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Flora Monitoring on the Revegetation Trial to Inform Rehabilitation Design for the Former Rum Jungle Mine Site Prepared for: Department of Mines and Energy Prepared by: EcOz Environmental Consultants 2 016 1. www.ecoz.com.au This page has been intentionally left blank Client: Department of Mines and Energy ii Doc Title: Rum Jungle Rehabilitation Trial – Monitoring 2016 Document Control Record Document Code: EZ15131-C0301-EST-R-0001 Catalogue Number: 63397 Project Manager: Chris Brady Author(s): Chris Brady and Nicole Clark Approved by: Jeff Richardson Approval date: 25 May 2016 DOCUMENT HISTORY Version Issue Date Brief Description Reviewer/Approver 1.A - B 29 Mar 2016 Report preparation by authors Authors 1.C 30 Mar 2016 Internal review Jeff Richardson 1.D 31 Mar 2016 Draft sent to client Jeff Richardson 2.A 24 May 2016 Response to DME comments Jeff Richardson 3.A 25 May 2016 Final version sent to client Jeff Richardson Recipients are responsible for eliminating all superseded documents in their possession. EcOz Pty Ltd. ABN: 81 143 989 039 Telephone: +61 8 8981 1100 Winlow House, 3rd Floor Facsimile: +61 8 8981 1102 75 Woods Street Email: [email protected] DARWIN NT 0800 Internet: www.ecoz.com.au GPO Box 381, Darwin NT 0800 Cover page: Photograph of an area of with vigorous Acacia and Eucalypt growth near sample plot RV11. RELIANCE, USES and LIMITATIONS This report is copyright and is to be used only for its intended purpose by the intended recipient, and is not to be copied or used in any other way. The report may be relied upon for its intended purpose within the limits of the following disclaimer. This study, report and analyses have been based on the information available to EcOz Environmental Consultants at the time of preparation. EcOz Environmental Consultants accepts responsibility for the report and its conclusions to the extent that the information was sufficient and accurate at the time of preparation. EcOz Environmental Consultants does not take responsibility for errors and omissions due to incorrect information or information not available to EcOz Environmental Consultants at the time of preparation of the study, report or analyses. Client: Department of Mines and Energy iii Doc Title: Rum Jungle Rehabilitation Trial – Monitoring 2016 This page has been intentionally left blank Client: Department of Mines and Energy iv Doc Title: Rum Jungle Rehabilitation Trial – Monitoring 2016 Executive Summary This report summarises the findings of monitoring of the Borrow Area 5 rehabilitation trial at the Rum Jungle former mine site. It is noted that reconstructed landscape proposed for Rum Jungle will have a variety of landscapes and that the findings here will not be applicable to all areas. The aim of the revegetation trial is to grow a woodland of local native species. The method trialled was weed control and direct seeding. Also, in an attempt to limit Gamba Grass invasion an area was seeded with Silk Sorghum. This monitoring event occurred 14 months after the area was seeded. The rehabilitation is therefore at an early stage of growth somewhat limiting conclusions that can be drawn at this early stage. A diversity of tree and shrubs species seedlings are present and there was a dense ground cover, dominated by native grasses in most areas. The density of stems is within the range of a Top-End woodland. Acacias were the most common woody plant species with Acacia oncinocarpa the most common. Eucalypts were present, with Eucalyptus miniata the most common. Although only recently seeded these results indicate that the area could be on a trajectory towards a woodland community dominated by local species. Two other possible trajectories are proposed: a vegetation community dominated by Gamba Grass or a vegetation community dominated by Acacia. Monitoring on an annual or every second year basis until short lived Acacias die out will provide valuable information on likely trajectory for later rehabilitation work. There was considerable variation in Gamba Grass cover between sites. Of the two Silk Sorghum sites one site had the second highest Gamba Grass cover, the other the second lowest. Thus conclusions on the effectiveness of the Silk Sorghum trial cannot be made except to note that other variables may be affecting results and further replication is required to test this. From these results Silk Sorghum did not eliminate Gamba Grass (although it may hinder its growth). Management of Gamba Grass will be an important component of rehabilitation efforts at Rum Jungle as without management of Gamba Grass and fire the area may be a Gamba Grass dominated grassland. Recommendations from this trial include: • Add more Eucalypt seeds to the seed mix for further seeding particularly Eucalyptus tetrodonta, and Ironwood. This should include Corymbia polysciada and Corymbia grandifolia as they have self-seeded and are growing in the surrounding area. • Carry out seed viability trials before any future seeding and use the results to adjust the seed mix. • Consider tailoring the seed mix to site specific conditions (e.g. adding additional Melaleuca seed to areas likely to be seasonally inundated). • Investigate and if possible correct the low seed viability of many of the species in the seed mix. In the event it cannot be improved: o Consider the use of top soil and/or inoculation with mycorrhizal fungi to increase the density and diversity of Eucalypts in rehabilitation areas. o Consider the use of tubestock to increase density and diversity. • Investigate and address the low number of some important mid storey species such as Buchanania obovata and Terminalia ferdinandiana and include some of the self-seeded mid storey species into the seed mix. • Continue Gamba Grass and Mission Grass control on a regular basis as these grassy weeds have the potential to promote hot fires that will kill desirable canopy species. • Investigate the mechanism of Gamba Grass spread at the site to facilitate management. • Investigate the range of options for managing Gamba Grass, this may include establishing a Gamba Grass buffer around the perimeter (e.g. a cleared or heavily grazed area). Monitoring of the revegetation should continue as it will provide valuable information to inform the rehabilitation methods. Important questions include the effects of competition between woody species and grasses, will Acacia dominance persist and will the lack of Eucalypt diversity effect the resilience of the Client: Department of Mines and Energy v Doc Title: Rum Jungle Rehabilitation Trial – Monitoring 2016 community? To facilitate this monitoring all woody plants in the 11 vegetation plots have been tagged and information collected about their immediate surrounds. Adding plots in areas with vigorous growth and relatively bare areas may provide useful information for factors influencing wood plant growth. To determine specific completion criteria requires a stratification of the proposed reconstructed landform and consideration of factors that will limit revegetation in these areas. Using this information realistic goals should be set based on surrounding vegetation communities and knowledge from other mine sites. More targeted studies of surrounding communities and other rehabilitation areas may be required to inform revegetation of these specific communities. Goals should be set in conjunction with consultation with Traditional Owners. Completion criteria should remain, at this stage, broad and generic as specific completion criteria may set unrealistic expectations and erroneously be used to develop rehabilitation procedures (such as seed mix) and will limit what is considered successful rehabilitation. This conclusion is reinforced by the variability between sites: it may be that a single completion criteria may be incorrect and different edaphic (and other) profiles may be found to lead to other vegetation communities reflecting the diversity of environments and complex conditions likely at the site. A summary of the response to the project scope is given in the cross reference table below. Client: Department of Mines and Energy vi Doc Title: Rum Jungle Rehabilitation Trial – Monitoring 2016 Task from scope Key points Section Indicators of revegetation/ecosystem success A high level summary of the role of indicators is provided. 6.1 The rehabilitation strategy aims to be consistent with the views and interests of Traditional Owners. The setting of indicators of revegetation success must therefore reflect their aspirations and expectations. A stated objective of Traditional Owners is restoring flora and fauna species endemic to the site and its immediate surrounds (NTG 2013). This is very broad, further discussion may yield key culturally significant species. There will be a diversity of environments created during rehabilitation and the vegetation communities they can support will be variable. Indicators will be specific for each environment. Before any specific indicators are chosen the range of environments needs to be identified along with the limitations for re-vegetation considered (soil properties, slopes, water movement etc.). The role of silk sorghum as a cover crop Silk Sorghum has not prevented the establishment of Gamba Grass, but may hinder its 5.4 growth. Woody plants species and densities in the Silk Sorghum trial area were within the range of other sites. Monitoring until Silk Sorghum dies out is required to determine if the Silk Sorghum cover crop influences growth rates and make-up of rehabilitation communities. Further replication may provide more conclusive results. Proposed monitoring program including detailed The monitoring program that was undertaken for this report was submitted to DME (Mitchell Memo information on methodology, timing, team etc. Rider) of 1 February 2016. A suggested monitoring program for ongoing monitoring is provided in Appendix A. Appendix A Compare species sown with what species are Given the presence of numerous woody plants the revegetation method and timing of works 4 present, considering germination testing results; can be considered appropriate to allow woody plants to establish.