Spinifex grasses, Triodia and Plectrachne spp., dominate the vegetation cover at the Argyle Diamond Mine (Kimberley, Western Australia) but are conspicuously absent from rehabilitated areas. The desire of the mining company to return these key ecological species to disturbed areas provided an opportunity to examine the restoration ecology of endemic grasses which dominate vegetation assemblages across a purported 22% of the Australian mainland.

Consuccessional studies of spinifex populations and plants subject to both natural and manufactured disturbances identified fire tolerant (facultative seeder-sprouter), fire resistant (obligate sprouter) and fire sensitive (obligate seeder), clonal and non-clonal species. Recruitment studies distinguished propagule sources which actuated the protocols employed to propagate species for restoration. Combined with fecundity studies, recruitment observations also provided insight into the capacity of natural populations to withstand disturbance facilitating prediction of the period required for regenerating stands to attain reproductive maturity and replenish propagule reserves.

Propagation experiments examined the potential of various sources of propagules identified in recruitment studies to provide plants for restoration activities. Vegetative propagation methods applied to resprouting and/or clonal species provided a simple, reliable and cost-effective method for generating greenstock for restoration which has since been successfully adopted for other spinifex grasses and native Australian grass genera including obligate seeder species.

Examination of topsoil revealed significant levels of soil stored seed reserves in populations of seeder species. These soil seed banks are triggered to germinate by the passage of fire. Further examination of post-fire seedling recruitment suggests that the removal of mature vegetation provides the predominant germination stimulus, which when combined with possible additive effects including the influx of nutrients and smoke residues to the soil following fire result in establishment of seedlings in numbers often equivalent or well in excess of pre-disturbance plant densities. Inhibition of germination of soil stored seed by the presence of mature vegetation suggests allelopathic or plant biomass (living and litter biomass) regulation of recruitment events ensuring restriction to instances where the standing vegetation has been completely removed or extensively depleted. The failure of respread topsoil to realise plant recruitment in rehabilitated areas is an area requiring further research to determine whether alterations to topsoil management practices can improve return from this ostensibly untapped propagule source.

Seeder species were observed to produce a large number of seed (often thousands of units m^-2) providing a substantial source of propagules for restoration. Seed production is tightly regulated by seasonal conditions, predominantly the magnitude and timing of rainfall events. Germination of whole seed in a modified liquid embryo culture media indicated high viability in filled grains (up to 80%) with high seed:ovule ratios (ca. 50%) for Plectrachne spp. from the Argyle site dependent on the season or population sampled. This method was applied successfully to other spinifex species and provides the first reliable and accurate means for establishing the viability of seed through germination in what have previously been deemed germination recalcitrant species.

Germination studies on seed collected from different populations over successive seasons have identified polymorphic dormancy mechanisms which were observed to vary both spatially and temporally. Correspondingly, experiments examining the effect of presowing treatments on germination elicited a varied response with three treatments, aerosol smoking, imbibition in nitrate solutions and long term (18 month) storage eliciting a significant enhancement of germination in some cohorts. Of these treatments long term storage provided the more consistent results indicating a prerequisite for an after-ripening requirement following seed dehiscence.

Analysis of the genetic variation of Plectrachne bynoei, P. pungens, P. schinzii and Triodia intermedia was undertaken using molecular markers. For what appears to be the first time molecular based genetic studies (RAPD) were used to delineate genomic boundaries within spinifex grasslands to identify the extent of the local provenance. Genetic variability within populations and species was also ascertained. This information has been used to design collection protocols for propagule material which ensure maintenance of the variability of the local provenance.

Observations of plant growth and resource allocation identified a pause-pulse response to rainfall events resulting in a typically seasonal pattern although species exhibited a capacity to respond to unseasonal rainfall events. Rainfall events are followed by greening of tussocks as extant shoot components senesce with nutrient reserves remobilised into the new season’s emerging shoots. Tiller initiation, anthesis, fertilisation and seed maturation and dehiscence occur within a six to eight week period following the onset of the first rains. The reconstruction of the photosynthetic apparatus and reproductive effort in the initial weeks of the wet season severely deplete plant resource reserves and is followed by a period of rapid nutrient and dry matter accumulation for the remainder of the wet season and the first months of the dry season while soil moisture remains available to plants.

Studies of seedling growth and nutrient acquisition and allocation under nursery and field conditions identified the ability of species to survive a broad range of environmental conditions. Seedlings exhibited a capacity for high rates of growth and nutrient accumulation under favourable conditions. Seedlings also exhibited a capacity to enter a virtual dormant state facilitating survival under pauperate conditions or periods of intensive competition from neighbouring vegetation.

Revegetation studies realised the potential of both greenstock and broadcast seed application to establish plants in post-mined sites. Successive observations of plant growth, survival and maturation in restored plots were compared with identical data gleaned from natural populations. Observations confirmed that plants established in post-mine areas exhibited similar to higher survival and growth as natural propagules, attaining limited reproductive capacity earlier than seedlings in undisturbed natural stands.