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.
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.
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.
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.