THE SIZE AND COMPOSITION OF SOIL SEED-BANKS IN REMNANT PATCHES OF 3 STRUCTURAL RAIN-FOREST TYPES IN NORTH-QUEENSLAND

The size and species composition of the soil seed‐bank in a remnant patch of each of three structurally and floristically distinct rainforests (Complex Mesophyll Vine Forest, Complex Notophyll Vine Forest and Semi‐Evergreen Vine Thicket) were assessed. Seeds of 94 species germinated from 12 surface soil samples collected from each site. All three seed‐banks were composed mostly of herbs characteristic of roadsides and agricultural land, and pioneer rainforest trees and shrubs. Agglomerative classifications indicated that the seed‐bank samples from each rainforest remnant had a characteristic species composition and could be distinguished reliably from seed‐bank samples drawn from other sites. Seeds of species present in the standing forest were poorly represented in the seed‐banks except for one long‐lived pioneer tree, Dendrocnide photinophylla, at one site. The seed‐bank from the seasonally dry vine thicket was significantly larger (4000 seeds m‐2) than those from the two moister sites (400–600 seeds m‐2, contained more seeds of roadside and agricultural herbs, and fewer seeds of rainforest pioneer and secondary shrubs and trees. We suggest three explanations for the different seed‐bank structure observed in the seasonally dry forest site. First, with increased deciduousness in rainforests, seed‐banks are increasingly subject to invasion and domination by seeds of rapidly maturing herbs. Second, long‐lived seeds that germinate in canopy gaps would be less likely to accumulate under deciduous forests because they would he exposed annually to conditions suitable for germination. Third, chronic disturbance by cattle and pigs produces sites suitable for the establishment of rapidly maturing herbs, and possibly disperses their seeds into the forest. Copyright © 1990, Wiley Blackwell. All rights reserved