The relationship between seed rain and the soil seed bank in a temperate rainforest stand near Auckland, New Zealand

Abstract

Composition of the germinable seed rain and the soil seed bank is documented for five sites in temperate rainforest near Auckland, New Zealand, in an effort to understand the dynamics of the soil seed bank. The seed rain added a mean of 202 ± 93 germinable seeds per 0.1 m2 over 15 months to the forest floor in 1988 and a total of 40 species (range 15–25 per site). The source of seeds included both native forest species growing on-site, and adventive species of which most were growing off-site. Species richness of the seed rain was highest in summer (32 species) and lowest in winter (6 species). However, density of the recorded seed rain was highest in late autumn-early winter from high seed rain and massive germination in May and June of seeds from the native tree, Kunzea ericoides, at two sites in the early stages of forest regrowth. Seed germination from soil samples which had been denied seed inputs for 15 mo identified the density (52 ± 41/0.1m2) and composition (18 species, range 2–9) of the ‘persistent’ component of the seed bank (i.e., seed longevity >1 y). Native woody species were poorly represented in the persistent seed bank relative to native herbs and adventives. An estimated 10% of the annual seed rain enters the persistent soil seed bank. The presence, and dynamics of turnover for most species in the persistent seed bank can be explained as a balance between additions of new individuals and loss of old individuals over one to a few years. At the same time, the combination of high persistent seed bank densities and low seed rain inputs for a few adventive species (e.g., Phytolacca octandra, Juncus bufonius) indicates that seed of these species may derive from individuals which grew at or near the site at some time in the past. © 1996 Taylor & Francis Group, LLC.