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Native grasses for revegetation
Revegetation of billabong banks with Wheat grass and Weeping grass
Revegetation has been defined as the introduction of additional vegetation into a degraded area. Commonly this involves introducing perennial plants that are somewhat similar to those that might have previously been present. Using this definition there are many ways in which revegetation can be achieved from “indigenous trees and shrubs”, to “non-indigenous trees and shrubs”, to Blue Gums, to farm forestry, to native grasses (Rural Solutions SA, 2001).
At Native Seeds, our interest lies in revegetation with native grasses and we ask that people consider using native grasses as well as trees and shrubs. Grasses are the primary colonisers of new landscapes. They hold the fresh and unstable soil together and in doing so they establish the soil conditions for the successful establishment of the secondary and tertiary colonisers – the shrubs and trees.
There is a distinction between conservation and revegetation. Revegetation is actively reintroducing material onto a site that either no longer occurs there naturally or is in such low occurrence that it cannot yield sufficient seed to permit natural recruitment of following generations. Conservation, on the other hand, is more about retaining what is on site and undertaking steps to increase its occurrence. Native Seeds provides seed for revegetation.
The aim of any revegetation project will influence the choice of species and the methods used. The following paragraphs outline some possible underlying principles of revegetation projects.
Revegetation for low maintenance
Many native grasses have relatively constant biomass production without the large peaks of production often found with exotic grasses. This growth form, which usually provides fresh green leaves throughout most of the year, lends itself to low maintenance through reduced mowing requirements.
Similarly most native grasses, once successfully established, will persist for many years and will continue to provide a satisfactory ground cover for decades after sowing. This means that the on-going maintenance need for resowing is reduced, if not eliminated.
The most common use for low maintenance is in revegetation of roadsides or minesites where the main aim is to provide a persistent ground cover that requires relatively little mowing, requires no overseeding and does not provide a fire hazard once established.
Revegetation for biodiversity
The intention of many revegetation programs is to restore a degraded site with the full array of plants that would have been present originally. In complex vegetation communities this can mean as many as 20 to 30 species of plants. While this is desirable, for many relatively short term revegetation programs of 2 to 3 years, it is simply insufficient time to restore complex ecosystems. Native Seeds believes it is better to establish one strong backbone species on a site and then slowly increase the biodiversity by adding seed or plants of other species at a slow pace, possibly over a decade or more. The choice of a grass for a backbone species is sensible as they are easy to sow and establish, have many known characters including herbicide tolerances for many weeds and are widely suited to this use.
Once a strong backbone species of grass is sown and established, it can then be maintained for a year or so to reduce the weed-seed burden within the topsoil and thereby reduce the chance of major weed explosions when the site is later disturbed. After a year, it is then possible to progressively introduce other species without having to hand weed.
A revegetated native grassland area once fully functional can be a reasonably close replica of the original ecosystem and can support a broad array of native insects, animals and microflora. These can then in turn provide many of the essential fungi for the establishment of other native plant species which require them for successful establishment.
Revegetation for perenniality
Australia has shallow and poor soils with an underlying salt burden and a variable climate. This environment requires more perennial plants. Many experts trace the increasing problem of dryland salinity to the reduction of perennial plants within the Australian landscape. This reduction has permitted recharge of the water table and the development of salinity further downstream.
The use of native grasses that are adapted to a site will lead to greater numbers of perennial plants, greater interception of groundwater recharge and ultimately reduce dryland salinity.
Naturally native grasses are not the only plants that can achieve this aim and can only be considered as one part of the solution, but they can provide a valuable perennial component on sites where other plants are not able to grow and persist. |
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