Aspects of the dynamics of the seed-banks and seedling populations of Acacia victoriae and Cassia spp. in arid western New South Wales

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Abstract

Acacia victoriae, Cassia nemophila and C. phyllodinea are shrubs which occur throughout large areas of arid and semi-arid Australia. This paper examines aspects of the dynamics of the seed-banks and seedling populations of these plants to determine their influence upon recruitment frequency. Seed-banks in the soil are large, ranging from 50 to 3900 seeds m-2for A. victoriae and from 5 to 400 seeds m-2for Cassia spp. A large proportion (ca. 80%) of these seeds are viable. Seedling densities soon after emergence range up to 25.7 m-2for A. victoriae and up to 21.7 m-2for Cassia spp. Any individual cohort of seedlings represents only a small proportion (< 6%) of the total seed-bank. Most viable seeds fail to germinate even when adequate moisture is available. Seedling mortality rates are high (ca. 100%) during the first 12 months after germination. If recruitment of these shrubs is intermittent, it is most likely a result of low seedling survival rather than infrequent germination.

Ancillary