Controlling the soil seedbank of the invasive grass Andropogon gayanus (gamba) for mine site restoration in the Australian tropical savanna

Student thesis: Other thesis - CDU

Abstract

Tropical savannas are a globally important ecosystem, supporting a high level of biodiversity and endemism, as well as a range of ecosystem services and land uses. Invasive grasses pose a major threat to savannas, with disturbed areas such as mine sites particularly vulnerable to invasion. Andropogon gayanus is a highly invasive grass which is threatening threatening to invade vast areas of the northern Australian savanna. Andropogon gayanus spreads easily and creates monospecific stands of tall invasive grass. The high fuel loads of A. gayanus increase fire frequency and intensity and have substantial impacts on native plant communities and savanna ecosystems. As a result, A. gayanus poses land management challenges to mine site restoration. At Rum Jungle mine in the Northern Territory, A. gayanus has reached extreme levels of plant density, comprising nearly 50% of all weed infestations. Seed spread is the major vector for colonisation and perpetuation of A. gayanus population, yet current management strategies do not focus on the A. gayanus soil seedbank.

This project aimed to identify management treatments that effectively control the soil seedbank of A. gayanus, while allowing the establishment of woody plants for revegetation purposes. Chemical, physical and biological treatments were applied in the field in the late dry season 2016 and emergence and survival of A. gayanus seedlings monitored over a two-month period in early 2017. Residual herbicides were most effective in reducing seedling emergence with average emergence of 1.1 ± 0.4 seedlings m-2 compared to 2.7 ± 1.4 seedlings m-2 in the untreated control. The treatments did not affect growth and survival of woody plant seedlings.

The results of this study have a range of management implications. Andropogon gayanus recruitment takes place during the wet season, when access to remote locations such as mine sites may be limited. The ability to apply soil seedbank treatments in the late dry season that will effectively prevent A. gayanus emergence during the wet season provides a powerful management tool for land managers. This may be used as part of an integrated weed management approach, targeting the A. gayanus soil seedbank alongside above ground mature A. gayanus plants.

Management treatments covering a range of costs were trialled. The most effective treatment (sulfometuron) had a purchase price similar to glyphosate, which is the currently preferred treatment for A. gayanus. Subject to future research, the herbicides found to significantly reduce seedling emergence in A. gayanus may also help manage the risk of glyphosate resistance in A. gayanus. Several weed species have developed resistance to glyphosate under single-herbicide management regimes; we have identified a choice of herbicides potentially suitable for managing the risk.

Date of Award2017
Original languageEnglish
SupervisorNatalie Rossiter - Rachor (Supervisor), Sean Bellairs (Supervisor) & Garry Cook (Supervisor)

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