Riparian seed banks: a potential tool for revegetation to support riparian management and restoration

This thesis research focuses on soil and sediment seed banks within riparian zones and their potential application for the regeneration of riparian vegetation to support river management or river restoration activities. The research was carried out in the lower Hunter Valley catchment in south eastern Australia, and addresses four main aims: 1) to detect spatial trends in seed bank species richness, abundance and composition within the riparian zone and 2) to identify drivers of seed bank variability; 3) to assess the potential contribution of the seed bank to riparian vegetation and geomorphic river recovery; and 4) present implications for the use of seed bank-based revegetation as a tool in river management and restoration. The research examines the traits of species detected in the seed bank in relation to geomorphology and sedimentology, and perhaps most innovatively, biogeomorphology – the study of reciprocal interactions between vegetation and geomorphology that drive the succession of both. Four studies investigate: 1) riparian seed bank stratification in relation to geomorphology; 2) relationships between seed bank spatial variability, geomorphology and sedimentology; 3) the potential role of riparian seed banks in supporting biogeomorphic succession and river recovery; and 4) seed bank composition in relation to riparian condition. Collectively the research findings contribute a framework for distinguishing between areas of potentially high and low seed bank species richness (and to some extent abundance) in any riparian system, based on simple field indicators including vegetation, sedimentology and geomorphology. The research emphasises the suitability of riparian seed banks to support the stabilisation of sediment through the regeneration of the pioneer species which were found to dominate the seed bank. Potential challenges for seed bank-based revegetation are raised, such as the increasing presence of exotic and terrestrial species with riparian degradation. The thesis highlights situations for which seed-bank based regeneration may be particularly useful,such as initiating channel contraction processes through sediment stabilisation and aiding the establishment of groundcover in highly degraded river reaches.