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Recalcitrant Species
What are recalcitrant plant species?
Many of the dominant jarrah forest understorey plant species are “obligate resprouters†and over thousands or millions of years of evolution have abandoned seed as a method of reproduction. These ancient species grow and spread by sending out vegetative shoots and underground rhizomes and bulbs. These vegetative adaptations are ideally suited to recovering from fires, grazing and drought, which are regular occurrences in the natural jarrah forest. They do not produce viable seed, or if they do it is difficult to collect, or does not readily germinate. As a result, some of these species are under-represented in rehabilitated areas compared with the forest vegetation because they do not readily establish from the natural seed in the topsoil that is returned or from applied seed.
These difficult plants are known as recalcitrant species, and they often play an important role in the jarrah forest ecosystem. For example, common dry land sedges are a favourite food source for kangaroos in the rehabilitated areas. They also resprout quickly and vigorously after disturbances such as fire, and hence give the forest resilience to such disturbances.
Propagation of recalcitrant species
Alcoa's commitment to restore the plant species of the jarrah forest after mining meant that planting, not seeding, of these recalcitrant species was required. Not only did they have to be physically planted these species, but methods to propagate them needed to be developed for the large quantities of plants needed for rehabilitation.
Despite being common in the jarrah forest, these species have not been previously grown in the horticultural industry and so little was known about them. The easiest method to grow plants is from seed, but with some species this requires treatments to overcome dormancy of the seeds. If this is not possible then tissue culture or cuttings are used.
Tissue culture is the most difficult and expensive propagation method and is only used when other methods fail. The development of successful tissue culture methods is a very slow and expensive process, and it can take several years to work out how to mass produce some species. A tissue culture laboratory at the Marrinup Nursery was first established in 1996, and then enlarged to produce recalcitrant plants for all of Alcoa’s mine rehabilitation areas.
Planting recalcitrant plant species in mine rehabilitation
All rehabilitated mine pits are now planted with recalcitrant species. Since production-scale planting began in 1998, the number of recalcitrant plants established in the rehabilitated areas has increased to approximately 200,000 each year. The plants are grown from seed, cuttings or tissue culture at the Marrinup nursery.
Grazing protection for recalcitrant species
Recalcitrant plants are expensive to produce. Many of the recalcitrant species planted in Alcoa’s mine rehabilitation are a favourite food source of kangaroos. These kangaroos often eat all of the above ground biomass of the plant, or pull the plant out of the ground. To protect these recalcitrant species, those species known to be a favoured food source are planted in a nylon mesh (or onion) bag. These mesh bags allow the plants to naturally grow and spread through and out of the bag, whilst providing protection for enough of the plant to allow it to survive.
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