When revegetation projects are undertaken, there is occasionally a demand for seed of local provenance, that is seed which has been gathered from the local area where revegetation is to occur. This is because the local trees and shrubs have adapted well to that environment and local material of these plants usually does perform better. Many people assume that the same rule will apply to grasses.
While local provenance is relevant for trees and shrubs, it is not relevant for revegetation using native grasses because of the way grasses reproduce. It is often assumed that cross pollination is the normal fertilisation for all plants, but this is not so for native grasses. While there is considerable variety in the way Australian native grasses flower and produce seed, all the grasses studied to date produce the majority of their seed by some form of self-pollination and not by cross pollination. Many grasses including Wallaby grass and Weeping grass are self fertilising and spikelets are fertilised before they emerge from the leaf sheath. Some grasses are able to produce fertile seed asexually. The grasses don’t display inbreeding characteristics because they have more than two basic sets of chromosomes. Kangaroo grass, for example, has from two to six sets of chromosomes and Weeping grass has four sets of chromosomes. Other grasses such as Redgrass and Bluegrass species have some flower spikelets with two sets of chromosomes, while others on the same plant may have many sets of chromosomes.
Thus there is genetic diversity within each plant rather than within different individuals within a population. So there can be distinct genetic variations within one species in the same paddock. It then becomes impossible to determine what is local.
Furthermore, distance is not a factor in determining genetic diversity for native grasses. Studies have shown that different types of Wallaby grass, Rytidosperma caespitosum, can be found with different characteristics within one to two kilometres. We know that in other areas variation is far less and the same type can extend to several hundred kilometres. Both wild species and bred cultivars of native grasses will grow well outside their normal range thus displaying broad scale adaptation.
Often too, there is a fear that by introducing new genotypes of species into an area that the local population of plants will be contaminated. As the native grasses are self fertilising, out-crossing is likely to be very infrequent with a minimal risk of contamination of other plants.
Long term studies over many years of native grasslands, have shown there are quite rapid changes in the dominant species in the grassland community. Thus the grasslands themselves are constantly changing in response to climate and other environmental factors. The introduction of native grass seeds from commercially available sources should improve genetic diversity and there should be no concerns about unwanted contamination of species through outcrossing as the grasses are self fertilising.