Moira Grass seed bank study (Barmah Forest). Final Report.
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The presence of extensive plains of Moira Grass (Pseudoraphis spinescens (R.Br.) Vickery) contributes to the ecological character of Barmah Forest, and presence of the species forms part of the criteria that were required for Barmah Forest to be listed under the Ramsar Convention. One of the environmental watering objectives for Barmah Forest is to ‘promote healthy and diverse vegetation communities, with an emphasis on restoring natural range and distribution of Giant Rush, Moira Grass, River Red Gum forest and River Red Gum woodland in at least 55% of the Barmah–Millewa icon site’. However, the knowledge base for managing flows within Barmah Forest for optimal growth of Moira Grass is limited. Current watering regimes require the flooding of Moira Grass wetlands in winter/spring to a minimum depth of 50 cm to promote the growth of Moira Grass and prevent the encroachment of River Red Gum and Giant Rush. From 1997 until 2009, south-eastern Australia was subjected to severe drought. In 2010–12, substantial flooding occurred that inundated most of Barmah Forest, but the response of the aquatic plant communities was poor, leading to speculation that the preceding 10 years of drought had had a negative impact on the viability of the dormant seed bank and/or the viability of Moira Grass propagules. This project was designed to investigate whether Moira Grass seeds were present in the seed bank of six wetlands in Barmah Forest after an environmental watering event in spring 2013. Preliminary field surveys indicated that Moira Grass was still present in three of these wetlands, however was no longer present in the remaining three wetlands (K. Ward pers com). Sediment was collected from all six wetlands and the presence and viability of the Moira Grass seed bank assessed by: • a 12-week germination trial • separation of seeds from the sediment to allow the direct counting of seeds • viability testing of the seeds separated from the sediment • DNA analysis of the sediment to indicate the potential pool of Moira Grass present. Seeds were collected opportunistically from mature plants in the southern Murray–Darling Basin. As Barmah Forest is at the southernmost limit of Moira Grass distribution, sediment was also obtained from a wetland in Kakadu National Park in the Northern Territory, to allow comparisons to be made of the number of Moira Grass seeds and their viability. Very few monocotyledon seedlings germinated from the wetlands in which Moira Grass is now absent compared with wetlands in which Moira Grass is still present, and none of these were identified as Moira Grass. However, direct counting indicated that seeds with the Moira Grass morphology were still present in all wetlands, although assessed as less than 2% viable for wetlands at which Moira Grass is still present and non-viable in wetlands where it is absent. In comparison, the proportion of viable seeds collected from mature plants ranged from 16 to 27%. When seeds were separated from sediment from Kakadu National Park, 5 to 27% were found to be viable. Technical constraints meant we were not able to trial a DNA detection method directly on sediment samples. DNA methods for grasses are in their infancy, but we were able to develop an assay to amplify a useful DNA barcode from known specimens. While we made good progress, significant work is still required to develop a method, where the presence of plants at a site can be determined by simply examining and detecting their DNA in a soil sample. We now consider the validation of a reference sequence/barcode for Moira Grass as a project within itself, which would include examining other unpublished database barcodes, thus potentially expanding the range of choice. These results indicate that the seed bank of Moira Grass within the sediment of Barmah Forest is limited, with no indication of a long-term viable seed bank and that recruitment of this plant is likely coming from below-ground stolons and/or existing rootstock.