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BushfireConf2017 - 28. More burning, more warts: Frequent burning favours cane toads

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This presentation by Diana Virkki of Griffith University discusses how differing fire regimes (i.e. repeated fires, variable fire histories and wildfire) influence native ground-dwelling anuran communities and cane toad abundance in sclerophyll forests of southeast Queensland.

Presentation from Nature Conservation Council of NSW 2017 Bushfire Conference - Fire, Fauna & Ferals: from backyards to bush

Published in: Environment
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BushfireConf2017 - 28. More burning, more warts: Frequent burning favours cane toads

  1. 1. More burning, more warts: Frequent burning favours cane toads Diana Virkki (Griffith University) Cuong Tran (Ten Rivers) Tom Lewis (DAF) Guy Castley (Griffith University)
  2. 2.  Disturbance processes and invasive species  Synergistic effects on native species (Anson et al. 2013; McGregor et al. 2014; McGregor et al. 2015) Open landscapes Habitat generalists Invasive species Improve dispersal Increase access to prey Introduction (McGregor et al. 2014)
  3. 3.  Frequent burning – commonplace as land management tool Fire Reduces vegetation cover and homogenises landscape Habitat structure Favour invasive species Fire as a landscape disturbance process
  4. 4.  Rhinella marina  Impacts on native fauna  Native to S America  Introduced to NQ in 1935  Fire  commonly used  Relationships with fire, native anurans and cane toads unknown  Ecologically appropriate and sustainable fire management regimes ? Cane toads
  5. 5. Native anurans and cane toads  Anurans  Habitat heterogeneity (Mac Nally et al. 2001, Williams and Hero 2001, Price et al. 2010)  Structural features, i.e. leaf litter, CWD  Habitat features reduced by fire  E.g. Burrowing frog (Myobatrachus gouldii) and wood frogs (Rana sylvatica) require thick litter affected by fuel reduction burning (Bamford 1992; Rittenhouse and Semlitsch 2007)  Cane toads  Open habitats (Zug and Zug 1979, Brown et al. 2006)  Influence of disturbance, adding to pressure of invasive cane toads
  6. 6.  SEQ – impacted by cane toads  Do differing fire regimes (i.e. repeated fires, variable fire histories and wildfire) influence native ground-dwelling anuran communities and cane toad abundances in dry sclerophyll forests of southeast Queensland?  Hypothesis: Aims Burning Habitat Heterogeneity = + Native anurans + Cane toads
  7. 7. Study sites  Subtropical climate mar approx. 1000 mm St Mary Tiaro Bauple Queensland Study region Australia Dry sclerophyll forest 60 Km Fire history  Variable  Long-term fire experiment
  8. 8. Legend " ³ Study plots Fire Treatment Bauple Treatments AB LU TB WF Comparative Treatments SM01 SMWF T01 T03 Bruce Highway Forest boundary 0 4 82 Kilometers
  9. 9.  Four surveys at 35 plots  2 × winter, 2 × spring-summer (2010 – 2013)  4 trap nights  Predictor variables:  Habitat structure  Structural features  Heterogeneity  Fire - spatial  Rainfall (BOM) Data Collection
  10. 10.  Changes in vegetation communities along transects  Shannon-Wiener diversity index; H = ∑(ni/N) ln(ni/N) Habitat Heterogeneity  ni = species richness or length per patch  N = total species or number of patches
  11. 11. Results summary Dependent variable Treatment favoured Treatment × season Native abundance TB Richness AB, TB, WF Cane toad - Rhinella marina* AB Striped marsh frog – Limnodynastes peronii* TB, LU Northern banjo frog – L. terraereginae* No preference Spotted marsh frog - L. tasmaniensis* No preference Spring Total significant (P<0.05) 3 1 Great barred frog - Mixophyes fasciolatus LU Tusked frog - Adelotus brevis LU Ornate Burrowing frog - Platyplectrum ornatum TB Copper-backed brood frog - Pseudophryne raveni TB Green-thighed frog - Litoria brevipalmata AB Smooth toadlet - Uperoleia laevigata Mixed Longer unburned 10 year - unburned Annually burned Wildfire Key Triennially burned
  12. 12.  Figure. Anuran variables with a significant (P<0.05) treatment effect, showing mean ± S.E. a) native anuran abundance, b) anuran richness and c) Limnodynastes peronii abundance. Effects of fire treatment on anurans AB TB WF SMWF SM01 T03 T01 LU 0 2 4 6 8 10 12 Nativeanuranabundance a ab ab bc bc bc c c AB TB WF SMWF SM01 T03 T01 LU Treatment 0 1 2 3 4 5 6 Anuranrichness a a a b b b b b Treatment AB TB WF SMWF SM01 T03 T01 LU Treatment 0 1 2 3 4 5 6 Limnodynastesperonii a a b b b b a) b) c) Nativeanuran abundance Anuranrichness Stripedmarsh frogabundance
  13. 13.  Figure. Anuran variables with significant (P<0.05) interactive effects of treatment × season, with seasons separate, showing mean ± S.E. a) total anuran abundance and b) Rhinella marina abundance. Spring Winter AB TB WF SMWF SM01 T03 T01 LU Treatment 0 10 20 30 40 50 60 70 Totalanuranabundance a b bcbc c cc c AB TB WF SMWF SM01 T03 T01 LU Treatment 0 2 4 6 8 10 12 Totalanuranabundance AB TB WF SMWF SM01 T03 T01 LU Treatment 0 1 2 3 4 Rhinellamarina AB TB WF SMWF SM01 T03 T01 LU Treatment 0 10 20 30 40 50 60 Rhinellamarina a b bc bc bc bc bc c Effects of fire treatment × seasonality on anurans Spring Winter a) b) Totalanuran abundance Canetoad abundance
  14. 14.  Figure. Scatter plot of Limnodynastes terraereginae abundance with time since fire (back transformed ln scale), showing line of best fit (linear) and r2 for significantly correlated (P<0.05) abundances. Effects of time since fire 0 0.7 1.7 3.5 6.4 11 19 32 53.5 89 Time since fire (ln scale) 0 2 4 6 8 10 12Limnodynastesterraereginae r2 = 0.115 - Northern banjo frog Limnodynastes terraereginae Northernbanjofrog abundance
  15. 15. Figure. Scatter plots of significant (P<0.05) anuran relationships with number of fires (back transformed ln scale), showing line of best fit (linear or quadratic) and r2 for a) anuran abundance, b) anuran richness, c) Rhinella marina abundance and d) Limnodynastes tasmaniensis abundance. 0 0.7 1.7 3.5 6.4 11 19 32 0 1 2 3 4 5 6 7 8 9 Anuranrichness r2 = 0.066 b) 0 0.7 1.7 3.5 6.4 11 19 32 Fire frequency (ln scale) 0 20 40 60 80 100 Rhinellamarina r2 = 0.254 c) Number of fires (ln scale) 0 0.7 1.7 3.5 6.4 11 19 32 Fire frequency (ln scale) 0 2 4 6 8 10 Limnodynastestasmaniensis r2 = 0.094 d) Number of fires (ln scale) 0 0.7 1.7 3.5 6.4 11 19 32 0 20 40 60 80 100 120 Totalanuranabundance r2 = 0.248 a) Effects of number of fires + a) Total anuran abundance b) Richness c) Cane Toad Rhinella marina d) Spotted Marsh Frog Limnodynastes tasmaniensis Totalanuran abundance Anuranrichness Canetoad abundance Spottedmarsh frogabundance
  16. 16.  * represents species modelled using AICc when over dispersion was minimal.  Table 5. Model-averaged coefficients ± confidence intervals of explanatory habitat, fire and weather variables from negative binomial Generalised Linear Mixed Models on anuran abundance, richness and species-specific abundances. Bold values indicate where coefficient confidence intervals do not overlap zero. Determining the most important variables for anurans Dependent variable Predictor variables Bare CWD Number of fires Canopy H’ Ground H’ Litter Rainfall R2 glmm(m) Total abundance 0.07 ± 0.38 -0.27 ± 0.29 -0.16 ± 0.37 -0.09 ± 0.26 0.25 ± 0.28 0.09 ± 0.33 0.20 ± 0.34 0.02 Native abundance 0.13 ± 0.43 -0.01 ± 0.34 Number of fires 0.52 ± 0.37 0.06 ± 0.28 Ground H’ 0.66 ± 0.38 0.16 ± 0.32 0.25 ± 0.38 0.08 Richness 0.16 ± 0.17 -0.08 ± 0.17 0.15 ± 0.19 0.07 ± 0.17 0.14 ± 0.18 -0.03 ± 0.19 Rainfall 0.18 ± 0.17 0.07 Limnodynastes peronii 0.13 ± 0.56 -0.03 ± 0.38 0.35 ± 0.48 -0.06 ± 0.30 Ground H’ 0.67 ± 0.43 0.23 ± 0.42 0.39 ± 0.41 0.03 L. tasmaniensis* 0.42 ± 0.93 -0.82 ± 1.19 0.58 ± 1.15 0.76 ± 1.05 0.24 ± 1.04 -0.96 ± 1.01 0.10 ± 0.97 0.01 L. terraereginae* 0.02 ± 0.52 0.30 ± 0.52 Number of fires 0.70 ± 0.47 Canopy H’ 0.55 ± 0.49 Ground H’ 0.81 ± 0.49 0.43 ± 0.44 0.12 ± 0.49 0.52 Rhinella marina 0.34 ± 0.52 -0.16 ± 0.37 0.16 ± 0.60 -0.09 ± 0.33 0.06 ± 0.39 Litter -0.47 ± 0.36 Rainfall 0.52 ± 0.38 0.08 Total Significant 2 1 3 1 2
  17. 17. Distance from watercourse R² = 0.0155 0 5 10 15 20 25 0 200 400 600 800 1000 1200 R² = 4E-05 0 1 2 3 4 5 6 7 8 9 0 200 400 600 800 1000 1200 R² = 0.0182 0 10 20 30 40 50 60 70 80 90 100 0 200 400 600 800 1000 1200 Anuranrichness Canetoad abundance Nativeanuran abundance Figure. Scatter plots anuran relationships with distance to nearest creekline (moderate to major stream based on q-spatial data), showing line of best fit (linear) and r2 for a) native anuran abundance, b) anuran richness, and c) Rhinella marina abundance. Distance to nearest creekline (m) (Moderate – Major stream, Q-spatial data) Distance to nearest creekline (m) (Moderate – Major stream, Q-spatial data) a) b) c)
  18. 18. Discussion  Anurans persisted with frequent fire events  Refuted hypothesis: frequent burning reduces habitat H’ and negatively impacts on anurans  Long-term fire experiment, favoured anurans  Regular (small-scale) low intensity fires  Fine-scale patchiness playing a role  Scale of patchiness  Fine-scale patchiness or large unburnt patches? Annually burnt plot – Bauple State Forest
  19. 19.  Anurans often unaffected or positively affected by fire (Hannah et al. 1998, Keyser et al. 2004, Perry et al. 2009, Lowe et al. 2013)  Avoid mortality  Moist microhabitat  Retreat underground or into water (Perry et al. 2009, Lowe et al. 2013)  Congruent with results  low intensity burns  Particularly for cane toads Anurans and fire
  20. 20. Toad preferences  Favoured very frequently burned sites  Annually burned and triennially burned sites  Past research (USA)  Cane toads  negatively associated with litter preferred frequently disturbed areas  More abundant in open grassland and disturbed habitats Species Trends with fire References Cane toad Not described Dwarf American toad Bufo americanus charlessmithi More abundant 1 yr post-fire Perry et al. 2009 American toad B. americanus Higher numbers in burnt forest Kirkland et al. 1996, Greenberg and Waldrop 2008 Boreal toad Anaxyrus boreas Abundance tripled in the 3yrs after fire Hossack et al. 2013
  21. 21. Habitat Heterogeneity  Anuran richness related to habitat heterogeneity (Dupuis et al. 1995, Delis et al. 1996, Pearman 1997, Williams and Hero 2001).  Canopy and ground H’  key predictors  Important for native species  Repeated burning may reduce fine-scale habitat H’  Patchy, mosaic burns important  Guidelines for DSF in SEQ: 40-80% mosaic  Ideal scale of patchiness unknown
  22. 22. Summary  Species not excluded from frequent burns  Positive outcomes:  Anurans resilient to fires  Negative outcomes:  Cane toads favoured at frequently burnt areas  Potential impacts on natives through:  Competition or predation (Boland 2004, Greenlees et al. 2006)  Ingestion of toxins (Phillips et al. 2003) Land managers need to consider this in fire management if planning for biodiversity outcomes Important in high risk areas, i.e. vulnerable wetlands or areas with threatened anurans
  23. 23. Dr Diana Virkki – virkkid@tenrivers.com.au Dr Cuong Tran Dr Tom Lewis Dr Guy Castley

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