Year

2014

Degree Name

BEnviSc Hons

Department

School of Earth & Environmental Science

Advisor(s)

Ben Gooden

Abstract

Soil seed banks act as reservoirs of diversity for plant communities and can be vital to the re-establishment of habitats post disturbance. Whilst terrestrial seed banks have been well studied, relatively little is known about seed banks of estuarine plant communities across the coastal landscape. Despite this, coastal ecosystems are among the most threatened in the world and a detailed understanding of seed bank dynamics could play a critical role in their restoration. The aim of this study was to quantify the composition of seed banks, and determine how they are related to the composition of above ground vegetation, in three threatened estuarine plant communities, swamp-oak forest, saltmarsh and mangrove forest, at three locations on the south coast of New South Wales, Australia. More specifically, variation in seed banks was examined at three spatial scales: (1) amongst the three vegetation communities; (2) between single species-dominated microsites within the saltmarsh community; and (3) with soil depth. The seedling emergence method was used to determine the identity and quantity of seeds in the seed bank by collecting soil cores of known volume, placing them in greenhouses under conditions favourable to germination, and counting and identifying individual seedlings as they emerged. In total, 9117 seedlings emerged from 87 species and seed banks varied significantly with community type in density, richness and composition. Saltmarsh communities had the largest density of seeds and swamp-oak forests were the most species-rich. Although the seed banks were much richer in species, the abundance of the dominant species in the seed bank largely reflected the species assemblage of these above ground plant communities. In contrast, mangrove forests had relatively low densities of seeds, which were predominantly from plants typical of the saltmarsh. Across all vegetation communities, the seed bank was dominated by a few saltmarsh species, and Juncus kraussii and Samolus repens collectively accounted for 75% of germinating seedlings. Within saltmarsh, fine scale variation in the densities of seeds was related to variation in dominant above ground vegetation for some species. Seeds were present at all depths, but seed density and species richness varied with soil depth, with the greatest number of species occurring in the upper most layers of soil. This first study of seed banks across the coastal estuarine landscape in Australia revealed that in general seed banks among communities are distinct and represent the key taxa of the above ground communities, despite the presence of additional species. Considering their critically threatened status in New South Wales, the rich and abundant seed bank present in swamp-oak and saltmarsh communities is likely to play an integral role to their population dynamics, natural resilience and restoration.

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