Date of Award

2020

Degree Name

Doctor of Philosophy (College of Arts and Science)

Schools and Centres

Arts & Sciences

First Supervisor

Associate Professor Dylan Korczynskyj

Second Supervisor

Andrew Grigg

Third Supervisor

Professor Max Bulsara

Abstract

Seedling densities at establishment of jarrah (Eucalyptus marginata D. Don ex Sm.) and marri (Corymbia calophylla (Lindl). K. D. Hill & L. A. S. Johnson) following bauxite mining in the Northern Jarrah Forest of south-western Australia are variable and few factors explored during 40 years of field studies have explained this variability. This study explored establishment within the framework of limitation due to amount of seed supply and number of suitable microsites for establishment. First, relationships were identified between seedling establishment densities on 654 mine sites restored between 1998 and 2017 and restoration practices (seed and fertiliser application rates), climate conditions (rainfall evenness and seasonal air temperatures) and seed supply (measured as proportion of forest perimeter). Then, canopy-stored seed as a seed source on restoration sites, and its influence on seedling densities, was investigated. Mean (± SE) jarrah seedfall in the first 12.7 m of the forest edges was 10,000 ± 2,624 seeds/ha/year. The variable, but potentially high, jarrah seedfall within 12.7 m of forest edge is an important seed source influencing jarrah seedling densities on restoration sites, but there was very low presence of marri seed in both forest and restoration sites. Last, three complementary field trials were implemented to investigate the importance of microsite characteristics on jarrah and marri seedling establishment in the restoration system. Seedling survival to establishment was high, 83.9–89.2% for jarrah and 93.8–96.8% marri, and survival was not related to microtopography generated by soil ripping or substrate type. However, seedling density was highest in furrows for both species, most likely because of seed movement during surface water run-off. Also, marri density at establishment increased with sulphur and organic carbon and decreased with soil conductivity. Net seed supply of jarrah and marri over a restoration site (including both canopy-stored and sown seed) is variable, and supply, rather than microsite characteristics, is the most likely limitation to seedling establishment.

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