Post-Fire Dynamics of Cool Temperate Rainforest in the O'shannassy Catchment
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Post-fire dynamics of Cool Temperate Rainforest in the O’Shannassy Catchment A. Tolsma, R. Hale, G. Sutter and M. Kohout July 2019 Arthur Rylah Institute for Environmental Research Technical Report Series No. 298 Arthur Rylah Institute for Environmental Research Department of Environment, Land, Water and Planning PO Box 137 Heidelberg, Victoria 3084 Phone (03) 9450 8600 Website: www.ari.vic.gov.au Citation: Tolsma, A., Hale, R., Sutter, G. and Kohout, M. (2019). Post-fire dynamics of Cool Temperate Rainforest in the O’Shannassy Catchment. Arthur Rylah Institute for Environmental Research Technical Report Series No. 298. Department of Environment, Land, Water and Planning, Heidelberg, Victoria. Front cover photo: Small stand of Cool Temperate Rainforest grading to Cool Temperate Mixed Forest with fire-killed Mountain Ash, O’Shannassy Catchment, East Central Highlands (Arn Tolsma). © The State of Victoria Department of Environment, Land, Water and Planning 2019 This work is licensed under a Creative Commons Attribution 3.0 Australia licence. You are free to re-use the work under that licence, on the condition that you credit the State of Victoria as author. The licence does not apply to any images, photographs or branding, including the Victorian Coat of Arms, the Victorian Government logo, the Department of Environment, Land, Water and Planning logo and the Arthur Rylah Institute logo. To view a copy of this licence, visit http://creativecommons.org/licenses/by/3.0/au/deed.en Printed by Melbourne Polytechnic Printroom ISSN 1835-3827 (Print) ISSN 1835-3835 (pdf/online/MS word) ISBN 978-1-76077-589-6 (Print) ISBN 978-1-76077-590-2 (pdf/online/MS word) Disclaimer This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Accessibility If you would like to receive this publication in an alternative format, please telephone the DELWP Customer Service Centre on 136 186, email [email protected] or contact us via the National Relay Service on 133 677 or www.relayservice.com.au. This document is also available on the internet at www.delwp.vic.gov.au Post-fire dynamics of Cool Temperate Rainforest in the O’Shannassy Catchment Arn Tolsma, Rob Hale, Geoff Sutter and Michele Kohout Date Arthur Rylah Institute for Environmental Research Technical Report Series No. 298 Acknowledgements This project was funded by Parks Victoria. Marie Keatley, Dan Nugent, Adam Whitchurch and John Stoner (Parks Victoria) instigated the research and/or provided research direction, information and support. Tim Sanders and Mario Malovic (Melbourne Water) provided logistical information and facilitated access to the O’Shannassy closed catchment area. David Cameron (DELWP) provided invaluable comments on the draft report. Matt White (Arthur Rylah Institute) provided spatial layers for the analysis and sage advice, Ben Fanson and Jim Thomson provided guidance for statistical analyses, and Annette Muir provided comments that improved the final report. All research on public land was conducted under Permit No. 10008220 (issued by Department of Environment, Land, Water and Planning). ii Post-fire dynamics of Cool Temperate Rainforest Contents Acknowledgements ii Summary 4 1 Introduction 5 2 Methods 8 2.1 Study area 8 2.2 Site selection 8 2.3 Field surveys 11 2.4 Analysis of field survey data 12 2.4.1 Vegetation assemblages 12 2.4.2 Species richness and cover 12 2.4.3 Recruitment of Mountain Ash 12 2.5 Spatial analysis 12 3 Results 14 3.1 Field surveys 14 3.1.1 Do vegetation assemblages differ by fire severity class or forest type? 14 3.1.2 Do species richness and cover differ by fire severity class or forest type? 14 3.1.3 How does recruitment of Mountain Ash relate to seed source? 19 3.2 Spatial analysis 19 3.2.1 Changes in rainforest areal extent 19 3.2.2 Probability of rainforest loss as a function of fire severity 22 3.3 Is deer activity of concern? 23 4 Discussion 24 4.1 Changes in vegetation assemblages and structure from field survey data 24 4.1.1 Floristic composition and richness 24 4.1.2 Floristic structure 25 4.2 Eucalypt invasion and rainforest resilience 28 4.3 Deer activity 31 4.4 Pathogens 31 4.5 Conclusion and recommendations 32 References 33 Appendix 1 – Plot summary 37 Appendix 2 – Supplementary Material 39 Summary Context: Cool Temperate Rainforest is an endangered Ecological Vegetation Class generally found in wet, climatically-protected niches where fire has historically been rare. However, since European settlement, there have been substantial changes to land use in surrounding forests and an increase in the frequency of fire. Cool Temperate Rainforest may not be adapted to such perturbations, with implications for post-fire successional processes and long-term recovery and persistence. Aims: This project aimed to determine the dynamics of post-fire regeneration of Cool Temperate Rainforest in the O’Shannassy Catchment (Victorian East Central Highlands), the influence of pre-fire overstorey composition on structural changes, and the extent to which the rainforest community is likely to persist in its ‘natural’ state. Methods: Field surveys were undertaken in 24 plots in and around the O’Shannassy Catchment during March/April 2019. These plots were a mix of Cool Temperate Rainforest and Cool Temperate Mixed Forest (a seral stage of rainforest) and were unburnt or burnt at various intensities by bushfire in 2009. Parameters included overstorey and understorey plant composition, ground cover, and post-2009 tree recruitment. Remotely-sensed data were then used to determine the impacts of fire on the most severely burnt parts of the catchment which could not be safely accessed. Pre- and post-fire data were compared to determine how much rainforest had been lost as a function of fire severity. Results: Ten years post-fire, burnt plots remained compositionally different to unburnt plots, with burnt plots having higher cover of forbs, grasses and shrubs, but substantially lower tree cover. Only ferns appear to have recovered to the unburnt state. The primary rainforest species Myrtle Beech and Southern Sassafras were resprouting from the bases of top-killed parent trees, and eucalypt and wattle species were regenerating strongly from seed. Encroachment of non-rainforest canopy species into rainforest was related to fire severity. Spatial analysis indicated that non-rainforest tree recruitment in the most severely burnt area of the catchment had been sufficiently high that 96% of primary rainforest mapped pre-fire could no longer be classified as such. Encroachment of eucalypts into plots burnt at moderate severity was more limited, and no recruits were noted in plots burnt at low severity or unburnt. This study suggests that some rainforest stands should persist in the O’Shannassy Catchment, but they will mostly be restricted to the most fire- protected parts of the landscape. Despite some documented resistance to fire, rainforest in the O’Shannassy Catchment could not cope with the highest severity fire. Conclusions and implications: Severe fire in 2009 has led to the loss of around two thirds of the Cool Temperate Rainforest previously mapped in the O’Shannassy Catchment. Remaining rainforest stands here and elsewhere in Victoria are further threatened by predicted increases in the frequency and intensity of fire due to climate change, and the long-term future of this important vegetation type appears bleak. While little can be done at a local scale to combat direct impacts of climate change, management should aim to protect or buffer remaining rainforest from indirect impacts and other threats. 1. Remaining rainforest needs to be protected as much as possible from fire. Management options are limited within the catchment itself, hence actions need to be undertaken at a much broader landscape scale, preferably using a cross-tenure approach. 2. Infrastructure activity, especially roadworks, near stands of rainforest should be undertaken in a manner that minimises spread of pathogens such as Myrtle Wilt. 3. Deer monitoring and control should continue in the catchment, as population numbers are expected to increase with time-since-fire. 4 Post-fire dynamics of Cool Temperate Rainforest 1 Introduction Rainforests are the remnants of the oldest extant vegetation in Australia which, in the Cretaceous or early Tertiary, dominated most of the continent (Busby 1992; Kershaw 1992). Following the break-up of the super- continent Gondwana, the opening up of rainforest accelerated as rainfall decreased and became more variable, and after around 2.7 million years ago, with a switch from a summer to winter rainfall regime, rainforest became increasingly restricted to locally favourable, moist areas (Kershaw 1992). Further decreases in rainforest extent within the last glacial-interglacial period appeared to correspond with the arrival of aboriginal people and the development of more fire-promoting vegetation (Kershaw 1992). Previous Bioclim analysis suggested that only around 1% of the Australian continent is now climatically suited to rainforest (Busby 1992), and this proportion may already be decreasing. Cool Temperate Rainforest is an Ecological Vegetation Class (EVC) listed under Victoria’s Flora and Fauna Guarantee Act 1988 (FFG) (DELWP 2018). In its most mature state (without emergent eucalypts) it is characterised by a more-or-less continuous rainforest tree canopy of variable height, mostly forming narrow linear strips along the margins of streams (DSE 2009). In the Central Highlands, the overstorey is dominated by Myrtle Beech (Nothofagus cunninghamii), the mid-storey includes Southern Sassafras (Atherosperma moschatum) and Blackwood (Acacia melanoxylon), and the understorey is dominated by tree ferns and ground ferns (Cameron and Turner 1996; DSE 2009).