Soil seed banks of secondary vegetation on the Port Hills and Banks Peninsula, Canterbury, New Zealand, and their role in succession

Abstract

Soil seed banks at 21 sites covered with poor quality pasture, bracken femland, scrubland of broom or gorse, and various forest types, were examined by germinating seed in soil samples. At most sites the composition of upper and lower soil layers was similar. Persistent, deeply buried seed banks of Cytisus scoparius, Ulex europaeus, and more rarely Sophora microphylla, were discovered at seven sites, four of which lacked that particular species in the above-ground vegetation, and are thus considered to be of a former vegetation type. Forest sites tended to have more seeds and more species represented in the soil seed bank. Although an average of only 35% of the species in the seed bank were represented above ground at the sampling point, this rose to 60% within 5 m, and 72% within 10 m of that point. Those species further away were mostly widespread pasture weeds, even within forest sites, and are interpreted as being recently dispersed and transient. Large quantities of Juncus spp. in some sites are believed to be transported by water movement through the soil. Some species, including certain site dominants, were poorly or never represented in the soil seed bank. It is considered that the seed bank has an important role in establishing the initial floristic composition following disturbance. However, differential seedling survival, resprouting, and competition probably help in maintaining the pre-disturbance vegetation at non-forest sites. Where forest is disturbed, especially by burning, there is the potential for a completely different vegetation to develop from the seed bank.

Keywords:

• soil seed banks
• persistent buried seed
• transient seed
• Cytisus scoparius
• Ulex europaeus
• pasture
• scrub
• bracken
• secondary forest
• succession
• initial floristics