Ecosystem Restoration

Restoration of Australia's native plant communities and the landscapes they occupy is a land management imperative. Retention of native perennial cover is crucial for biodiversity conservation and the continued provision of the biological and physical services that it provides for our agricultural production systems. Effective landscape management is a multi-step process involving: (i) identification of a target landscape's role (e.g. conservation, recreation, production); (ii) quantification of the current extent and condition of remnant vegetation; (iii) rehabilitation to improve the quality and long-term viability of existing remnants, and large-scale revegetation to increase regional cover.

An ever-expanding effort is going into remnant rehabilitation as well as on ground revegetation. However, quantitative research on how to maximise the success of critical revegetation and rehabilitation projects is generally lacking. In particular, two areas of research that hold great promise for achieving these goals in a cost-effective and timely fashion are: (i) genetic issues to do with seed quality provenance, and; (ii) re-establishing the symbiotic plant-soil microbe relationships on which many key ecological processes are based.


Genetic Provenance Guidelines for Sourcing Native Plant Seed

With regard to sourcing seed for revegetation or restoration two genetic issues are of primary importance: (i) fitness (how vigorous the genotype is), with the main problem being avoidance of inbred seed that give poor germination and growth due to low heterozygosity and; (ii) provenance (ensuring that the seed chosen to be sown in a particular area are adapted to local environments). Current seed sourcing practices acknowledge these potential problems by recommending a 'precautionary approach' to collection – sourcing seed only from large populations (probably outbred) within a few kilometres of the target sites (probably locally adapted) for replanting.

Although intuitively appealing, such guidelines are based on very little information about the geographic scale of genetic differentiation within the Australian flora. For many species that probably have relatively little local adaptation the precautionary approach is likely to be unnecessarily restrictive, imposing expensive logistical constraints on seed sourcing activities that have no biological value. For those that do show significant small-scale genetic variation of ecological importance, and which may very well be obligate inbreeders, locally sourced seed, even if from mildly inbred populations, may be more appropriate than seed from large populations that are further away from the planting area. Clearly the potential for tradeoffs between inbreeding and provenance are very real.

Variation in growth and morphology in Swainsona recta

This problem is illustrated by the case of Swainsona recta, a grassland herb targeted for restoration in southeastern Australia. For this species, seed collected from small populations have low germination and poor growth relative to those from large populations due to high levels of inbreeding. In the southern part of the range, only small populations remain, so it has been proposed to collect vigorous outbred seed from large northern populations. However, common garden growth studies show significant morphological differentiation between northern and southern populations that is probably of ecological significance. Evidence of similar effects exist for Acacia acinacea, an important revegetation species being used extensively by Greening Australia in the Murray-Darling Basin.

The purpose of this research project is to combine high-resolution genetic markers and growth studies (provenance trials) to identify characteristics of remnant populations that will make them sources of high genetic quality seed, and to determine over what geographical scales adaptively significant genetic differentiation occurs. This information will then be used to: (i) provide quantitatively based genetic provenance maps for key species that can be used to guide seed collection activities and; (ii) develop general collecting guidelines for different ecological classes of species that will maximise the likelihood of collecting high genetic quality seed that is locally adapted.

By addressing issues of genetic fitness and provenance simultaneously for a range of key native species commonly used in revegetation, it will be possible to develop a general set of guidelines providing information about what characteristics make a population a likely source of outbred 'fit' seed, and how far can that seed be moved around the landscape and still remain locally adapted. Using such information as a basis for seed sourcing practice will lead to real improvements in revegetation success.


Using Microbial Symbionts to Improve Revegetation & Rehabilitation of Australian Landscapes

A second major knowledge gap is information on symbiotic interactions between plants and soil organisms (mycorrhizal fungi, nitrogen-fixing actinomycetes and rhizobia). These relationships promote rapid early growth and increased survival extending beyond host plants to other species in the community, and are likely to significantly impact on remnant structure and viability. In fact, many plant species important in early phases of re-establishment are themselves dependent on these symbioses. However, these micro-organisms rapidly vanish from agricultural soils, particularly where native shrubs have been cleared through cropping or where continual grazing has occurred over long periods. As a result, beneficial symbionts may be absent from disturbed soils where revegetation is most crucial.

On-going research is exploring how plant-microbe interactions can be used to improve the effectiveness of revegetation programs, and to determine when it will be necessary to inoculate soils with appropriate symbionts. We are in the initial stages of a large-scale collaborative field trial with Greening Australia Victoria and the North Central Catchment Authority in Victoria that will provide an opportunity to assess the value of using native shrubby legumes and rhizobia in revegetation efforts (with a particular focus on areas where dryland salinity is a major issue). The project involves 6-10 Acacia species for which we are currently isolating appropriate rhizobial strains, as well as a range of Eucalyptus spp. and other non-legumes. The trial is being carried out across 3 geographically distinct areas within the catchment covering a range of soil and moisture regimes. Replicated sites using inoculated and uninoculated Acacia seed are being set up within each area, and a range of information on the abundance of native rhizobia, germination, growth and survival (of both legume and non-legume species) collected over an 18-24 month period.

Scientific Staff: Broadhurst, Burdon, Thrall, Young, West