4000/m2 and high rates of stolon initiation and death confirm that the species behaves essentially as a true perennial. A useful ecological role for low seedling recruitment rates in maintaining genetic diversity within the T. repens population must be recognized, however, especially in highly variable environments.